Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2024;14(4):e2024248 1 Scalp Porokeratosis: Dermoscopy Key Role in Unmasking a Hidden Condition Rosario Agüero1, Cristián Navarrete-Dechent1,2, Bengu Nisa Akay3 1 Department of Dermatology, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 2 Melanoma and Skin Cancer Unit, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3 Ankara University, Medicine Faculty, Department of Dermatology, Ankara, Turkey Key words: Porokeratosis, Dermoscopy, Actinic keratosis Citation: Agüero R, Navarrete-Dechent C, Akay BN. Scalp Porokeratosis: Dermoscopy Key Role in Unmasking a Hidden Condition. Dermatol Pract Concept. 2024;14(4):e2024248. DOI: https://doi.org/10.5826/dpc.1404a248 Accepted: June 1, 2024; Published: October 2024 Copyright: ©2024 Agüero 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: Bengu Nisa Akay, MD, Ankara University, Medicine Faculty Department of Dermatology, Phone: 0090532 3047292 Address Fatih Sultan Mah, Baskent Loft Evleri, 412/42, Etimesgut, Ankara, Turkey. Email: nisaakay@gmail.com Introduction Porokeratosis encompasses a spectrum of disorders affecting epidermal keratinization characterized by the presence of a cornoid lamella on histopathology [1]. While porokeratosis can manifest in various locations, lesions are typically found on the trunk and extremities. However, rare instances of porokeratosis arising on the sun-damaged scalp of elderly patients have been documented. This anatomical location, a common site for actinic keratosis (AK) occurrence, poses diagnostic challenges due to overlapping clinical and dermo- scopic features between the two conditions [2,3]. Despite this, porokeratosis is often overlooked in the differential diagnosis of scalp lesions. Herein we present four cases of scalp porokeratosis, highlighting their clinical, histopatho- logical, and dermoscopic features. Case Presentation Four histopathologically confirmed cases of scalp porokera- tosis in elderly males, aged 60 to 84, with skin types 3 and 4 are presented. The lesions were localized in areas devoid of hair due to androgenetic alopecia (AGA). Clinically, the lesions manifested as erythematous rough scaly plaques on sun-damaged areas with multiple lentigines. Dermoscopic examination revealed consistent features across all lesions, including an annular double-edged hyperkeratotic scale, with vascular structures observed in three patients, shiny white structures in three, and follicular plugs in three. One patient presented with multiple scalp lesions, while the re- maining three had solitary lesions. There were no lesions elsewhere on the body besides the scalp in the four patients. On histopathology, all cases presented with cornoid lamella 2 Research Letter | Dermatol Pract Concept. 2024;14(4):e2024248 characterized by columns of hyperkeratosis and parakerato- sis. Loss of granular layer and dyskeratosis in the epidermis under the cornoid lamella was also present. Detailed charac- teristics of the patients are summarized in Table 1. Clinical, dermatoscopic, and histopathologic photos are presented in Figures 1-2. Patients were treated with cryotherapy with complete response. Conclusion Our small cohort highlights four cases of porokeratosis af- fecting only the scalp of older men with androgenetic alopecia (AGA), a typical area for actinic keratosis (AK). The over- lapping risk factor of chronic UV exposure underscores the importance of distinguishing between these conditions, yet porokeratosis remains under-recognized in this anatomical location. Dermoscopy emerges as a valuable tool for diagnos- ing scalp porokeratosis as it exhibits consistent features with those observed elsewhere on the body, particularly the char- acteristic double-edged hyperkeratotic rim of scale. More- over, additional diagnostic modalities such as ink-enhanced dermoscopy [4], ultraviolet-induced fluorescence dermoscopy (UVFD), and reflectance confocal microscopy [5] may aid in differentiation from AK, the primary differential diagnosis. Table 1. Clinical Characteristics of the Patients. Case# Age Sex AGA Dermatoscopic Features Single vs multiple Treatment Keratin rim (hyperpigmented) Vascular structures Shiny white structures Follicular plugs 1 72 M Yes Yes Yes Yes Yes Single Cryotherapy 2 76 M Yes Yes No Yes Yes Single Cryotherapy 3 84 M Yes Yes Yes Yes Yes Single Cryotherapy 4 60 M Yes Yes Yes No Yes Multiple Cryotherapy Thomsen et al.* 83 M Yes -- -- -- -- Single -- Gomez-Zubiaur et al.** 82 M Yes No Yes No Yes Multiple N/A Naineni et al.*** 66 M Yes -- -- -- -- Multiple No active treatment Sidwell et al.+ 70 M Yes -- -- -- -- Multiple Cryotherapy Nenoff et al.++ 62 M Yes -- -- -- -- Multiple Topical urea + tretinoin Abbreviations: AGA: androgenetic alopecia; M: male; N/A not available or not described. * J Cutan Pathol 1979 Apr;6(2):134-38; ** Int J Trichology 2022 Jan-Feb;14(1):25-27. *** Clin Exp Dermatol 2007 Mar;32(2):222-3. + Br J Dermatol 2003 Sep;149(3):654. ++ Hautarzt 2011 Jul;62(7):544-7. Figure 1. (A) Clinical, (B) dermoscopic, and (C, D) histopathological images of patient number 1. H&E staining highlights the cornoid lamella characterized by alternating columns of hyperkeratosis and parakeratosis (yellow arrows) in the epidermis, with underlying orthokeratosis. There is a loss of the granular layer and evidence of dyskeratosis in the epidermis beneath the cornoid lamella (yellow circle). Research Letter | Dermatol Pract Concept. 2024;14(4):e2024248 3 In conclusion, porokeratosis should be considered a potential differential diagnosis for scalp lesions, necessitat- ing accurate diagnosis for appropriate management. With advancements in targeted therapy, novel treatments like top- ical cholesterol/lovastatin offer promising options for poro- keratosis, emphasizing the significance of its recognition in dermatologic practice [6]. References 1. Sertznig P, von Felbert V, Megahed M. Porokeratosis: present concepts. J Eur Acad Dermatol Venereol. 2012;26(4):404-412. doi:10.1111/j.1468-3083.2011.04275.x 2. 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 3. Sidwell RU, Seet JE, Francis N, Bunker CB. Giant actinic po- rokeratosis of the scalp.  Br J Dermatol. 2003;149(3):654. doi:10.1046/j.1365-2133.2003.05485.x 4. Navarrete-Dechent C, Uribe P, Marghoob A. Ink-enhanced der- moscopy is a useful tool to differentiate acquired solitary plaque porokeratosis from other scaly lesions.  J Am Acad Dermatol. 2019;80(6):e137-e138. doi:10.1016/j.jaad.2017.11.052 5. Ulrich M, Forschner T, Röwert-Huber J, et al. Differentiation be- tween actinic keratoses and disseminated superficial actinic poro- keratoses with reflectance confocal microscopy. Br J Dermatol. 2007;156 Suppl 3:47-52. doi:10.1111/j.1365-2133.2007.07862.x 6. Atzmony L, Lim YH, Hamilton C, et al. Topical cholesterol/ lovastatin for the treatment of porokeratosis: A pathogenesis- directed therapy.  J Am Acad Dermatol. 2020;82(1):123-131. doi:10.1016/j.jaad.2019.08.043 Figure 2. Clinical and dermoscopic photos of patients (A, B) 1, (C, D) 2, and (E, F) 3. Der- moscopic photos show keratin rim (red arrows), follicular plugs (yellow arrows), vascular structures (white circles), and shiny white structures (black circles).