Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2024;14(1):e2024017 1 A Rare Case of Follicular Porokeratosis Ptychotropica: When Dermoscopy Enghlitens Clinics Nour El Imene Ouni1, Sana Mokni1, Nadia Ghariani Fetoui1, Jacem Rouatbi1, Marouen Ben kahla1, Maha Lahouel1, Amina Aounallah1 Najet Ghariani1, Badreddine Sriha2, Colandane Belajouza1, Mohamed Denguezli1 1 Dermatology department, Faculty of Medicine of Sousse, University of Sousse, Farhat Hached Hospital, Sousse, Tunisia 2 Anatomopathology Department, Faculty of Medicine of Sousse, University of Sousse, Farhat Hached Hospital, Sousse, Tunisia Key words: Porokeratosis ptychotropica, follicular involvement, dermoscopy, histopathology Citation: Ouni NI, Mokni S, Ghariani Fetoui N, et al. A Rare Case of Follicular Porokeratosis Ptychotropica: When Dermoscopy Enghlitens Clinics. Dermatol Pract Concept. 2024;14(1):e2024017. DOI: https://doi.org/10.5826/dpc.1401a17 Accepted: June 23, 2023; Published: January 2024 Copyright: ©2024 Ouni 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: Dr Ouni Nour el Imene, M.D, Farhat Hached Hospital, University of Medicine, Sousse, Tunisia. Tel: +21624041144 Email: nourelimene286@gmail.com Introduction Porokeratosis is an epidermal keratinization disorder characterized clinically by annular plaques with keratotic ridge and an atrophic center. Several variants have been described  [1]. Porokeratosis ptychotropica (PP) has been recently individualized as a new variant [2]. It is charac- terized by verrucous plaques localized in the regions of the buttocks, most commonly the gluteal cleft. Its dermoscopic features have been rarely reported [2]. Herein, we describe a rare case of PP with follicular involvement and particular dermoscopic patterns. Case Presentation A 48-year-old man with no particular medical history pre- sented to our outpatient department with the chief com- plaint of pruritic gluteal lesions evolving for 15 years. Family history revealed no similar lesions. Physical examination noted well-demarcated, red–brown and verrucous plaques located on both buttocks with satellite hyperkeratotic, pap- ules (Figure 1A). Dermoscopy showed a raised scaly rim, limiting a non-atrophic center, gray-brown dots, and pig- mentation along the keratin rim (Figure 1B). Interestingly, we noted prominent follicular plugging and follicular spic- ules in 2 lesions (Figure 1, C and D). Multiple polymorphous vessels are present within the keratin rim as well as periph- eral vascularization adjacent to but outside the keratin rim (Figure 1, C and D). A skin biopsy specimen showed epi- dermal hyperplasia, multiple cornoid lamellae in the stratum corneum with an absence of underlying granular zone, and dyskeratotic cells in the spinous layer. Slight lymphocytic in- filtration was also seen in the upper dermis. Multiple serial sections revealed cornoid lamella involving the follicular in- fundibulum (Figure 2). Based on clinical, dermoscopic, and histopathological features, the diagnosis of PP with follicular 2 Research Letter | Dermatol Pract Concept. 2024;14(1):e2024017 involvement was established. The patient was treated with CO2 laser vaporization for the verrucous lesions. We ob- tained the patient’s consent. Conclusions PP is a rare form of porokeratosis. Since its first description by Lucker et al in 1995, about 30 cases have been reported in the literature. Misdiagnosis of PP is common, and differ- ential diagnosis often includes psoriasis, chronic eczema, Bowen disease, dermatophytosis and candidiasis [2]. Histo- pathology generally confirms the diagnosis showing multiple cornoid lamellae [2]. Dermoscopy is of recognized value in assisting the diagnosis of porokeratosis. However, only a few cases describe the dermoscopic features of PP [2,3]. The most common dermoscopic patterns, which are not specific to this variant include a characteristic keratin rim and dotted vessels [2,3]. The peripheral vascularization observed in our case have been rarely reported in porokeratosis [3]. More- over the keratotic follicular plugs which were present in our patient have been recently described in only 3 cases: 2 in the face and one in the scalp [4,5]. It reflects the follicular in- volvement in porokeratosis. In fact, follicular porokeratosis is a newly described variant with less than 20 reported cases, Figure 1. (A-D) A 48-year-old man with no particular medical history who presented with: (A) Ptychotropic porokeratosis showing well-de- marcated, red–brown, and verrucous plaques located on both buttocks with satellite roundish, hyperkeratotic, brownish papule. (B) Polarized dermoscopic image (10X Dermlite DL4) showing a raised scaly rim (black arrow), limiting a non-atrophic center with gray-brown dots and pigmentation along the keratin rim (red arrow). (C,D) Polarized dermoscopic image (10X Dermlite DL4) showing a cobblestone-like pattern with prominent keratotic follicular plugs (black arrow) and spicules (blue arrow). Multiple polymorphous peripheral vessels are present within the keratin rim (red arrow). Research Letter | Dermatol Pract Concept. 2024;14(1):e2024017 3 in which dyskeratosis extending into the follicular infundib- ulum is the hallmark of histopathology. It classically pres- ents, in middle-aged patients with porokeratosis of Mibelli and disseminated superficial actinic porokeratosis [6]. In conclusion, we reported a rare case of follicular PP and highlighted the role of dermoscopy in guiding the di- agnosis of such atypical clinical presentation with the recently-described dermoscopic pattern of follicular plug- ging and spicules as a diagnostic key for the follicular involvement. We aimed by presenting this case to gain up-to- date knowledge on this rare entity. References 1. Das A, Vasudevan B, Talwar A. Porokeratosis: An enigma begin- ning to unravel. Indian J Dermatol Venereol Leprol. 2022;88(3): 291-299. DOI: 10.25259/IJDVL_806_20. PMID: 34877845. 2. Lacarrubba F, Musumeci ML, Verzì AE, Poma C, Caltabiano R, Micali G. Porokeratosis Ptychotropica: Dermoscopy, Reflec- tance Confocal Microscopy, and Histopathological Correla- tion. Indian J Dermatol. 2021;66(5):540-542.  DOI: 10.4103/ijd .ijd_894_20. PMID: 35068510. PMCID: PMC8751715. 3. Zaar O, Polesie S, Navarrete-Dechent C, et al. Dermoscopy of porokeratosis: results from a multicentre study of the Interna- tional Dermoscopy Society.  J Eur Acad Dermatol Venereol. 2021;35(10):2091-2096. DOI: 10.1111/jdv.17439. PMID: 34077570. 4. Bhatia S, Pai S, Shenoi S, Prabhu S, P SS, Goyal S. Follicular plugging: A new dermoscopic feature in porokeratosis. J Pak Assoc Dermatol [Internet]. 2021;30(4):674-676. Available from: https://www.jpad.com.pk/index.php/jpad/article/view/1521 Ac- cessed [ 01/05/2023 ]. 5. Gómez-Zubiaur A, Medina-Expósito I, Fernández-Flores A, Trasobares-Marugán L. Follicular Porokeratosis of the Scalp: First Description of Clinical and Trichoscopic Features. Int  J Trichology. 2022;14(1):25-27. DOI: 10.4103/ijt.ijt_86_20. PMID: 35300103. PMCID: PMC8923138. 6. Zhao M, Sanusi T, Zhao Y, Huang C, Chen S. Porokeratosis with follicular involvement: report of three cases and review of literatures. Int J Clin Exp Pathol. 2015;8(4):4248-4252. PMID: 26097620. PMCID: PMC4467007. Figure 2. The epidermis shows hyperplasia, multiple cornoid lamel- lae in the stratum corneum with cornoid lamella involving the fol- licular infundibulum, an absence of underlying granular zone and dyskeratotic cells in the spinous layer. The superficial dermis con- tains slight lymphocytic infiltration (H&E stain X40).