SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 601 IN-DEPTH REVIEW Light and Laser-based Treatments for Hidradenitis Suppurativa: A Systematic Review Ilya M. Mukovozov BHSc, MSc, MD, PhD1*, Sara Mirali BSc, PhD2*, Sophie Khaslavsky BScN3, Sunil Kalia MD, MHSc, FAAD, FRCPC1,4,5 * Equal contribution 1 Department of Dermatology and Skin Science, University of British Columbia, Vancouver, BC, Canada 2 Faculty of Medicine, University of Toronto, Toronto, ON, Canada 3 Vancouver General Hospital, Vancouver, BC, Canada 4 Photomedicine Institute and Centre for Clinical Epidemiology & Evaluation, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada 5 British Columbia Children’s Hospital Research Institute, Vancouver, BC, Canada Hidradenitis suppurativa (HS) is characterized by painful, recurrent papules and nodules occurring mainly in intertriginous areas. The pain, odor, and disfigurement caused by HS significantly impacts patients’ quality of life and is associated with increased rates of anxiety and depression.1-3 Moreover, the symptoms of HS can be physically limiting and interfere with employment and personal functioning.4, 5 Early diagnosis and management of HS reduces the risk of disease progression.6 Treatment for HS are often multimodal and include medical, surgical, and laser and light-based therapies. Although treatment with tumor necrosis factor inhibitors, interleukin-1 inhibitors, antibiotics and others have been reported, these ABSTRACT Background: Hidradenitis suppurativa (HS) is characterized by painful, recurrent lesions occurring mainly in intertriginous areas. The pain, odor, and disfigurement caused by HS significantly impacts quality of life and is challenging to treat. A comprehensive systematic review evaluating the use of light and laser-based treatments for HS is lacking. Methods: We performed a systematic review by searching Cochrane, MEDLINE and Embase. Title, abstract and full text screening, and data abstraction were done in duplicate. Results: Forty studies met the inclusion criteria, representing a total of 821 patients. Included studies were comprised of 5 randomized within-patient controlled trials, 1 randomized controlled trial, and 34 case series. Overall, treatments with the most reported cases were laser surgery, photodynamic therapy (PDT), and laser field treatments which showed a response in 80% (n=344/431), 73% (n=122/167) and 71% (n=84/101) of treated patients respectively. The pooled response rate for psoralen plus ultraviolet A was 69% (n=9/13). Conclusion: Our results suggest that laser surgery using carbon dioxide (CO2) laser or a combination of CO2 and Nd:YAG lasers has a moderate response rate for HS with the most reported cases. Laser for field treatment and PDT also had moderate response rates with a large number of reported cases. However, extrapolation of these results may be limited due to the majority of the studies being case series, lack of standardized outcomes being assessed, and insufficient long term follow up results. INTRODUCTION SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 602 treatments may be associated with significant cost, adverse effects, declining efficacy, and possible drug-drug interactions. In practice, patients may express the preference to avoid systemic treatments if possible. Light and laser-based management is known to be a safe and effective treatment option for many dermatological conditions. Furthermore, light and laser-based treatment provides the advantage of avoiding the adverse effects and drug interactions associated with systemic therapies. Light and laser-based treatments commonly employed for HS include psoralen plus ultraviolet A (PUVA), photodynamic therapy (PDT), neodymium- doped yttrium aluminum garnet (Nd:YAG) laser, carbon dioxide (CO2) laser, and others7-10. These treatments are thought to reduce HS lesions by debulking tissue and by reducing the amount of hair follicles, sebaceous glands, and bacterial load.11 Although laser and light-based treatments for HS have been reported, little is known about their comparative effectiveness. The aim of this systematic review is to summarize outcomes for light and laser-based treatments used for HS, enabling physicians to better predict clinical response. A systematic review of the literature was conducted adhering to PRISMA reporting guidelines.12 The study protocol was registered in the PROSPERO database (CRD42020223612). Study eligibility criteria Eligibility criteria for this review were: • Population: individuals of any age and sex with HS • Intervention (exposure): Nd:YAG laser, PDT, CO2 laser, intense pulse light (IPL), PUVA • Comparator: patients with HS not exposed to intervention • Outcomes: pain, lesion count, hidradenitis severity score (HSS), visual analogue scale (VAS), dermatology life quality index (DLQI), recurrence, healing time, physician global assessment (PGA), sartorius score, lesion area and severity index (LASI), patient satisfaction, clinical response • Study design: cohort, cross-sectional, and case-series Literature search and screening MEDLINE, Embase, the Cochrane Database of Systematic Reviews, and PubMed were searched on June 12, 2020 using variations of the keywords “hidradenitis suppurativa” and “light” (Tables S1-S4). No date or language restrictions were applied. Title, abstract, and full-text screening were conducted by two independent reviewers (I.M., S.M.) using Covidence online systematic review software (www.covidence.org). Any conflicts between reviewers were resolved by discussion until a consensus was reached. Data extraction Data extraction was completed by three independent reviewers (I.M., S.M., S.K.) on a standardized extraction form. Level of evidence assessment Level of evidence was assessed using a modified hierarchy proposed by Guyatt and Sackett, where: (1) prospective controlled trial; (2) retrospective study or large case series; (3) small case series.13 Data synthesis METHODS http://www.covidence.org/ SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 603 After data collection, we determined that quantitative evidence synthesis was not feasible due to differences between the studies included in our review. Specifically, differences in study design, HS severity, heterogeneity in treatment modalities, patient populations, and outcome measurement. Instead, our results are presented in narrative form for each outcome Study selection Our literature search yielded 460 articles, 405 of which were excluded based on title and abstract review (Figure 1). Of the 55 studies retrieved for full text screening, 15 were excluded. A total of 40 studies were ultimately included in the review, 6 of which were conference abstracts. The included studies were published between 1987 and 2020 and included 5 randomized within-patient controlled trials, 1 randomized controlled trial, and 34 case series (Table 1). The majority of studies were conducted in Spain (n=7), North America (n=6), United Kingdom (n=5), and Italy (n=4) (Table 1). Patient characteristics (age/sex) In total, our pooled analysis includes 821 patients, 87% (n=623/716) females, with mean age of 33 years, ranging from 15 to 73 years of age. Targeted phototherapy A total of 22 studies14-35 included in our review reported on targeted phototherapy using lasers and energy-based devices in patients with HS, representing a sample size of 724 patients with a mean age of 37.2 years (range: 14-73), and 76.3% (n=497/651†) were female. Overall, targeted phototherapy improved lesions in 77.6% (n=413/532) of HS patients. Adverse effects were reported in 22.9% (n=122/532) of treated patients (Table 2). CO2 CO2 laser was employed in 10 studies (n=396), with 78.5% (n=311/396) of patients showing improvement (Table 2).15-17, 19-21, 24- 26, 28 Adverse events were reported in 26.2% of cases (n=103/393). All 10 studies found that CO2 laser was an effective treatment modality. In a study of 24 patients, Lapins et al. showed that CO2 laser treatment with healing by secondary intention was safe, beneficial, and rapidly effective with a mean resolution period of 4 weeks. The majority of patients (91.7%, n=22/24) experienced no recurrence in treated areas. Overall, all patients reported satisfaction with this treatment modality.24 The treatments were well tolerated in all patients, and average healing time post procedure was 8.8 weeks.21 Among patients with recurrent HS, Mikkelsen et al. found that CO2 laser surgery with healing by secondary intention was effective with high patient satisfaction rates (94.8%, n=55/58). Improvement was reported as great in 75.8% (n=44/58) of patients and mild in 19.0% (n=11/58). Overall, 91.4% (n=53/58) of patients stated they would recommend the procedure.28 Nd:YAG Four studies consisting of 92 patients reported on the use of Nd:YAG in HS27, 29, 32, 33. Among studies with reported outcomes, 85% (n=30/35) of treated patients showed improvement (Table 2) and adverse events were reported in 15% of cases (n=8/53). Overall, 3 of the 4 studies found that Nd:YAG laser RESULTS SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 604 Figure 1: PRISMA diagram of study selection process treatment improved HS.27, 32, 33 In a study of 15 HS patients, Vossen et al. found that Nd:YAG for hair removal prevented disease progression. Patients reported a decrease in the number of monthly flares and average HS disease severity, as measured by a numerical response scale (NRS), was significantly lower post treatment (NRS 6.4 ± 2.8 vs NRS 3.6 ± 3.5). Overall, 67% (n=10/15) of patients recommended the treatment.32 Nd:YAG/CO2 combined Two studies combined Nd:YAG and CO2 laser treatment (n=58), with both reporting a benefit in HS (Table 3).14, 23 In a study comparing Nd:YAG laser with combined CO2 and Nd:YAG lasers in 20 patients, combination treatment resulted in better outcomes compared to Nd:YAG alone (mean improvement in CO2 and Nd:YAG: 90% ± 20.52 vs mean improvement in Nd:YAG: 70.68% ± 23.55). Other lasers Two studies (n=31) reported on the use of ‘other’ lasers, including PEHT (Pediatric Endoscopic Hidradenitis Treatment) and diode laser in HS patients.18, 34 Collectively, treatment showed improvement in 93.5% (n=29/31) of patients studied. In a study by Esposito et al., PEHT was found to be an effective treatment for HS and patients reported satisfaction with results. Recurrence in untreated locations was reported in only 18% (n=2/11) of patients, which were successfully resolved using the same treatment.34 In a study by Fabbrocini et al., diode laser reduced Sartorius score, improved HiSCR, and reduced DLQI. Overall, 90% of patients experienced improvement, with 5% (n=1/20) having complete response, 35% (n=7/20) good response, 50% (n=10/20) partial response, OVID EMBASE 419 citations Pubmed 177 citations OVID Medline 169 citations EBM Reviews - Cochrane Database of Systematic Reviews 29 citations 794 studies imported for screening 334 duplicates removed 460 studies screened 405 studies irrelevant 55 studies assessed for eligibility 15 studies excluded: o 6 duplicates o 2 no outcomes (histology only) o 3 case reports o 4 commentaries 40 studies included Id e n ti fi ca ti o n S cr e e n in g E li g ib il it y In cl u d e d SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 605 and 10% (n=2/20) no response. The Sartorius score improved from 28.6 ± 13.0 at baseline to 19.8 ± 12.3 post-treatment.18 IPL Four studies (n=83) in our review assessed the use of IPL for the treatment of HS. Overall, IPL led to improvement in 65% (n=54/83) of patients and adverse events were reported in 25% (n=16/64) (Table 2).22, 30, 31, 35 Highton et al., reported that IPL treatment resulted in long-term clinical improvement of lesions in 17 HS patients in an intra-individual controlled trial. Clinical improvement was also corroborated by independent analysis of clinical photographs and patient reported satisfaction.22 Another study of 25 HS patients found that IPL was useful as an adjuvant treatment for HS patients with mild to moderate disease, and 52% (n=13/25) of patients reported reduced disease activity.31 Photodynamic therapy (PDT) 17 studies8, 36-51 reported on the use of PDT in patients with HS (n=167). The mean age was 33.3 years (range: 17-62) and 68.9% (n=115/167) were female. Overall, PDT was effective in 70.7% (n=118/167) of patients. Adverse events were screened for in 38.3% (n=64/167) of the PDT cohort, and were reported in 35.9% (n=23/64). A number of photosensitizers were used in PDT. Ten studies (n=121)8, 37, 43-46, 48-51 reported on PDT for HS with the photosensitizer aminolevulinic acid (ALA). In this cohort, 78.5% (n=95/121) of treated patients responded. Suarez-Valladares et al. found that in a series of HS patients treated with intralesional ALA-PDT, 76.3% (n=29/38) achieved complete remission.8 In a smaller study of five Hurley stage II or III HS patients with recalcitrant disease, no significant improvement was seen, despite mild improvements in Sartorius score, VAS, and DLQI in all patients (mean change from baseline to post-treatment: Sartorius = -1.6, VAS = -0.3, DLQI = -6.4%). Swelling and blistering was present in 40% (n=2/5) of patients after the first treatment for 8-10 days.52 Other photosensitizers utilized for PDT in HS include methylene blue, methyl amino levulinate, and tetracycline. Overall, four studies consisting of 28 patients were included in this cohort.36, 38, 41, 42 Of those that reported individual patient outcomes, 94.4% (n=17/18) of patients reported improvement. Adverse effects were screened in 72.2% (n=13/18) of patients and of these, adverse effects were reported in 92.3% (n=12/13). Agut-Busquet et al. followed 7 HS Hurley stage II and III patients treated with PDT and methylene blue. PDT and methylene blue treatment improved DLQI and reduced lesion size in 85.7% (n=6/7) of patients after 1 month.36 Relapse was reported in 28.6% (n=2/7) at 7 and 12 weeks post-treatment. Psoralen plus ultraviolet A (PUVA) PUVA to treat HS was examined in a single retrospective chart review.7 A total of 13 patients were treated with a regimen involving a 15 min bath containing 30 mL of 1-2% 8-methoxypsoralen lotion followed by broadband ultraviolet A. Treatments were performed twice weekly, with a median of 25 (range: 3–57) treatments. Overall, five patients were reported to have ‘clear or near clear’ HS, four patients reached ‘moderate clearance’, and four showed ‘no to minimal’ improvement. Overall, bath PUVA was effective in 69% (n=9/13) of patients in this series and was well tolerated. Adverse events were recorded for two patients and included erythema and claustrophobia. SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 606 The studies included in our review reported on patients with both moderate and advanced disease. Many of the studies included in our review utilize laser-based treatments for surgery of affected sites in patients with advanced disease resistant to other therapies. Our results suggest that laser-based surgery is associated with a moderate response rate based on a large sample of pooled patients. Furthermore, many of the studies employing laser devices for surgery of HS lesions included patients with long standing and recalcitrant disease, suggesting that these treatment modalities can be employed an adjuncts with success even in patients with advanced disease. Likewise, treatment modalities that utilize laser-based field therapy of affected areas using Nd:YAG, IPL, or diode laser were associated with a mild response rate based on a large sample of pooled patients. Laser field treatments for HS were employed in patients with both early and advanced disease, suggesting that this treatment modality is appropriate both to treat advanced disease and as a prophylactic therapy to target follicular inflammation and prevent disease progression. A number of adverse events were reported in the studies included in our review. Overall, PDT was associated with the highest rates of reported adverse events (36%). Laser field treatments had less reported adverse events compared to lasers employed for surgical treatment of HS lesions (18% vs 25%). A number of factors may contribute to this observed difference, including differences in study quality and reporting of adverse events, given that only 105 out of 424 patients treated with laser surgery for HS had adverse events recorded. Some of the adverse events reported for laser surgery included pain, infection, hypertrophic scaring, contracture and wound dehiscence. Side effects associated with PDT included pain, erythema, blistering, burning. Bath PUVA was generally well tolerated, although two patients reported erythema and claustrophobia. Collectively, these findings suggest that while light therapy is a moderately effective treatment modality, adverse events are not uncommon, and patients should be counselled on the risks and benefits of light therapy. While the mechanism underlying the effectiveness of light-based treatments for HS are not well understood, several possibilities have been suggested. CO2 laser vaporization and excision removes epithelial sinus tracts which may contain debris and bacteria that can lead to relapse.53 Non- ablative lasers cause thermal damage to the dermis, which may initiate a wound-healing response with upregulation of procollagen mRNA, matrix metalloproteinases, and cytokines that contribute to wound healing.54 Our study has several limitations. Many studies did not report on the side effects of light-based therapies, which restricts our analysis on treatment tolerability. Secondly, some studies reported aggregate data and outcomes for individual patients could not be extracted. Moreover, different outcome measures were used in the studies included in our review, further challenging comparisons between studies. Finally, the majority of the included studies were case series, which limits the generalizability of our analysis. Despite these limitations, our review provides important information that must be DISCUSSION CONCLUSION SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 607 interpreted in a clinical context. First, light- based treatments show moderate benefit in both early and advanced disease. Second, laser devices and PDT have moderate clearance rates for patients with HS, however access to the technology and impractical treatment delivery (especially with extensive disease) may be a barrier. Third, adverse events are not uncommon with light therapy and patients should be counselled on these risks. Though randomized control trials would be the ideal way to validate our findings, studies with treatment comparators are needed to further delineate the therapeutic ladder for HS. Conflict of Interest Disclosures: None Funding: None Corresponding Author: Ilya M. Mukovozov, MD, PhD Skin Care Centre 835 W 10th Ave, Vancouver, BC V5Z 4E8 Phone: (604) 875-5151 Email: ilya.mukovozov@alumni.ubc.ca References: 1. Esmann S, Jemec GB. Psychosocial impact of hidradenitis suppurativa: a qualitative study. Acta Derm Venereol. May 2011;91(3):328-32. doi:10.2340/00015555-1082 2. Matusiak L, Szczech J, Bieniek A, Nowicka- Suszko D, Szepietowski JC. Increased interleukin (IL)-17 serum levels in patients with hidradenitis suppurativa: Implications for treatment with anti- IL-17 agents. Journal of the American Academy of Dermatology. Apr 2017;76(4):670-675. doi:10.1016/j.jaad.2016.10.042 3. Wright S, Strunk A, Garg A. New Onset Depression among Children, Adolescents, and Adults with Hidradenitis Suppurativa. J Am Acad Dermatol. May 2020;doi:10.1016/j.jaad.2020.05.090 4. Alavi A, Anooshirvani N, Kim WB, Coutts P, Sibbald RG. 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Actas Dermo-Sifiliograficas. Jul-Aug 2014;105(6):614-617. doi:10.1016/j.ad.2013.10.016 38. Belotto RA, Tardivo JP, Baptista MS, Santos RE. CLINICAL RESPONSE OF HIDRADENITIS SUPPURATIVA TO PHOTODYNAMIC THERAPY USING TETRACYCLINE AND RL50 (R) LIGHT SOURCE. Lasers in Surgery and Medicine. Mar 2013;45:62-63. 39. Bu WB, Xu XL, Wang Y, et al. Surgery combined with photodynamic therapy for the treatment of Hidradenitis Suppurativa: A report of 7 cases. Photodiagnosis and Photodynamic Therapy. Jun 2017;18:46-49. doi:10.1016/j.pdpdt.2017.01.176 40. Calzavara-Pinton PG, Rossi MT, Aronson E, Sala R, Italian Grp Photodynamic T. A retrospective analysis of real-life practice of off-label photodynamic therapy using methyl aminolevulinate (MAL-PDT) in 20 Italian dermatology departments. Part 1: Inflammatory and aesthetic indications. Photochemical & Photobiological Sciences. 2013;12(1):148-157. doi:10.1039/c2pp25124h 41. Fadel MA, Tawfik AA. New topical photodynamic therapy for treatment of hidradenitis suppurativa using methylene blue niosomal gel: a single- blind, randomized, comparative study. Clinical and Experimental Dermatology. Mar 2015;40(2):116-122. doi:10.1111/ced.12459 42. Abstracts of the 8th European Hidradenitis Suppurativa Foundation (EHSF) Conference, 6-8 February 2019, Wrocław, Poland. Exp Dermatol. Feb 2019;28 Suppl 2:5-55. doi:10.1111/exd.13893 43. Passeron T, Khemis A, Ortonne JP. Pulsed dye laser-mediated photodynamic therapy for acne inversa is not successful: A pilot study on four cases. Journal of Dermatological Treatment. 2009;20(5):297-298. Pii 910443295. doi:10.1080/09546630902882063 44. Rodriguez-Prieto MA, Valladares-Narganes LM, Gonzalez-Sixto B, Noguerol-Cal M. Efficacy of intralesional photodynamic therapy for the treatment of hidradenitis suppurativa. Journal of the American Academy of Dermatology. May 2013;68(5):873-875. doi:10.1016/j.jaad.2012.11.030 45. Sotiriou E, Apalla Z, Maliamani F, Ioannides D. Treatment of recalcitrant hidradenitis suppurativa with photodynamic therapy: report of five cases. Clin Exp Dermatol. Oct 2009;34(7):e235-6. doi:10.1111/j.1365-2230.2008.03094.x 46. Strauss RM, Pollock B, Stables GI, Goulden V, Cunliffe WJ. Photodynamic therapy using aminolaevulinic acid does not lead to clinical improvement in hidradenitis suppurativa. British Journal of Dermatology. Apr 2005;152(4):803- 804. doi:10.1111/j.1365-2133.2005.06475.x 47. Suarez-Valladares M, Espasandin-Arias M, Varas-Meis E, Fernandez-Canga P, Castineiras- Gonzalez J, Rodriguez-Prieto M. Effectiveness of intralesional photodynamic therapy in the management of Hidradenitis Suppurativa. Experimental Dermatology. May 2018;27:31-32. 48. Valladares-Narganes LM, Rodriguez-Prieto MA, Blanco-Suarez MD, Rodriguez-Lage C, Garcia- Doval I. Treatment of hidradenitis suppurativa with intralesional photodynamic therapy using a laser diode attached to an optical cable: a promising new approach. British Journal of Dermatology. Apr 2015;172(4):1136-1139. doi:10.1111/bjd.13385 49. Vilarrasa E, Bittencourt F, Martorell A, Puig L. Photodynamic therapy in the treatment of moderate-to-severe hidradenitis suppurativa: a report of 28 patients. Experimental Dermatology. Feb 2019;28:49-49. http://dx.doi.org/10.1080/09546634.2019.1677842 http://dx.doi.org/10.1080/09546634.2019.1677842 SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 610 50. Zhang LL, Wang PR, Shi L, et al. Topical 5- aminolevulinic acid photodynamic therapy improved refractory acne conglobata and perifolliculitis capitis abscedens et suffodiens rather than hidradenitis suppurativa. Journal of Innovative Optical Health Sciences. Jan 2016;9(1)1640002. doi:10.1142/s1793545816400022 51. Gold M, Bridges TM, Bradshaw VL, Boring M. ALA-PDT and blue light therapy for hidradenitis suppurativa. J Drugs Dermatol. 2004 Jan-Feb 2004;3(1 Suppl):S32-5. 52. Sotiriou E, Apalla Z, Maliamani F, Ioannides D. Treatment of recalcitrant hidradenitis suppurativa with photodynamic therapy: report of five cases. Clinical and Experimental Dermatology. Oct 2009;34(7):e235-e236. doi:10.1111/j.1365- 2230.2008.03094.x 53. Lapins J, Sartorius K, Emtestam L. Scanner- assisted carbon dioxide laser surgery: A retrospective follow-up study of patients with hidradenitis suppurativa. Journal of the American Academy of Dermatology. Aug 2002;47(2):280- 285. doi:10.1067/mjd.2002.124601 54. Orringer JS, Voorhees JJ, Hamilton T, et al. Dermal matrix remodeling after nonablative laser therapy. J Am Acad Dermatol. Nov 2005;53(5):775-82. doi:10.1016/j.jaad.2005.07.052 SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 611 Table 1. Characteristics of included studies (n=40) Author, year Location Study design, LOE Intervention N# Mean age (±SD/range ) F: M Key findings Abdel Azim, 2018 Egypt RCT^ (1) Nd:YAG CO2+Nd:Y AG 20 29.7 (5) 11:9 Higher satisfaction and lower recurrence rates using combined CO2 and Nd:YAG Agut- Busquet, 2016 Spain Case series (3) PDT 7 28.9 3:4 Good results using PDT with intralesional MB Andino Navarrete, 2014 Chile Case series (3) PDT 5 26 (5) 4:1 5-ALA and 635nm light improved quality of life and reduced disease severity Belotto, 2013* Brazil Case series (3) PDT 5 NS 5:0 PDT improved inflammation and drainage Braunberg er, 2018* USA Case series (3) CO2 38 37.5 NS CO2 laser excision is a safe and effective treatment Bu, 2017 China Case series (3) PDT 7 24.4 0:7 Surgery combined with PDT improved DLQI and VSS scores Calzavara- Pinton, 2013 Italy Case series (3) PDT 6 34 (10.9) 5:1 MAL-PDT was effective and well tolerated Crocco, 2015 Brazil Case series (3) CO2 3 29.3 2:1 CO2 laser effective in Hurley III HS Darlymple, 1987 UK Case series (3) CO2 6 NS 5:1 CO2 laser was effective with minimal scarring Esposito, 2020 Italy Case series (3) PEHT 11 15.7 9:2 PEHT was effective with low recurrence rates Fabbrocini , 2018 Italy Case series (3) Diode laser 20 26.6 (7.84) 14:6 1064nm intralesional diode laser reduced Sartorius score and DLQI, increased HiSCR Fadel, 2015 Egypt RCT^ (1) PDT 10 27.1 (5.09) 7:4 Significant reduction in HS- LASI with PDT Finley, 1996 USA Case series (3) CO2 7 (20-46) NS CO2 laser is effective with low recurrence rates Giacaman, 2019* Spain Case series (3) PDT 8 NS 43:34 Adalimumab and PDT decreased lesions and pain Gold, 2004 USA Case series (3) PDT 4 27.8 (19- 46) 4:0 ALA-PDT is effective in HS patients who did not respond to medical therapy Grimstad, 2019 Norway Case series (2) CO2 156 39.3 (9.91) 191:6 7 Better response with surgical versus medical treatments. CO2 laser was most effective. Hazen, 2010* USA Case series (3) CO2 61 38.5 (21- 73) 42:19 CO2 laser excision and marsupialization is effective for persistent or late-stage HS Highton, 2011 UK Case series (3) IPL 17 34 (17-50) 14:3 IPL reduced Sartorius scores compared to control with good patient satisfaction Jain, 2012 India Case series (3) CO2 Nd:YAG 4 (30-40) 4:0 Deroofing with CO2 laser combined with Nd:YAG was effective with no recurrence Lapins, 1994 Swede n Case series (3) CO2 24 36 (22-57) 21:3 CO2 laser was effective for patients with chronic HS with low recurrence rates Lapins, 2002 Swede n Case series (3) CO2 34 33.9 (11.0/15- 55) 31:3 Scanner-assisted CO2 laser ablation improved scarring and had high patient satisfaction Madan, 2008 UK Case series (3) CO2 9 39 (27-52) 8:1 CO2 laser was an effective treatment for patients with recalcitrant HS SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 612 Mahmoud, 2010 USA RCT^ (1) Nd:YAG 22 41 (19-72) 19:3 Nd:YAG + topical BPO & clindamycin better than topical BPO & clindamycin alone Mikkelsen, 2015 Denma rk Case series (3) CO2 58 37.8 (21- 54) 48:10 CO2 laser treatment effective for recurrent HS Naouri, 2020 France RCT^ (1) Nd:YAG 31 NS NS Nd:YAG laser for hair removal has no effect on disease flares Passeron, 2009 France Case series (3) PDT 4 NS NS PDL-PDT was not effective in treating HS Piccolo, 2014 Italy Case series (3) IPL 2 32 (26-38) 1:1 IPL completely resolved HS lesions Rodriguez -Prieto, 2013 Spain Case series (3) PDT 3 47 (36-62) 0:3 No recurrence after ALA-PDT Rucker Wright, 2009 USA Case series (3) Nd:YAG 20 NS NS Nd:YAG laser reduced HS- LASI scores Shareef, 2011 UK Case series (3) PUVA 13 35 (25-66) 11:2 PUVA is an effective treatment in some patients Sotiriou, 2009 Greece Case series (3) PDT 5 33.6 (25- 43) 2:3 No significant improvement after ALA-PDT Strauss, 2005 UK Case series (3) PDT 4$ NS NS No significant improvement after ALA-PDT Suarez- Valladares , 2018* Spain Case series (3) PDT 5 NS NS Resolution with no recurrence after ALA-PDT Suarez- Valladares , 2017 Spain Case series (3) PDT 38 36 (30-44) 18:20 Complete response in most patients after ALA-PDT Theut Riis, 2018 Denma rk Case series (3) IPL 25 39.2 (10.9/17- 63) 25:0 IPL effective as an adjuvant treatment in a subset of patients Valladares -Narganes , 2015 Spain Case series (3) PDT 27 30.3 (19- 62) 11:16 ALA-PDT effective in most patients and improved Sartorius score Vilarrasa, 2019* Spain Case series (3) PDT 28 46 13:15 ALA-PDT improved DLQI and pain Vossen, 2018 The Netherl ands Case series (3) Nd:YAG 15 34.1 (10.1) 5:10 Nd:YAG reduced number of flares and reduced disease severity Wilden, 2019 Germa ny RCT (1) IPL + radiofrequ ency 41 38 (23-57) 31:12 IPL and radiofrequency reduced lesion count and DLQI compared to either treatment alone Xu, 2011 USA RCT^ (1) Nd:YAG 19 37 (23-54) 16:3 Nd:YAG improved HS-LASI score Zhang, 2016 China Case series (3) PDT 3 (17-38) 0:3 ALA-PDT ineffective for late- stage HS ALA: aminolevulinic acid, BPO: benzoyl peroxide, CO2: carbon dioxide, DLQI: Dermatology Life Quality Index, F: female, HiSCR: Hidradenitis Suppurativa Clinical Response, HS: hidradenitis suppurativa, HS-LASI: Hidradenitis Suppurativa Lesion, Area, and Severity Index, IPL: intense pulsed light, LOE: Level of evidence, MAL: methyl aminolevulinate, M: male, Nd:YAG: neodymium-doped yttrium aluminum garnet, NS: not specified, PDL: pulsed dye laser, PDT: photodynamic therapy, PEHT: pediatric endoscopic HS treatment, PUVA: psoralen and ultraviolet A, RCT: randomized controlled trial * Abstract only # Number of participants included in analysis $ 2 participants completed the study ^ Randomized within-patient controlled trial Key to evidence-based support: (1) prospective controlled trial; (2) retrospective study or large case series; (3) small case series or individual case reports SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 613 Table 2. Summary of treatment outcomes by phototherapy intervention for HS Light and Laser-based Treatment Modality (pooled n) % Patients with Any Response (n) % Adverse Events (n) Laser surgery: CO2 laser, CO2 + Nd:YAG, PEHT, intralesional diode laser (431) 80 (344) 25 (105/424) CO2 (396) 79 (311) 26 (103/393) CO2 + Nd:YAG (4) 100 (4) NR PEHT (11) 100 (11) 0 (0/11) Intralesional diode laser (20) 90 (18) 10 (2/20) Field treatment: Nd:YAG laser, IPL, diode (101) 71 (84) 18 (24/134) PDT (169) 73 (124) 36 (23/64) PUVA (13) 69 (9) 15 (2/13) n - number of patients with outcomes reported CO2: carbon dioxide, IPL: intense pulsed light, Nd:YAG: neodymium-doped yttrium aluminum garnet, PDL: pulsed dye laser, PDT: photodynamic therapy, PEHT: pediatric endoscopic HS treatment, PUVA: psoralen and ultraviolet A SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 614 Table 3. Results of included studies examining multiple outcome measures on hidradenitis suppurativa Author , Year N Mean age (±SD/ range) Intervention Outcome measure Mean before (±SD) Mean after (±SD) Delta Conclusion Abdel Azim, 2018 20 29.7 (±5) Nd:YAG and combined CO2/Nd:YA G PGA CO2/Nd:YAG: 20.6 Nd:YAG: 20.4 CO2/Nd:YAG: 16.9 Nd:YAG: 24.1 CO2/Nd:YAG: -3.7 Nd:YAG: 3.7 CO2+Nd:YAG superior to Nd:YAG alone. Combined treatment had a lower rate of recurrence and higher patient satisfaction. VAS patient satisfaction N/A CO2/Nd:YAG: 24; Nd:YAG: 17 N/A Agut- Busq uet, 2018 7 28.9 I-PDT VAS 4.6 (±1.4) N/A N/A I-PDT is more effective for HS Hurley stage II than stage III. At 6 months, 5/7 patients had no recurrence. DLQI 9.4 (±3.9) 2.2 (±2.1) -7.2 PGA 3 (±2.2) N/A N/A US assessments Large transverse diameter Reduced diameter in treated lesions N/A Andin o Navar rete, 2014 5 26 (±5) PDT (5- ALA; 635nm light) Sartorius 35.4 (±4.98) 18.2 (±8.11) -17.2 PDT improved QOL and reduced severity of disease. DLQI 28.8 (±2.68) 7.49 (±2.79) -21.31 VAS 3 (±0) 0.8 (±0.45) -2.2 Belott o, 2013 5 N/A PDT# Inflammation, drainage, erythema, edema N/A Reduced drainage and inflammation in 60%; partial reduction in 40%. N/A PDT improves inflammation and drainage Braun berge r, 2018 38 37.5 CO2 laser Healing time in smokers N/A Smokers: 6 months Non-smokers: 6 months N/A After CO2 excision – smoking did not affect healing time but diabetics had a prolonged healing time. 3 patients experienced recurrence at a mean of 6 months post procedure. Healing time in diabetics N/A Diabetics: 7.3 months Non-diabetics: 5.4 months N/A Recurrence N/A 3 patients N/A Bu, 2017 7 24.4 Surgery combined with PDT Healing time N/A 29.4 days N/A Surgery in combination with PDT improved DLQI. No recurrence. Advantage of faster healing and less scaring. Recurrence N/A No recurrence N/A DLQI 24.1 (±4.3) 5 months post treatment: 4.9 (± 2.8) -19.2 VSS N/A 4.6 (±2.4) N/A Calza vara- Pinto n, 2013 6 34 (± 10.9) MAL-PDT Clinical response N/A No/poor response: 17%; Moderate: 50%; Marked: 33% N/A 2/6 patients had marked improvement, 3 had moderate improvement, and 1 had no/poor response with MAL- PDT treatment. Local reaction N/A Absent: 17%; Moderate: 83%; Marked: 0% N/A Cosmesis N/A 33% N/A Crocc o, 2015 3 29.3 CO2 laser Clinical response Patient 1: abscesses in axilla Patient 2: abscesses in axillary, inframammary and inguinal regions Patient 3: abscesses in axilla & groin Patient 1: successful treatment Patient 2: successful treatment Patient 3: successful treatment N/A CO2 laser effective in Hurley III HS. Darly mple, 1987 6 (20- 43) CO2 laser Wound healing N/A 3-7 weeks N/A Patients reported limited scarring. All patients were disease free at 9 months to 3 years follow up. All Recurrence N/A None N/A SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 615 recurrences were in untreated areas. Espos ito, 2020 11 15.7 Pediatric endoscopic hidradenitis treatment (PEHT) Postoperative VAS 0.7 N/A N/A PEHT was effective with good patient satisfaction and results. Time to restart work/school N/A 1.8 days N/A Wound healing time N/A 32.5 days N/A Recurrence N/A 2 (18%) patients developed lesions in untreated locations N/A Fabbr ocini, 2018 20 26.6 (± 7.84) Diode laser 1064nm Sartorius 28.6 (±13.0) 19.8 (±12.3) -8.8 Laser treatment reduced Sartorius score, improved HiSCR, and reduced DLQI. PGA 10 (50%) mild; 10 (50%) moderate N/A N/A HiSCR N/A 6 (30%) not achieved; 14 (70%) achieved N/A Clinical response N/A 1 (5%) complete response; 7 (35%) good response; 10 (50%) partial response; 2 (10%) no response N/A Fadel, 2015 10 27.1 (±5.09 ) PDT (Niosomal methylene blue (NMB) vs. free methylene blue (FMB) as a photosensiti zer to IPL) Photos Patient 1: lesions in right axilla Patient 2: groin lesions in a female Patient 3: extensive fibrosis in axilla Patient 4: Hurley stage 3 Patient 1: complete clearance of lesions Patient 2: improvement in lower part of lesion Patient 3: mild improvement Patient 4: moderate improvement N/A Photosensitization with NMB was more effective compared to photosensitization with FMB. HS-LASI NMB: 14.9 (±6.6); FMB: 14.0 (±7.2) NMB: 3.6 (±3.4); FMB: 7.9 (±5.6) NMB: -11.3; FMB: -6.1 Reduction in percentage of lesions N/A NMB: 77.3 (±18.9); FMB: 44.1 (±28.2) N/A Finley , 1996 7 (20- 46) CO2 laser Healing time N/A 6.6 weeks (±1.9) N/A CO2 laser treatment with healing by second intention was effective for HS. All patients were satisfied with results and reported good cosmesis. Recurrence N/A 1 patient 8 months post procedure N/A Giaca man, 2019 8 38 (media n) I-PDT Lesions N/A Decrease in lesions N/A There was a decrease in inflammatory lesions and pain. Pain N/A Decrease in pain N/A Gold, 2004 4 27.8 (19- 46) ALA-PDT and blue light Lesions Patient 1: lesions in axillae and inguinal area Patient 2: lesions in axillae Patient 3: lesions in inguinal areas Patient 4: lesions in inguinal area Patient 1: 75% clearance of lesions Patient 2: 75% clearance of lesions Patient 3: complete clearance of lesions Patient 4: 75% clearance of lesions N/A ALA-PDT and blue light phototherapy is an effective treatment for patients who did not respond to medical therapy. SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 616 Grims tad, 2019 15 6 39.3 (±9.91 ) CO2 laser, CO2 laser and topical clindamycin, CO2 laser and systemic antibiotic Sartorius score CO2 laser (n=156): 57; CO2 laser and topical clindamycin (n=5): 85; CO2 laser and systemic antibiotic (n=1): 123 N/A CO2 laser (n =156): -33; CO2 laser and topical clindamycin (n=5): -36; CO2 laser and systemic antibiotic (n =1): -87 CO2 laser was the most effective intervention studied. Almost half of patients treated with a combination of surgical and medical treatments had a significant improvement in Sartorius score. DLQI CO2 laser (n=156): 14; CO2 laser and topical clindamycin (n=5): 14; CO2 laser and systemic antibiotic (n=1): 13 N/A CO2 laser (n =156): -5; CO2 laser and topical clindamycin (n=5): -6; CO2 laser and systemic antibiotic (n =1): 0 Hazen , 2010 61 38.5 (21- 73) CO2 laser excision and marsupializa tion Recurrence of disease N/A Recurrence in 2 patients. Average of 4.1 years without recurrence in treated areas (range of 1-17 years). N/A CO2 laser excision & marsupialization effective therapy for persistent or late- stage HS (when scarring and sinus tract formation present). Comfort/ patient satisfaction N/A Treatments well tolerated in all patients. N/A Healing time N/A 8.8 weeks N/A Hight on, 2011 17 34 (17- 50) IPL (Harmony laser; 2x/week for 4 weeks on one area vs contralateral side not treated - served as control) Sartorius score N/A 3 months post treatment: -56%. 6 months: -44%. 12 months: - 33%. Control side - 3 months: -10%. 6 months: -10%. 12 months: 3%. Significant reduction in HS exam score on treated side (p<0.001). Significant difference between treated and control sides (p<0.001). Reduction in severity of HS with IPL. Mean examination score was improved and maintained at 12 months. Improvement was also reported by independent analysis of clinical photographs. Patients reported high levels of satisfaction with treatment. Treated side had significant reduction in Sartorius score maintained at 12 months (p=0.001). Patient satisfaction N/A Treatment side Disease clearance: 1 patient Excellent results: 2 patients Good results: 10 patients 4 patients: fair results Control side: No change: 15 patients Slight improvement: 1 patient Slight decline: 1 patient N/A Jain, 2012 4 (30- 40) Nd:YAG and CO2 laser Recurrence of disease N/A No recurrence N/A Deroofing with CO2 laser combined with Nd:YAG laser is effective in treating HS, with no recurrence observed up to 3 years. SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 617 Lapin s, 1994 24 36 (22- 57) CO2 laser with healing by secondary intention Recurrence of disease N/A Recurrence: 2 No recurrence: 22 N/A CO2 laser treatment with secondary intention for patients with chronic HS is beneficial, safe, and quick, leaving patients with good cosmetic and functional results. Healing time N/A 4 weeks (3-5 weeks) N/A Scarring/cosm etic appearance N/A All patients satisfied with scar appearance. N/A Patient satisfaction N/A Patients found this method favourable, willing to repeat procedure if required. N/A Lapin s, 2002 34 (±11.0 /15- 55) Scanner- assisted CO2 laser ablation Recurrence N/A Recurrence: 4 No recurrence: 30 N/A CO2 laser with scanner is a fast and efficient treatment of HS, with satisfactory cosmetic and functional results. Healing time N/A 4 weeks (3-5 weeks) N/A Pain in post- op period (Scale from 0- 3) N/A Classified as 3: 4 Classified as 2: 15 Classified as 1: 9 Classified as 0: 6 N/A Patient satisfaction N/A Condition better than pre surgery: 31 patients Hardly changed: 2 patients Worse: 1 patient N/A Mada n, 2008 9 39 (27- 52) CO2 laser excision (prophylactic oral antibiotics for 2 weeks post-op) Recurrence of disease N/A No recurrence: 6 Active HS at untreated sites adjacent to treated sites: 2 N/A CO2 laser is an effective treatment for patients with recalcitrant HS, with patients reporting high satisfaction scores. Patient satisfaction N/A 8.5/10 (range of 7-10) N/A Wound healing time N/A 2 weeks (range of 1-4) N/A Mahm oud, 2010 22 41 (19- 72) Nd:YAG laser (combined with topical benzoyl peroxide wash and clindamycin lotion; benzoyl peroxide and clindamycin alone used as control) Modified Sartorius score (HS Lesion Area and Severity Index) At baseline for all sites combined: 31 (SD: 14.9) All control sites combined: 29 (SD:13.2) At 6 months Treated sites: 7.6 (SD: 4.1) Mean for all control sites: 19.9 (SD: 10.9) Average improvement over all anatomic sites was 72.7% on laser treated side and 22.9% on control side (p< 0.05). Nd:YAG laser & topical benzoyl peroxide + clindamycin are associated with progressive improvement of HS lesions, and are more effective than topical benzoyl peroxide + clindamycin alone. Overall high level of patient satisfaction with treatment. Patient satisfaction - Pain associated with HS N/A Pain significantly less: 77% Moderately less: 15% Pain unchanged: 8% N/A Patient satisfaction N/A Generally satisfied: 55/58 patients N/A Mikke lsen, 2015 58 37.8 (21- 54) CO2 Patient satisfaction N/A 94.8% (n=55/58) of patients reported a small (n=11) or great improvement (n=44) N/A CO2 laser surgery is an effective treatment for symptomatic HS lesions. Patient satisfaction is high despite a moderate number of recurrences. SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 618 Recurrence of disease N/A 29.3% (n=17/58) of patients reported recurrence of disease in treated areas N/A Naour i, 2020 31 Not specifi ed Nd:YAG laser (4 treatments at 6 week intervals) Inflammatory lesion count Week 0 Untreated: 5.86 (±6.29). Treated: 5.89 (±4.68). Week 22 Untreated: 1.69 (±15.01) Treated: -1.25 (±10.77) Week 30 Untreated: -0.81 (±6.08). Treated: -2.56 (±4.22). Weeks 0-30 Untreated: - 6.67. Treated: -8.45. The laser had no impact on disease recurrence. The effectiveness of laser hair removal in reducing the amount of inflammation lesions decreases with time. Proportion of responders to Hidradenitis Suppurativa Clinical Response (HiSCR) N/A 1-month post tx Treated side: 73.7% Control side: 52.6% (P= 0.29). 3-month post tx Both treated and control sides: 52.6% No significant difference in number of flares between treated and untreated sites at 1 and 3- month follow- up Passe ron, 2009 4 Not specifi ed PDL-PDT (ALA, only one side of axilla or groin was treated – the other used as control) Sartorius score PDL-PDT side: 11.25 Control side: 11 At 1 month PDL-PDT side: 8.25. Control side: 13 At 3 months PDL-PDT side: 9 Control side: 8.67 Baseline to month 3 PDL-PDT side: -2.25 Control side: - 2.33 PDL-PDT not effective in treating HS. VAS N/A Pain was high during treatment. Mean: 8 (6-9) N/A Piccol o, 2014 2 32 (26- 38) IPL (6 sessions) Sartorius score 30 (24-36) N/A N/A HS lesions were completely resolved, along with achieving hair removal. Recurrence N/A HS pustular papules resolved post treatment N/A Rodri guez- Prieto , 2013 3 47 (36- 62) PDT (intralesional 5-ALA and irradiated with diode laser) Recurrence of disease N/A Patient 1: No recurrence at 9 months Patient 2: No recurrence after 14 months Patient 3: resolution of symptoms after 7 months N/A No recurrence post intralesional PDT in all 3 patients. Share ef, 2011 13 35 (25- 66) PUVA (bath) DLQI 16 (11-26) N/A N/A Bath PUVA is possibly an effective treatment modality for some people with HS. Disease clearance N/A Clear/near clear: 5 patients; moderate clearance: 4; no- minimal: 4 N/A Sotiri ou, 2009 5 33.6 (25- 43) PDT (topical 5- ALA) Sartorius score 18.8 17.2 -1.6 No significant improvement post treatment. VAS – disease severity and pain 2.4 2.1 -0.3 DLQI N/A N/A Reduction in mean of 6.4% 4 PDT (topical ALA) Sartorius score 17.8 23.3 5.5 SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 619 Strau ss, 2005 Not specifi ed VAS – disease severity 8.1 7.1 -1 No significant improvement post treatment. Worsening symptoms for 2 patients. VAS - pain 7 5.3 -1.7 Suare z- Vallad ares, 2018 5 Not specifi ed PDT (intralesional ALA) Qualitative descriptions by investigators N/A All patients achieved a complete response in the treated lesion N/A Resolution of disease in 3/3 patients. No recurrence noted at follow up. Suare z- Vallad ares, 2017 38 36 (30- 44) I-PDT (5-ALA) Response to treatment N/A Complete response: 29 patients Persistence: 8 patients Recurrence: 1 patient N/A A complete response (no lesions or symptoms) rate of 76.3%. I-PDT is a potential effective alternative treatment to HS. DLQI Median = 10 (7-17) Median = 1 (0- 2.25) -9 HSS Median = 28.5 (11.75-38.5) Median = 0 (0- 45) -28.5 Theut Riis, 2018 25 39.2 (SD 10.9/1 7-63) IPL Patient reported disease activity N/A Reduced disease activity: 13/25 patients N/A IPL can be used as an adjuvant treatment for HS - in those with mild to moderate disease with minimal scar tissue. Hair reduction N/A Effect on hair in 17/25 patients N/A Vallad ares- Narga nes, 2015 27 30.3 (19- 62) I-PDT (5- ALA) Modified Sartorius score 20.67 8.81 -11.86 21/27 patients had either a good or complete response to treatment. Intralesional application of PDT allows the light to reach various depths with the lowest amount of energy needed. It may be an effective treatment for HS. Response to treatment N/A Complete response: 10 (37%) Good response: 11 (41%) Partial response: 5 (19%) N/A VAS - pain N/A Severe pain (9): 1 Moderate (6-9): 4 Low (<6): 22 N/A Vilarr asa, 2019 28 46 PDT (topical 5-ALA) DLQI & EVA (pain visual scale) N/A N/A All patients showed improvement in DLQI & EVA All patients improved in DLQI and EVA scores 8 weeks post last treatment session. Ultrasound showed a resolution in the lesions of 13 patients, partial resolution in 12 patients, and poor in 3. Ultrasound N/A Resolution of lesions: 13 patients Partial resolution: 12 patients Poor: 3 patients N/A Vosse n, 2018 15 34.1 (10.1) Nd:YAG laser (hair removal on patients with mild HS) Number of HS flares/month (Questionnaire ) <1 flare: 4 patients 1 flare: 2 patients 2 flares: 1 patient 3 flares: 3 patients >3 flares/continuo us inflammation: 5 patients <1 flare: 8 patients 1 flare: 0 2 flares: 3 patients 3 flares: 3 patients >3 flares/ continuous inflammation: 1 patient Decrease in number of monthly flares (p=0.019). Laser hair removal can be used to prevent the progression of disease. Results include decrease in the number of monthly flares, average HS disease severity was significantly lower post treatment (NRS 6.4 ± 2.8 versus NRS 3.6 ± 3.5). Overall treatment satisfaction was rated with a NRS score of 6.7 ± 2.4. 2/3 patients would recommend the treatment. NRS disease severity (0-10) NRS 6.4 (±2.8) NRS 3.6 (±3.5) p= 0.01 -2.8 NRS overall treatment satisfaction (0- 10) N/A NRS 6.7 (±2.4) N/A SKIN November 2021 Volume 5 Issue 6 Copyright 2021 The National Society for Cutaneous Medicine 620 DLQI: Dermatology Life Quality Index; HSS: Hidradenitis severity score; MAL: methyl amino; N: number of participants; PDT: photodynamic therapy I-PDT: intralesional photodynamic therapy PUVA: psoralen plus ultraviolet A; US: ultrasonographic; VAS: visual analogue scale; VSS: Vancouver Scar Scale; QOL: quality of life MCID: minimum clinically important difference NRS 30 – 30% reduction to baseline numerical rating score\ # tetracycline used as a photosensitizer combined with 600nm red light Wilde n, 2019 13 38 923- 57) IPL and radiofrequen cy (RF) Active lesions count N/A N/A IPL: 0.8 RF group: -0.4 IPL+RF group: -1.3 Whole cohort on crossover to IPL+RF for 24 weeks: -3.6 (p=0.001). IPL + RF is a promising treatment for HS, increasing in effect over time and without severe side effects. DLQI N/A N/A IPL group: -1.3 RF group: -5.1 IPL+ RF group: -6.6 (p=0.025). Whole cohort on crossover to IPL+RF for 24 weeks: -5.2 (p=0.003). Wollin a, 2004 17 (29- 41) Transdermal CO2 Clinical response N/A N/A Improvement of granulation and reduction of discharge and malodor 1-week post treatment Xu, 2011 19 37 (23- 54) 1064nm Nd:YAG laser Lesion Area and Severity Index (LASI) N/A N/A All sites: -31.6% (p<0.05) Axillary sites: -24.4% (p=0.08) Inguinal site: -36.8% (p=0.001). The percentage change in modified HS-LASI score after 2 months was –31.6% (p<.001) averaged over all anatomic sites. HS-LASI scores trended down from baseline to 1 month and 2 months after treatment for both axilla and inguinal sites. Zhang , 2016 3 (17- 38) PDT (ALA) DLQI 26.67 (1.15) Session 1: 24.67 Session 2: 24.33 Session 3: 24.33 N/A No improvement for late-stage HS.