Dermatology: Practical and Conceptual Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 1 Benign Keratosis: A Useful Term? Rebecca Scott1, Amanda Oakley2,3 1 University of Aberdeen, Waikato Hospital, Hamilton, New Zealand 2 Waikato District Health Board, Hamilton, New Zealand 3 University of Auckland, Faculty of Medical and Health Science Medical School, Waikato Campus, Auckland, New Zealand Key words: benign keratosis, seborrhoeic keratosis, lichen planus-like keratosis, solar lentigo, dermoscopy Citation: Scott R, Oakley A. Benign Keratosis: A Useful Term? Dermatol Pract Concept. 2023;13(2):e2023115. DOI: https://doi .org/10.5826/dpc.1302a115 Accepted: November 9, 2022; Published: April 2023 Copyright: ©2023 Scott 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: Amanda Oakley, Waikato District Health Board, Pembroke Street, 183 Pembroke Street, Hamilton, New Zealand 3204. University of Auckland, Faculty of Medical and Health Science Medical School, Waikato Campus. Email: amanda.oakley@waikatodhb.health.nz; Amanda.oakley@me.com Introduction: Seborrheic keratosis (SK), lichen planus-like keratosis (LPLK), and solar lentigo (SL) are common benign skin lesions. These lesions are frequently seen adjacent to each other or can arise from one another. They can sometimes be difficult to differentiate despite having distinct histopathological features. Objectives: We evaluated dermoscopic images of 80 skin lesions to confirm the term ‘benign kerato- sis’ is useful for an undifferentiated SK/LPLK/SL where there are overlapping clinical and dermoscopic characteristics. Methods: Clinical and dermoscopic images were sourced from a teledermoscopy service database of 13,000 lesions in 7,000 patients. The database was queried for SK, SL or LPLK in sun-exposed sites. Each lesion was evaluated based on specific dermoscopic criteria and the results analyzed. Results: Lesions were identified with mixed clinical and dermoscopic criteria of SK and SL, and in some, dermoscopic criteria for LPLK were also present. Conclusions: This study highlights the relationship between these lesions. We confirm the term ‘benign keratosis’ is useful for mixed lesions or for those that are difficult to classify. ABSTRACT Introduction Seborrheic keratosis (SK), solar lentigo (SL) and lichen planus-like keratosis (LPLK, also known as lichenoid keratosis), can be difficult to differentiate although each has defined clinical and dermoscopic characteristics [1]. The his- topathological features of SK, LPLK and SL differ but as they are benign, only those suspicious of melanoma are subjected 2 Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 to biopsy. An SK can arise from an SL and an LPLK can arise from an SL or from an SK. There is limited research linking these three lesions [2]. The International Skin Imaging collaboration (ISIC) aims to improve early melanoma detection [3]. ISIC has hosted challenges since 2016 covering lesion segmentation, detec- tion of clinical diagnostic patterns, and lesion classification with the purpose of developing computer-based image anal- ysis tools. The 2019 ISIC challenge classified pigmented le- sions into 9 diagnostic categories including ‘benign keratosis’ (seborrheic keratosis, solar lentigo, and lichen planus-like keratosis) [4]. The ISIC public-access archive includes more than one thousand dermoscopic images classified as ‘benign pigmented keratosis’ [5]. However, the term ‘benign keratosis’ is not well known by dermatologists. The classification of these entities by clin- ical terminology tools is inconsistent. • ICD-11 (version 09/2020) lists all three entities within the benign squamous cell neoplasm category (seborrheic ker- atosis XH0949, solar lentigo XHB58, lichen planus-like keratosis XH63L8), and includes a separate entry for be- nign keratosis, NOS (XH0S03). • ICD-11 also lists seborrheic keratosis and lichen planus-like keratosis within benign keratinocytic acan- thoma (2F21) and solar lentigo within photoaging of the skin (EJ20) [6]. • The SNOMED International SNOMED CT browser (31 January 2021 edition) does not link seborrheic keratosis (disorder code SCTID: 394726009) and solar lentigo (disor- der code SCTID: 72100002), and lichenoid keratosis is clas- sified as lichenoid actinic keratosis (SCTID: 403198004) [7]. SK is a common benign epidermal age-related prolifer- ation of keratinocytes [8]. SK can occur anywhere on the body sparing the mucous membranes, palms and soles. There are several histological subtypes which often overlap; they are characterized by acanthosis, papillomatosis, hyperkera- tosis and the presence of pseudocysts [9]. SL is a macular hyperpigmented lesion linked to chronic sun exposure. Typical histological features are acanthosis with elongated epidermal ridges with accompanying actinic elastosis [10]. LPLK, also known as lichenoid keratosis, is thought to represent an inflammatory regressive response to a pre-existing cutaneous lesion. The pathogenesis is not com- pletely understood, however most literature suggests LPLK is a regressive form of benign epithelial neoplasm such as an SK or SL [11-13]. LPLK lesions can be seen in multiple regressive stages and therefore can often be confused with other skin tumors including basal cell carcinoma and mela- noma [14]. Histological features are lichenoid lymphocytic infiltrate, hyperkeratosis with focal parakeratosis, variable hypergranulosis and focal acanthosis. Eosinophils and plasma cells with Civatte bodies are also noted [15]. A link between SL and SK was supported by histolog- ical evidence of transformation in 50 cases, and histolog- ical SL was documented at the periphery of 50 specimens of LPLK [16]. Biopsies taken from a solitary lesion 5 years apart reported the evolution of a SL into a solitary LPLK [17]. In a series of 100 cases of LPLK evaluated by histol- ogy, 28% had an adjacent skin lesion, most commonly SK (8.4%), SL (7%) and actinic keratosis (5.6%) [18]. A fur- ther clinicopathologic review of LPLK cases confirmed the most frequently seen adjacent lesions were SL (73%) and SK (6.5%) [2]. Gene mutations (FGFR3 and PIK3CA) have been identified in SL and SK to support a link between them [14]. Objectives The main objective of the study was to confirm the term ‘benign keratosis’ is useful, by comparing the clinical and dermoscopic features of typical SK,SL, LPLK and lesions in which overlapping features were present. Methods Clinical and dermoscopic images were sourced from a teleder- moscopy service database of 13,000 lesions in 7,000 patients [19]. The database was queried for SK, SL or LPLK in sun- exposed sites (scalp, ears, face) (Table 1). Non-randomized lesions were selected that had good quality clinical images typical for SK (N=20), SL (N=20), LPLK (N=20) or having mixed clinical features (N=20), ie SK+SL+/-LPLK), matched for anatomical area and camera (3Gen DermLiteCam V1). Lesions identified as clinically ‘benign’ were not formally excised, therefore histopathological findings were not avail- able. Each lesion was evaluated using specific dermoscopic criteria for SK, SL, and LPLK (1) (Table 2). Results The 80 lesions evaluated were associated with 440 mac- roscopic, polarized and nonpolarized dermoscopic images (Table 3). Dermoscopic Criteria of Seborrheic Keratosis (Table 4) Analysis of SKs revealed that: • SKs exhibited an average of 3.3 SK criteria. • Three or more of the five SK criteria were present in 17/20 SKs. • ‘Sharply demarcated border’ and ‘lines curved and thick (cerebriform)’ were each present in 19/20 SKs. Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 3 Table 2. Dermoscopic criteria for seborrheic keratosis, solar lentigo, and lichen planus-like keratosis. Seborrheic Keratosis Solar Lentigo Lichen planus-like Keratosis • Sharply demarcated border • Dots or clods white clustered or disseminated • Clods brown-yellow or orange (rarely black) • Lines curved and thick • Lines brown curved parallel thin • Sharply demarcated • Scalloped border • Homogenous brown pigmentation • Homogenous and structureless pigmentation • Faint reticulation • Fine parallel lines • Fine parallel lines • Ink spot lentigo excluded • Fine scale • Polymorphous vessels • Dotted vessels • Gray dots • Diffuse gray dotted pattern • Color (white, pink, red, orange, purple, blue-gray, black, light brown, dark brown) • Color red excluded Table 3. Average number of dermoscopic criteria present in SK/SL/LPLK lesion group. Lesion type SK Criteria SL Criteria LPLK Criteria SK 3.3/5 (66%) 1.8/6 (31%) 0.0/5 (0%) SL 2.0/5 (40%) 5.3/6 (88%) 1.0/5 (2%) LPLK 0.6/5 (12%) 2.4/6 (34%) 1.8/5 (35%) Mixed 3.75/5 (75%) 4.4/6 (73%) 0.6/5 (12%) LPLK = Lichen-planus like keratosis; SK = Seborrheic keratosis; SL = Solar lentigo. Table 1. Original database collection with patient demographics. • ‘Clods brown-yellow or orange (rarely black)’ were pres- ent in 16/20 SKs. • ‘Dots or clods white clustered or disseminated’ and ‘lines brown curved parallel thin’ were present in 6/20 SKs. SK criteria were less common in SLs with the exception of ‘Sharply demarcated border’ seen in 18/20, a shared char- acteristic of SL lesions. ‘Lines curved and thick (cerebriform)’ and ‘Lines brown curved parallel thin’ were seen in 8/20 and 10/20 SL lesions consecutively. 4 Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 SL criteria were less common in the SK group except for ‘sharply demarcated border’, which was present in 19/20 SL lesions. ‘Faint reticulation’ and ‘scalloped border’ were seen in 4/20 and 7/20 SK lesions consecutively. Certain SL criteria were high in LPLK lesions. ‘Struc- tureless (amalgamate of homogenous and structureless pig- mentation)’ was present in in 18/20 and ‘scalloped border’ in 14/20 LPLK lesions. ‘Homogenous brown pigmentation’ and ‘fine lines parallel’ were present in none of the LPLKs. All mixed lesions had three or more SL criteria. None had ‘homogenous brown pigmentation’. ‘Scalloped border’ was present in 19/20 and ‘structureless’ in 17/20 of mixed lesions. • The mixed lesion group had an average of 73% SL criteria. • The SL and LPLK groups had an average of 88% and 34% SL criteria respectively. Dermoscopic Criteria of Lichen Planus-Like Keratosis (Table 6) • LPLKs exhibited an average of 1.75 LPLK criteria: • ‘Diffuse gray dotted pattern’ was present in all 20 LPLK lesions. • ‘Gray dots’ were present in 10/20 LPLK lesions. • There were no ‘polymorphous vessels’ in LPLK lesions and ‘fine scale’ was present in only 1/20 LPLK lesions. No LPLK criteria were present in SK lesions. SL findings were less common also with 3 out of the 5 criteria having SK features were present to a lesser degree in LPLK lesions. A ‘Sharply demarcated border’ was present in 6/20 LPLKs, ‘Lines curved and thick (cerebriform)’ in 4/20 and ‘Clods brown-yellow or orange (rarely black) were present in 2/20. No LPLKs had ‘dots or clods white clustered or dis- seminated’ or ‘lines brown curved parallel thin’. All 5 SK criteria were present in 6/20 of the mixed le- sions; 19/20 had a ‘sharply demarcated border’ and ‘dots or clods white clustered or disseminated’, ‘clods brown-yellow or orange (rarely black)’ and ‘lines brown curved parallel thin’ were commonly seen. • The mixed lesion group had an average of 75% SK criteria. • The SL and LPLK groups had an average of 40% and 12% SK criteria respectively. Dermoscopic Criteria of Solar Lentigo (Table 5) Analysis of SLs revealed that: • SLs exhibited an average of 5.28 SL criteria. • Four or more of the SL criteria were present in 19/20 SL lesions. • ‘Faint reticulation’ and ‘scalloped border’ were each pres- ent in all 20 SL lesions. • ‘Homogenous brown pigmentation’ was present in 17/20 SL lesions. • ‘Structureless (amalgamate homogenous and structureless pigmentation)’ was present in 16/20 lesions and ‘fine lines parallel’ was present in 14/20 lesions. Table 4. Dermoscopic criteria for seborrheic keratosis in various clinically diagnosed lesions. Lesion Type Sharply demarcated border Dots or clods white clustered or disseminated Clods brown, yellow or orange (rarely black) Lines curved and thick (cerebriform) Lines brown curved parallel thin SK 19/20 (95%) 6/20 (30%) 16/20 (80%) 19/20 (95%) 6/20 (30%) SL 18/20 (90%) 2/20 (10%) 2/20 (10%) 8/20 (40%) 10/20 (50%) LPLK 6/20 (30%) 0/20 (0%) 2/20 (10%) 4/20 (20%) 0/20 (0%) Mixed 19/20 (95%) 11/20 (55%) 17/20 (85%) 16/20 (80%) 12/20 (60%) LPLK = Lichen-planus like keratosis; SK = Seborrheic keratosis; SL = Solar lentigo. Table 5. Dermoscopic criteria for solar lentigo in various clinically diagnosed lesions. Lesion Type Sharply demarcated border Homogenous brown pigmentation Structureless (~10%) Faint reticulation (criss-cross network) Scalloped border Fine lines parallels SK 19/20 (95%) 2/20 (10%) 0/20 (0%) 4/20 (20%) 7/20 (35%) 4/20 (20%) SL 18/20 (90%) 17/20 (85%) 16/20 (80%) 20/20 (100%) 20/20 (100%) 13/20 (65%) LPLK 6/20 (30%) 0/20 (0%) 18/20 (90%) 9/20 (45%) 14/20 (70%) 0/20 (0%) Mixed 19/20 (95%) 0/20 (0%) 17/20 (85%) 16/20 (80%) 19/20 (95%) 15/20 (75%) LPLK = Lichen-planus like keratosis; SK = Seborrheic keratosis; SL = Solar lentigo. Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 5 Table 6. Dermoscopic criteria for lichen planus-like keratosis in various clinically diagnosed lesions. Lesion Type Fine scale Polymorphous vessels Dotted vessels (small red dots) Gray dots Diffuse gray dotted pattern SK 0/20 (0%) 0/20 (0%) 0/20 (0%) 0/20 (0%) 0/20 (0%) SL 0/20 (0%) 0/20 (0%) 0/20 (0%) 1/20 (5%) 1/20 (5%) LPLK 1/20 (5%) 2/20 (10%) 2/20 (10%) 10/20 (50%) 20/20 (100%) Mixed 3/20 (15%) 0/20 (0%) 0/20 (0%) 4/20 (20%) 4/20 (20%) LPLK = Lichen-planus like keratosis; SK = Seborrheic keratosis; SL = Solar lentigo. Figure 1. Mixed Lesion displaying appearance of SK arising from SL. Lesion ID 15040477. Dermoscopy features —sharply demarcated border, dots or clods white clustered or disseminated, clods brown yellow or orange (rarely black), Lines curved and thick (cerebriform), lines brown curved parallel thin, faint reticulation (criss-cross network), scalloped border, fine lines parallels. Figure 2. Seborrhoeic Keratosis classical lesion. Lesion ID 35110201. Dermoscopy features — sharply demarcated border, dots or clods white clustered or disseminated, clods brown-yellow or orange (rarely black), lines curved and thick (cerebriform), lines brown curved parallel thin. Figure 3. Solar Lentigo classical lesion. Lesion ID 44740194. Dermoscopy features — sharply demarcated border, homogenous brown pig- mentation, structureless (approx. 10%), faint reticulation (criss-cross network), scalloped border, fine lines parallel. 6 Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 lowest positive result for SK criteria had a thick scale reduc- ing dermoscopic feature detail. The SL criterion ‘scalloped border’ was present in all 20 SL and Mixed lesions. ‘Faint reticulation’ was seen in 16/20 Mixed lesions. LPLK lesions also displayed SL features. A high percentage of classic LPLK lesions displayed specific SL criteria including ‘Structureless’ (18/20), ‘Scalloped border’ (14/20) and ‘faint reticulation (criss-cross network)’ (9/20). LPLK may arise from an SL with sections of the lesion rep- resenting regressive structures of SL. ‘Faint reticulation’ and ‘scalloped border’ were seen in all 20 SL lesions confirming that these criteria have high specificity to SL. ‘Homogenous brown pigmentation’ showed high specificity in SL lesions and was uncommonly observed in other lesion groups. This is a classical feature of an SL; the mixed lesions had a com- bination of features and therefore could not be classified as ‘homogenous’. The key dermoscopic features in the LPLK Lesions were ‘diffuse gray dotted pattern ‘in all 20 classic LPLK lesions and ‘gray dots’ in 10/20. LPLK lesions are most easily clin- ically recognised in the late regressive stage as early phase lesions are nonspecific. Only 2/20 LPLK lesions in our selec- tive sample displayed ‘polymorphous vessels’ and ‘dot ves- sels’. ‘Fine scale’ was not displayed within any LPLK lesions however was noted in 3/20 mixed lesions. Fine scale was difficult to detect on the clinical and dermoscopic images as a contact fluid had been applied. The largest color variation group seen in LPLK was ‘light brown/grey’ in 11/20 LPLK le- sions and reflects the classic regressive features in this sample of LPLK lesions. ‘Light brown/dark brown were most com- mon in the SK, SL and Mixed groups. Few LPLK features were present in classic SL or SK lesions, however SK and SL features were displayed in LPLK lesions. SL criteria were more common with an average of 2.4/6 (34%) features pres- ent. SK features were also seen with ‘lines curved and thick (cerebriform) seen in 4/20 lesions and the common SL/SK feature of ‘sharply demarcated border’ seen in 6/20 lesions. This indicates overlap between these lesions. a 0/20 result. ‘Gray dots’ and ‘Diffuse gray dotted pattern’ were present in no SL lesions. LPLK criteria were more common in the Mixed lesions compared to classic SL and SK. ‘Diffuse gray dotted pattern’ and ‘Gray dots’ were seen in 4/20 Mixed lesions. Conclusions Analysis of the lesions selected for this study confirms that the specific dermoscopic criteria suggested in dermoscopedia for SK, SL and LPLK can be observed in the other clinically diagnosed lesions [1]. Our clinically selected SL and Mixed lesions displayed the highest number of listed dermoscopic criteria followed by SK and LPLK lesions. We found that dermoscopic criteria for clinically typical SL and SK overlap. ‘Sharply demarcated border’ was found in 19/20 (95%) of SKs and 18/20 (90%) of SLs. The SK features, ‘lines curved and thick (cerebri- form)’ and ‘lines brown curved parallel thin’ were commonly seen in SL. SL features of ‘faint reticulation’ and ‘scalloped border’ were found in otherwise typical SK. ‘Sharply demarcated border’ was present in 19/20 of the mixed group which correlates with these lesions being pre- dominantly SL or SK. The mixed lesions displayed signifi- cant findings for both SK and SL criteria, and LPLK criteria were less common. SK criteria had the highest result with an average of 3.4/5 (74%) of mixed lesions displaying SK crite- ria. Three out of five SK criteria had higher overall findings in Mixed lesions than in the SK group. SL criteria were also common with an average of 4.4/6 (73%) of Mixed lesions. Mixed lesions chosen had less LPLK criteria at 0.6/5 (12%). ‘Dots or clods white clustered or disseminated’ are typi- cal of SK but in our sample, this feature was present in 11/20 Mixed lesions and in fewer SK lesions (6/20). It may be a less common characteristic of SK or reflect the small sample size. As expected, few LPLK lesions exhibited SK criteria. A ‘sharply demarcated border’ was seen in 30% of LPLKs. We noted that 2/20 of the clinically typical SK lesions with the Figure 4. Lichen Planus-like Keratosis classical lesion. Lesion ID 46600410. Dermoscopy features — structureless (approx. 10%), faint reticulation (criss-cross network), scalloped border, grey dots, diffuse grey dotted pattern. Original Article | Dermatol Pract Concept. 2023;13(2):e2023115 7 7. SNOMED International -Medical Terminology.Available from:. https://browser.ihtsdotools.org/. Accessed July 24, 2021 8. Greco MJ, Bhutta BS. Seborrheic Keratosis. In:  StatPearls. Trea- sure Island (FL): StatPearls Publishing. Available from https:// www.ncbi.nlm.nih.gov/books/NBK545285/. Accessed August 11, 2021. 9. Hafner C, Vogt T. Seborrheic keratosis. J Dtsch Dermatol Ges. 2008;6(8):664-677. DOI:10.1111/j.1610-0387.2008.06788.x. PMID: 18801147 10. Ortonne JP, Pandya AG, Lui H, Hexsel D. Treatment of solar lentigines. J Am Acad Dermatol. 2006;54(5 Suppl 2):S262-S271. 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A clinical and histological reexamination.  Am J Surg Pathol. 1993;17(3):259-263. DOI:10.1097/00000478-199303000-00006. PMID: 8434706. 19. Lim D, Oakley AM, Rademaker M. Better, sooner, more conve- nient: a successful teledermoscopy service.  Australas J Dermatol. 2012;53(1):22-25. DOI:10.1111/j.1440-0960.2011.00836.x. PMID:  22309326. Mixed lesions displayed evidence of end-stage regressive LPLK features with the commonest features present being ‘Gray dots’ (4/20) and ‘Diffused gray dotted pattern’ (4/20). Other features were infrequent. Mixed lesions displayed a high proportion of SL/SK criteria alongside these regressive LPLK findings. This points to a relationship between the evolution of these lesions as previously documented in the literature. Benign keratoses arise in most older people. Lesions we had clinically diagnosed as SK had overlapping dermo- scopic criteria for SL, and others we diagnosed as SL had dermoscopic criteria for SK. 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