Dermatology: Practical and Conceptual Letter | Dermatol Pract Concept 2021;11(2):e2021010 1 Dermatology Practical & Conceptual New Dermoscopic Keys for Circumscribed Acral Hypokeratosis: Report of Four Cases Paula Majluf-Cáceres1, Cristián Vera-Kellet1, Sergio González-Bombardiere2 1 Department of Dermatology, Pontificia Universidad Católica de Chile 2 Department of Dermatopathology, Pontificia Universidad Católica de Chile Key words: acral hypokeratosis, image enhancement, dermatopathology, dermoscopy Citation: Majluf-Cáceres P, Vera-Kellet C, González-Bombardiere S. New dermoscopic keyes for circumscribed acral hypokeratosis: report of four cases. Dermatol Pract Concept. 2021;11(2):e2021010. DOI: https://doi.org/10.5826/dpc.1102a10 Accepted: August 9, 2020; Published: March 8, 2021 Copyright: ©2021 Majluf-Cáceres et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License BY-NC-4.0, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: None. Competing interests: The authors have no conflicts of interest to disclose. Authorship: All authors have contributed significantly to this publication. Corresponding author: Paula Majluf-Cáceres, MD, Centro Médico San Joaquin, Vicuña Mackenna 4686, Macul, Chile. Email: pamajluf@ uc.cl Introduction Descriptions of the dermoscopic features of acral hypokerato- sis (AH) are few. Clinically it can resemble other entities, such as Bowen disease or porokeratosis of Mibelli. Although AH is considered a benign pathology, in 2010 a case with actinic keratosis in the hypokeratosic epidermis and underlying elastosis was reported [1], hence the importance of knowing the dermoscopic findings for an early diagnosis and to rule out other differential or coexisting diagnoses. Case Presentation Our case series was comprised of 4 patients with AH con- firmed by biopsy in the hypothenar eminence. Figure 1A shows AH in a 61-year-old and Figure 1B a 78-year-old woman with a 10-year history of AH. Dermoscopy revealed pink areas on a red milky blush with scattered red dots, step- like scales at the periphery, and elongated whitish structures in a fibrillar raindrop pattern (Figure 1, C and D). The third case corresponded to asymptomatic AH (Figure 1E) that had developed 2 weeks after a cutting wound in a 30-year-old woman. Dermoscopy showed a red dot pattern over a homogeneous red-yellow area (Figure 1F). The fourth case was a 54-year-old woman affected by AH for 8 years (Figure 1G). Dermoscopy revealed a fine white pseudonet- work, pink stiff areas on a red milky blush with red dots, step-like scales at the periphery, and elongated whitish struc- tures in a fibrillar raindrop pattern. (Figure 1H). Microscopy revealed an area of hypokeratosis demarcated by a sharp and frayed cut-off from uninvolved acral skin with discrete hypogranulosis, dilated blood vessels in the papillary dermis, and slightly thickened collagen fibers in the reticular dermis (Figure 2). 2 Letter | Dermatol Pract Concept 2021;11(2):e2021010 Figure 1. Clinical and dermoscopic features. (A and B) Cases 1 and 2: Atrophic erythematous plaque with an irregular hyperkeratotic border. (C) Dermoscopy shows pink areas on a red milky blush with scattered red dots, step-like scales at the periphery and elongated whitish structures in a raindrop pattern. (D) Dermoscopy shows red milky blush, pink islets with dotted vessels, elongated whitish structures in raindrop pattern and staircase sign. (E) Case 3: Depressed erythematous plaque, surrounded by an hyperkeratotic border. (F) Dermoscopy showed a red dot pattern over a homogeneous red-yellow area. Letter | Dermatol Pract Concept 2021;11(2):e2021010 3 Figure 2. Histology displays an area of hypokeratosis demarcated by a sharp and frayed cut-off from uninvolved acral skin with dis- crete hypogranulosis, dilated blood vessels in the papillary dermis and slightly thickened collagen fibers in the reticular dermis (H&E, ×10). Conclusions Previous case series reported star-like desquamation at the periphery,and a well-demarcated erythema with reddish dots. These structures correlate with histopathological studies show- ing a sharply demarcated area of hypokeratosis, dilated capil- laries in the papillary dermis and vessels in the upper reticular dermis [2]. A recent case report of congenital plantar AH showed a white thin scale and a reticulated surface with no visible acrosyringia opposing the typical dermoscopic acral pattern [3]. Our study revealed different dermoscopic findings than previously published: A fine white pseudonetwork and elon- gated whitish structures in a “raindrop pattern” found in those patients with longstanding AH and could be correlated with the increasing collagen proliferation and thickening. Thus in our case of 2-weeks’ onset AH, only a yellowish-red blush and red dots with peripheral step-like scales were dis- tinguishing. References 1. Kanitakis J, Lora V, Balme B, Roby J. Premalignant circum- scribedpalmar hypokeratosis: a new form of circumscribed palmar hypokeratosis? Case report and literature review. Der- matology. 2010;220(2):143-146. DOI: 10.1159/000264607. PMID:19955702. 2. Nishimura M, Nishie W, Nakazato S, Nemoto-Hasabe I, Fujita Y, Simizu H. Circumscribed palmar hypokeratosis: correlation between histopathological patterns and dermoscopic findings. Br J Dermatol. 2012;167:221-222. DOI: 10.1111/j.1365- 2133.2012.10855.x. PMID:22283364. 3. Bassi A, Oranges T, Massi D, Piccolo V, Mazzatenta C, Neri I. Congenital circumscribed plantar hypokeratosis. Int J Derma- tol. 202059(10):e367-e369. DOI: 10.1111/ijd.14967. PMID: 32516442.