Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2023;13(3):e2023242 1 Ultraviolet-Induced Fluorescence Dermatoscopy Reveals Fluorescent Clues in Pitted Keratolysis Paweł Pietkiewicz1,2, Cristian Navarrete-Dechent3,4, Natalia Salwowska2,5, Carmen Cantisani6, Mohamad Goldust7, Enzo Errichetti8 1 Dermatology Private Practice, Poznań, Poland 2 Polish Dermatoscopy Group, Poznań, Poland 3 Department of Dermatology, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 4 Melanoma and Skin Cancer Unit, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 5 Department of Dermatology, School of Medicine, Medical University of Silesia, Katowice, Poland 6 Dermatology Unit, Department of Clinical Internal Anesthesiologic Cardiovascular Sciences, “Sapienza Medical School” University of Rome, Rome, Italy 7 Department of Dermatology, Yale School of Medicine, Yale University, New Haven, Connecticut, USA 8 Institute of Dermatology, Santa Maria della Misericordia University Hospital, Udine, Italy Key words: ultraviolet radiation, dermoscopy, pitted keratolysis, corynebacterium, fluorescence Citation: Pietkiewicz P, Navarrete-Dechent C, Salwowska N, Cantisani C, Goldust M, Errichetti E. Ultraviolet-Induced Fluorescence Dermatoscopy Reveals Fluorescent Clues in Pitted Keratolysis. Dermatol Pract Concept. 2023;13(3):e2023242. DOI: https://doi.org/10.5826/dpc.1303a242 Accepted: April 12, 2023; Published: July 2023 Copyright: ©2023 Pietkiewicz 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: Paweł Pietkiewicz, Centrum Medyczne Zwierzyniecka, Zwierzyniecka Street 30/28, Poznań 60-814. Telephone: +48 602 133 503 E-mail: pietkiewicz.pp@gmail.com Introduction Pitted keratolysis (PK) is a corynebacterial infection of the soles manifesting as multiple plantar pits caused by desmo- somal alteration in the stratum corneum due to enzymatic activity of P1 and P2 bacterial serine proteases [1]. Predis- posing factors include hyperhidrosis, occlusion, and reduced acidity of the skin surface [1]. Apart from the pits, patients may report burning sensa- tion and malodour. In some instances, PK may be accompa- nied with other corynebacterial infections such as erythrasma and/or trichobacteriosis axillaris [2]. Although the diagnosis is mostly based on clinical presentation, differentiation from clinically similar conditions, mainly including viral warts and tinea pedis, may sometimes be troublesome. In such cases, recognition of PK may be assisted by dermatoscopy (multiple crateriform indentations of the soles), Wood lamp examination (coral red fluorescence of the pits), direct mi- croscopy, and culture. Case Presentation A 49-year-old male presented to the dermatology outpatient clinic due to genital lichen sclerosus. During the skin check, multiple plantar and interdigital pits were noted and further confirmed with dermatoscopy (Figure 1). Ultraviolet-induced 2 Research Letter | Dermatol Pract Concept. 2023;13(3):e2023242 Figure 1. Pitted keratolysis in a 49-year-old patient. (A) Clinical presentation showing crateriform plantar pits (black arrowheads). (B)  Examination with Wood lamp displays coral-red excited fluorescence of the pits (black arrowheads) and polycyclic figures (white arrowheads). (C) Dermatoscopy of toe web space displays small pits with a free edge of the peripheral scale that coalesce into larger areas (black arrowheads). (D) Ultraviolet-induced fluorescence dermatoscopy of toe web space reveals excited fluorescence - coral-red eccrine dots (white frames; magnified view in the box) and perieccrine clods (black arrowheads) corresponding to crateriform pits. (E) Dermatoscopy of the sole shows sparse plantar pits with a free edge of peripheral scale (black arrowheads) and irregular scaling, seen mainly in the furrows (white arrowheads). (F) Ultraviolet-induced fluorescence dermatoscopy of the sole reveals excited fluorescence - pale coral-red pits with a free edge of scale (black arrowheads) and pale coral-red parallel ridge pattern, as well as pale coral-red clods in the ridges (white arrows) (DL5, Dermlite,×10 magnification). Research Letter | Dermatol Pract Concept. 2023;13(3):e2023242 3 fluorescence dermatoscopy (UVFD; peak wavelength 365nm, DL5, Dermlite) displayed multiple pits surrounded with coral-red scale, coral-red parallel ridge pattern (PRP) (absent in visible light), and coral-red eccrine dots and clods. Conclusions UVFD is a novel diagnostic technique implementing UV radiation to produce fluorescent images based on Stokes shift phenomenon [3,4]. Coral-red excited emission spec- trum is likely caused by the presence of Corynebacteria producing coproporphyrin III [5]. We hypothesize that the infection might begin within the acrosyringium as a coral-red eccrine dots and clods that precede the develop- ment of coral-red PRP and finally develop into coral-red crateriform pits. The presence of the PRP pattern in mis- cellaneous dermatoses was summarized in Table   1. The specificity of our findings requires further confirmation in larger series of cases. In our opinion, these newly re- ported UVFD clues might be helpful to promptly differen- tiate PK from its common clinical and/or dermatoscopic mimickers. Table 1. Differential diagnosis of parallel ridge pattern on dermatoscopy. Diagnosis Clues Clinical Pearl Acral lentiginous melanoma Usually other clues to melanoma; chaotic distribution of structures, colours (patchy pigmentation) or border abruptness; accentuated perieccrine pigmented circles, obliterated eccrine duct openings; solitary standing-out lesion (‘a priest in the snow’); large size (>7mm) Acral compound or combined nevus Usually long history or congenital character; concentric architecture and/or elevation Exogenous pigmentation (e.g. dirt, hair dye, henna, silver nitrite, potassium permanganate, etc.) Different shades depending on pigment colour In many instances can be removed with alcohol pad Ethnic pigmentation No other melanoma features; harmonious in regard to structure and colour distribution; multiple Laugier-Hunziker syndrome / Peutz-Jeghers syndrome No other melanoma features; harmonious in regard to structure and colour distribution; multiple; possibly accompanied by longitudinal melanonychia and/or mucosal melanotic macules Acral angioma Presence of red dots on the ridge; organized Subcorneal hemorrhage Often well-defined, ‘cracked’ appearance, orange, reddish- to-black colour Can be removed with scalpel Acral pigmented viral wart Patchy pigmentation resembling acral lentiginous melanoma, yet no other melanoma features Pitted keratolysis Multiple crateriform pits with a free edge of scale; common history of plantar hyperhidrosis Parallel ridge pattern can be visualized with ultraviolet- induced fluorescence dermatoscopy only Tinea nigra Short history: brown to gray pigmentation arranged in thin bundles of short lines (‘spicules’) forming reticulate pattern, but also parallel ridge pattern especially at the lesion’s periphery; no parallel furrow pattern References 1. 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