Dermatology: Practical and Conceptual Original Article | Dermatol Pract Concept. 2025;15(1):4887 1 Clinical and Onychoscopy Patterns In Fingernail Onychomycosis – A Study By The International Dermoscopy Society “Trichoscopy and Onychoscopy” Task Force Matilde Iorizzo1, Bianca Maria Piraccini2,3, Aurora Alessandrini2,3, Francesca Bruni2,3, Laura Vollono4, Francesca Pampaloni2,3, Nilton Gioia Di Chiacchio5,6, Nilton Di Chiacchio6, Juan Jimenez-Cauhe7, Chander Grover8, Zoe Apalla9, Asmahne Souissi10, Awatef Kelati11, Eirini Kyrmanidou9, Elizabeth Lazaridou9, Michela Starace2,3 1 Private Dermatology Practice, Lugano/Bellinzona, Switzerland 2 Dermatology - IRCCS Policlinico San’t Orsola, Bologna, Italy 3 Department of Experimental, Diagnostic and Specialty Medicine, Alma Mater Studiorum, University of Bologna, Bologna, Italy 4 Private Dermatology Practice, Rome, Italy 5 Dermatology Department, Medical School of ABC, São Paulo, Brazil 6 Dermatology Department, Hospital do Servidor Público Municipal de São Paulo, São Paulo, Brazil 7 Dermatology Department, Hospital Universitario Ramon y Cajal, IRYCIS, Universidad de Alcala, Madrid, Spain 8 Department of Dermatology and STD, University College of Medical Sciences and GTB Hospital, Delhi, India 9 Second Department of Dermatology, Aristotle University School of Medicine, Thessaloniki, Greece 10 Department of Dermatology, La Rabta Hospital, Tunis, Tunisia & Faculty of Medicine of Tunis, University of Tunis El Manar, Tunis, Tunisia 11 Dermatology Department, University Hospital Cheikh Khalifa, Casablanca, Morocco & University Hospital Mohammed VI, Faculty of Medicine, Mohammed VI University of Health and Sciences (UM6SS), Casablanca, Morocco Key words: Onychomycosis, Fingernail, Dermoscopy, Onychoscopy, Onycholysis Citation: Iorizzo M, Piraccini BM, Alessandrini A, et al. Clinical And Onychoscopy Patterns In Fingernail Onychomycosis – A Study By The International Dermoscopy Society “Trichoscopy And Onychoscopy” Task Force. Dermatol Pract Concept. 2025;15(1):4887. DOI: https:// doi.org/10.5826/dpc.1501a4887 Accepted: October 11, 2024; Published: January 2025 Copyright: ©2024 Iorizzo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Matilde Iorizzo, MD PhD, Private Dermatology Practice, Viale Stazione 16 – 6500 Bellinzona (Switzerland). E-mail: matildeiorizzo@gmail.com 2 Original Article | Dermatol Pract Concept. 2025;15(1):4887 Introduction Onychomycosis is one of the most common nail diseases and describes the invasion of the nail by fungi, mainly an- thropophilic dermatophytes including Trichophyton rubrum and Trichophyton mentagrophytes var. interdigitalis [1,2]. Yeasts and molds are less frequent culprits and often require rigorous criteria for being acknowledged as the responsible agents [3]. True Candida onychomycosis is a rare condition usually affecting immunocompromised individuals. Candida is in fact mainly a colonizer, a secondary phenomenon, of other diseases [4] such as chronic paronychia or idiopathic onycholysis [5]. Mixed infections are also a possibility when dealing with onychomycosis [6]. According to the literature, fingernail onychomycosis is 7 times less frequent than toenail onychomycosis [7]. Fin- gernail onychomycosis is commonly associated with toenail onychomycosis in the “two-feet one-hand syndrome” where the fungi invade both soles and 1 palm and all toenails and the fingernails of 1 hand. When not associated with toenail involvement, onychomycosis of the fingernails is a rare and often misdiagnosed and mistreated condition, especially when limited to 1 or 2 nails. Many nail dystrophies in fact can mimic fingernail onychomycosis, due to the fact that the nail apparatus has a limited repertoire of reaction patterns [8-11]. Also, clinical variants of fingernail onychomycosis have not been described much in detail as for toenail ony- chomycosis [12]. Different clinical variants usually depend on the way and to the extent to which fungi colonize the nail unit: (a) Distal and lateral subungual onychomycosis (DLSO) where fungi invade the nail through the hypony- chium and spread proximally; (b) white superficial onycho- mycosis (WSO) where fungi colonize the dorsal nail plate, forming white opaque patches; (c) proximal subungual on- ychomycosis (PSO) where fungi penetrate the nail via the proximal nail fold and localize under the proximal nail plate causing proximal leukonychia and possible acute periun- gual inflammation; (d) endonyx onychomycosis (EO) where fungi colonize the medial part of the nail plate with spar- ing of the nail bed; and (e) total dystrophic onychomycosis (TDO) resulting from long-standing DLSO or PSO, and pre- senting with a diffusely discolored, friable and invaded nail plate [13,14]. Onychomycosis is an important infection to rule out because its management can be challenging, especially due to the slow nail growth, treatment resistance, scarce compli- ance to treatments, drug to drug interactions, and onset of possible adverse events. For this reason, when onychomyco- sis is suspected, laboratory confirmation should always be performed. Toenail onychomycosis has been extensively de- scribed and clinicians generally know when they are dealing with a mycotic infection, thanks also to the well-known on- ychoscopy patterns: jagged edge of the proximal margin of the onycholytic area with sharp structures (spikes) directed to the proximal nail fold, white-yellow longitudinal striae within the onycholysed nail plate, parallel bands of varying colors (aurora borealis) and a ruin like appearance of the subungual hyperkeratosis [15-18]. This is less true for onychomycosis limited to the finger- nails. In such cases, the literature is scarce, and the subtle Introduction: Onychomycosis is one of the most common nail diseases. Fingernail onychomycosis is significantly less frequent than toenail onychomycosis and it is often misdiagnosed due to its subtle clinical presentations. Objectives: We sought to analyze the clinical and onychoscopic features of culture-proven cases of fingernail onychomycosis in adult and pediatric patients. Methods: Medical records of 120 patients with onychomycosis limited to the fingernails were collect- ed and analyzed across several dermatological centers (Italy, Switzerland, Spain, Greece, Brazil, India, Morocco, Tunisia). Data collected included age, sex, affected hand, affected fingernails, isolated fungal microorganism, clinical, and onychoscopic signs. Results: A total of 341 fingernails were analyzed. The most commonly affected hand was the right one, and the most frequently affected digits were the second and third. The mean number of affected digits per patient was 2.84. Cultures identified Trichophyton rubrum in 54 cases, T. mentagrophytes var. interdigitalis in 20 cases, Aspergillus spp. in 8 cases, Candida spp. in 31 cases, and various other fungi in the remaining cases. Major clinical and onychoscopic features observed included onycholysis, subungual hyperkeratosis, leukonychia, chromonychia and absence of the cuticles. On the basis of all findings, 4 main types of fingernail onychomycosis were identified. Conclusions: Fingernail onychomycosis presents with distinct clinical and onychoscopy characteris- tics that can overlap with other nail conditions. Dermoscopy enhances diagnostic accuracy, but myco- logical confirmation is mandatory for a definitive diagnosis. ABSTRACT Original Article | Dermatol Pract Concept. 2025;15(1):4887 3 clinical presentation makes diagnosis more challenging than usual, leading to diagnostic delays. Objectives The objective of this study was to describe the clinical and onychoscopy features of culture-proven cases of fingernail onychomycosis in adult and pediatric patients. Methods Medical records of 120 patients affected with onychomy- cosis limited to the fingernails were collected and analyzed. All patients and caregivers had agreed to sign a writ- ten informed consent for publication of their case details. The ethical principles for human studies as outlined in the Declaration of Helsinki were followed and attested. The study spanned across several dermatological centers (Italy, Switzerland, Spain, Greece, Brazil, India, Morocco, Tunisia), each researcher contributing anonymized patient data to the collective analysis. Inclusion criteria comprised male and fe- male patients, adults and children, diagnosed with isolated fingernail onychomycosis (no other nail dystrophy or disease associated), not on any treatment at the time of the diagnosis for the previous 6 months. The 6-month timeframe was se- lected according to the nail plate growth rate (3 mm/month for fingernails and 1.5 mm/month for toenails), ensuring ad- equate nail plate regeneration not influenced by treatment for a correct diagnosis. Each patient had their diagnosis con- firmed by direct microscopy with 40% potassium hydrox- ide and culture. Exclusion criterion was the involvement of toenails with onychomycosis and other diseases affecting the nails. Data collected included age, sex, affected hand, affected fingernails, fungal microorganism isolated, clinical and onychoscopy signs. Data about a correlation between the localization of the infection and the dominant hand were, unfortunately, not collected. Clinical and onychoscopy pictures (magnification 10X), available for each case, were independently analyzed by each author. Statistical analysis was performed with IBM SPSS Statistics (Version 25.0: IBM Corp., 2017). Results Records of 120 patients (56 males and 64 females) with a mean age of 52 years (range 4 – 92) were analyzed for this study. Only 6 patients were younger than 18 years old, 3 males and 3 females, aged between 4 and 9 years. Fifty-three patients (44.2%) reported the infection on the right hand only, 37 patients (30.8%) on the left hand only and in 30 cases (25%) the infection was bilateral. A total of 341 fingernails were affected in our cohort. The mean number of affected digits per patient was 2.84 (range 1 – 10). The most common affected digits were the second and the third followed by the fourth and the first. The fifth digit was the less frequently affected. Culture revealed 54 cases of Trichophyton rubrum infection, 20 cases of T. mentag- rophytes var. interdigitalis, 1 case of T. verrucosum, 8 cases of Aspergillus spp (7 var. flavus and 1 var. niger), 2 cases of Alternaria, 1 case of Trichosporon, 1 case of Cladosporium, 1 case of Geotrichum, 1 case of Yarrowia lipolytica and 31 cases of Candida spp. Clinical and onychoscopy features de- tected on the nail plate, nail bed and periungual area are reported in Table 1. Each digit showed more than one sign and a single sign was not necessarily present in all fingers of a single patient. Regarding nail plate abnormalities, we observed Beau lines/onychomadesis, pitting, trachyonychia, crumbling, leu- konychia in different patterns, melanonychia, and chromon- ychia (colors other than brown and white, mainly yellow and orange). Regarding nail bed abnormalities, we observed ony- cholysis, subungual hyperkeratosis and splinter hemorrhages. Regarding nail fold abnormalities we observed paronychia, absence of the cuticles and periungual scaling. Onychoscopy allowed us to better characterize some clinical aspects. Sub- ungual hyperkeratosis, for example, was always minimal and Table 1. Clinical (C) and Onychoscopy (O) Signs Detected in Our Cohort of 120 Patients. Nail Matrix/Plate Abnormalities N (%) of Patients Presenting With This Sign Beau lines / onychomadesis (C) Pitting (C) (O) Trachyonychia (C) Crumbling (C) Leukonychia • Transverse (C) • Longitudinal (C) • Irregular spots (including punctate) (C) • Total (C) Melanonychia (C) (O) Chromonychia (C) (O) 23 (19.2%) 9 (7.5%) 19 (15.8%) 25 (20.8%) 32 (26.7%) 18 (15%) 49 (40.8%) 5 (4.2%) 17 (14.2%) 58 (48.3%) Nail bed abnormalities Onycholysis • Linear (O) • Jagged (O) Subungual hyperkeratosis (C) (O) Splinter hemorrhages (O) 48 (49.5%) 49 (50.5%) 90 (75%) 20 (16.6%) Nail folds abnormalities Periungual scaling (C) (O) Absence of cuticles (C) Paronychia (C) 27 (22.5%) 59 (49.2%) 38 (31.6%) 4 Original Article | Dermatol Pract Concept. 2025;15(1):4887 3. Superficial alterations type (Figure 1C) (11/120 – 9.2%) - nail plate surface changes are the predominant onycho- scopic feature in this type. It is characterized by pitting or trachyonychia, irregular spots of leukonychia, minimal onycholysis, minimal subungual hyperkeratosis, absence of the cuticle and periungual scaling. These findings can be associated with WSO and EO. 4. Crumbling type (Figure 1D) (25/120 – 20.8%) - destruc- tion of the nail plate is the predominant onychoscopic feature in this type. It is characterized by nail plate crum- bling, chromonychia, spots of leukonychia, nail bed hem- orrhages and absence of the cuticle. These findings can be associated with TDO. The association between types of fingernail onychomycosis and etiological fungal species were not statistically significant. However, the association between the fungal genera and few clinical and onychoscopic signs were found to be statistically significant: Beau lines/onychomadesis (P = 0.02) and parony- chia (P = 0.02) were more frequently observed in cases of in- fection by yeasts (Candida, Yarrowia and Trichosporon). Total leukonychia (P = 0.03), melanonychia (P = 0.04) and periungual edges of onycholysis were partly linear as well as jagged with spikes. Onychoscopy allowed us also to better identify the hem- orrhages and presence of melanonychia and chromonychia. On the basis of these findings, we could identify 4 main types of fingernail onychomycosis which are best described as follows: 1. Chaotic type (Figure 1A) (35/120 – 29.2%) - color changes are the predominant onychoscopic feature in this type. It is characterized by a combination of multiple features including leukonychia (transverse or irregular spots) with spiked pattern, chromonychia (green, brown, black), onycholysis and paronychia. This type can be as- sociated with distal subungual onychomycosis (DSO) or proximal subungual onychomycosis (PSO). 2. Subungual hyperkeratosis type (Figure 1B) (49/120 – 40.8%) - onycholysis is the onychoscopic predominant feature in this type. It is characterized by moderate to se- vere onycholysis with minimal jagged margins, subungual hyperkeratosis with minimal ruin aspect, xanthonychia, spots of leukonychia, and nail bed hemorrhages. This type can be associated with DSO and DLSO invasion. Figure 1. (A) Chaotic type. (B) Subungual hyperkeratosis type. (C) Superficial alteration type. (D) Crumbling type (×10 magnification). Original Article | Dermatol Pract Concept. 2025;15(1):4887 5 prevalent nail plate surface alterations (20.8% and 19.2% respectively). Beau lines/onychomadesis were more frequently observed in cases with infection by yeasts (Candida, Yarrowia and Trichosporon). Ramos-Pinheiro et al [19] described, as we did, the crumbling pattern with distal breakage, crumbling of the nail edge and subungual hyperkeratosis in 13.6% of cases. Apart from this paper, our study is the first to focus on such a feature in onychomycosis. It is to be noted that crumbling of the nail plate may also be a sign of severe psoriasis [20]. Pso- riasis is the disease that mostly goes in differential diagnosis with onychomycosis, besides the fact that the two diseases can coexist. According to recent reviews on onychoscopy of nail psoriasis, pitting, crumbling, leukonychia, onycholysis with minimal subungual hyperkeratosis, and periungual scaling are signs in common with the two diseases [21,22]. Psoriasis is however an inflammatory condition usually involving more than one digit even if a single digit psoriasis should always be considered in differential diagnosis. The presentation of fingernail onychomycosis with chro- monychia and periungual inflammation may mimic chronic paronychia and bacterial infection. Leukonychia (white dis- coloration) seems however to be the prevalent color in fin- gernail onychomycosis, while it is less frequently described in toenail onychomycosis, where yellow and brown are the most prevalent colors seen [16,23]. In our study total leukon- ychia was more frequently observed in cases of infection by molds (Aspergillus, Alternaria and Cladosporum) similarly to what is observed in toenail onychomycosis. The other clinical presentations of leukonychia had a different preva- lence in each type of fingernail onychomycosis, possibly re- lated to different modalities of fungal invasion. Leukonychia could be due to fungal colonies above (WSO) or within the nail plate (EO) and it might be also related to matrix inflam- mation as in PSO or TDO. Trauma usually play an import- ant role in the development of true leukonychia (any form) and fungal invasion can be considered a significant cause of trauma [24]. A clipping of the part of nail plate showing leu- konychia followed by PAS stain would be beneficial to bet- ter characterize this sign in presence of an onychomycosis. Larger prospective studies involving patients with fingernail onychomycosis could help confirm this finding. We could not collect data about the dominant hand of the patients; hence, a correlation between the localization of the infection and the dominant hand or about a specific trauma could not be made. It would be useful to collect this data in future studies to better evaluate any potential relationship between trauma and single digit onychomychosis [11]. Onychoscopy, though it has proven to be a reliable tool for a definitive diagnosis of toenail onychomycosis, is not that reliable in fingernail onychomycosis. According to the litera- ture, fingernail onychomycosis is a rare variant of onychomy- cosis that usually affects immunocompromised patients [4,25]. scaling (P = 0.002) were more frequently observed in cases of infection by molds (Aspergillus, Alternaria and Cladosporum). Finally, subungual hyperkeratosis (P = 0.03) and leukonychia with irregular spots (P = 0.01) were more frequently observed in cases of infection by dermatophytes (Trichophyton spp). Also, trachyonychia was more frequent in older (P = 0.02) and female (P = 0.04) patients, while pitting was more common in younger patients (p=0.01) and subungual hyperkeratosis in men (P < 0.001). No statistically significant association was found between any fungal agent and the number of digits af- fected, nor with the involvement of one or both hands. Conclusions Fingernail onychomycosis is an uncommon nail condition, especially when it presents as an isolated form and not asso- ciated with toenail onychomycosis. Its subtle clinical presen- tations may be sometimes atypical, often delaying diagnosis. While toenail onychomycosis, especially DLSO, typically presents with jagged margin of the onycholytic border, yellow discoloration with spikes, and yellowish subungual hyperker- atosis possibly with a ruin like aspect [16-18], its counterpart in fingernails present with a less obvious picture that is more often characterized by minimal nail bed hyperkeratosis, se- vere onycholysis, dystrophic nail plate and paronychia. Fingernails are constitutionally thinner than toenails and hands experience different degrees of trauma as compared to the feet. Fingernails are also much more in contact with water and detergents, explaining why onycholysis is more severe and subungual keratosis minimal in fingernail ony- chomycosis. It is also possible that subungual hyperkeratosis is periodically removed by patients with a sharp file, which in turn, promotes a mechanical worsening of the onycholy- sis. This is a procedure usually performed by females and this may explain why subungual hyperkeratosis was mostly found in males in our study. According to literature, linear onycholysis is typical of traumatic or idiopathic onycholysis [16-19]. As stated, we found it in a significant number of our cases, but it is unclear whether it started as such or if it occurred later due to frequent cleaning of the subungual space and contact with water and detergents. Of note, the number of cases presenting with linear onycholysis in our series mostly occurred in females (56.2%). Nail plate surface abnormalities of different degree and type were another common sign of fingernail onychomycosis in our study. Superficial alterations are instead not typical of toenail onychomycosis. Kayarkatte et al [17] also described surface abnormalities introducing the term “lamellar micro- splitting” for irregularly placed fine transverse splitting of the nail plate surface, best visualized with nonpolarized dermos- copy. We did not observe this sign in our patients, where crum- bling and Beau line/onychomadesis were instead the most 6 Original Article | Dermatol Pract Concept. 2025;15(1):4887 12. Elewski BE. Onychomycosis: pathogenesis, diagnosis, and man- agement. Clin Microbiol Rev. 1998;11(3):415-29. DOI: 10.1128/ CMR.11.3.415. PMID: 9665975. 13. Piraccini BM, Alessandrini A. Onychomycosis: A Review. J Fungi (Basel). 2015;1(1):30-43. DOI: 10.3390/jof1010030. PMID: 29376897. 14. Tosti A, Baran R, Piraccini BM, Fanti PA. “Endonyx” onychomyco- sis: a new modality of nail invasion by dermatophytes. Acta Derm Venereol. 1999;79(1):52-3. DOI: 10.1080/000155599750011714. PMID: 10086860. 15. Lipner SR, Scher RK. Onychomycosis: Clinical overview and di- agnosis. 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