Porokeratosis Ptychotropica: Dermoscopy, Reflectance Confocal Microscopy, and Histopathological Correlation.

Porokeratosis ptychotropica (PP) is a rare variant of porokeratosis characterized by pruritic, symmetrical, red-brown verrucous papules, and plaques most commonly localized within the gluteal fold. Herein, we report the clinical, dermoscopy, and reflectance confocal microscopy (RCM) aspects of a case of PP in a 63-year-old Caucasian woman along with histopathological correlation. Both dermoscopy and RCM were able to recognize the cornoid lamella, the histopathological clue shared by all clinical variants of porokeratosis. These non-invasive techniques may help in the differential diagnosis with other inflammatory/infectious and neoplastic disorders that may clinically resemble PP, but show distinct patterns. Copyright:

Introduction

Porokeratosis ptychotropica (PP) is a rare verrucous form of porokeratosis, a group of disorders also including porokeratosis of Mibelli, porokeratosis plantaris, palmaris et disseminata, punctate porokeratosis, linear porokeratosis, and disseminated superficial actinic porokeratosis.[12] The etiology of PP is not definitely established. Predisposing factors include repetitive frictional trauma as well as genetics and immunosuppression.[2]

PP is more common in males in their 40s and is characterized by pruritic, symmetrical, red-brown verrucous papules, and plaques most commonly localized within the gluteal fold.[3] The lesions tend to coalesce centrally and expand peripherally, and sometimes exhibit a slow regional extension to groins, upper thighs, and genitalia.[45]

PP presents a chronic course, and it is generally refractory to treatments that include topical corticosteroids, vitamin D analogs and calcineurin inhibitors, topical and oral retinoids, cryotherapy, 5-fluorouracil, imiquimod, CO2 laser, and photodynamic therapy.[56] A malignant transformation into an invasive squamous cell carcinoma has been reported.[7] Therefore, a periodic follow-up is recommended.

Herein, we report the clinical, dermoscopy, and reflectance confocal microscopy (RCM) aspects of a case of PP in a woman along with histopathological correlation.

Case History

A 63-year-old Caucasian woman presented with a 3-year history of itching papules located on the gluteal cleft, determining a highly compromised quality of life. The lesions had been previously diagnosed as mycosis and common warts, and were refractory to various treatments including topical antifungals, corticosteroids, and dermabrasion.

Clinical examination revealed, on the gluteal fold and the perianal area, several roundish, hyperkeratotic, brownish papules coalescing in polycyclic plaques with raised borders, measuring 8 × 6 cm, with a symmetric distribution and a tendency to form a “butterfly” shaped plaque [Figure 1].

Figure 1

Symmetrical roundish, hyperkeratotic, brownish papules coalescing to form polycyclic plaques with raised borders, localized over gluteal fold and the perianal area

Routine laboratory investigations were normal, and cultures for bacteria and yeasts resulted negative. At polarized dermoscopy (Illuco IDS-1100®, Tre T Medical, Camposano, Italy), each lesion showed a sharply demarcated, white-yellowish, hyperkeratotic, peripheral rim limiting an erythematous, centre with yellowish and whitish scales, and some globular vessels [Figure 2a]. At handheld RCM (Vivascope 3000®, Mavig GmbH, Munich, Germany), the main aspects consisted of an atypical, honeycombed pattern, and a peripheral abrupt interruption of the epidermis by a well-defined hyperreflective structureless rim surrounding the lesion [Figure 2b].

Figure 2

(a) Polarized dermoscopy (×10): Annular, white-yellowish hyperkeratotic rim (arrows) demarcating a central scar-like area with whitish scales and some globular vessels. (b) Reflectance confocal microscopy: Well-defined, peripheral rim appearing as an amorphous structure (asterisks) abruptly interrupting the epidermis (arrows). (c) Histopathology showing the cornoid lamella (asterisk), epidermal vacuolization, absence of granular cell layer and a slight chronic inflammatory infiltrate (H and E, ×100)

Histological examination of a punch biopsy showed typical keratin-filled epidermal invaginations with angulated parakeratotic tiers (cornoid lamellae). Under the corneal layer, the epithelium was vacuolated and devoid of granular cell layer. No epithelial dysplasia or cytoid bodies were observed. In the superficial dermis, a slight non-specific perivascular chronic inflammatory infiltrate was observed [Figure 2c].

Based on clinical, instrumental, and histopathological features, the diagnosis of PP was established. The patient was treated with topical corticosteroids and retinoids. At six months' follow-up, a poor improvement of the lesions with a moderate decrease of itching was observed.

Discussion

The term PP was introduced by Lucker et al.[8] in 1995. They used the term 'ptychotropica' from the Greek words “πτυχή” (fold) and “τροπικός” (turning) to describe the characteristic involvement of the body folds. Less than 50 cases have been reported in the literature,[2347910111213] but probably the disease is misdiagnosed. PP may be clinically suspected especially when it appears with a characteristic butterfly shaped, scaly plaque with a raised rim. The lesions are generally itching, predisposing to frequent scratching, friction, and chronic inflammation, as in our patient.

Histopathology generally confirms the diagnosis of PP showing multiple cornoid lamellae, that is columns of tightly packed parakeratotic cells settling within depressions of the upper epidermis. Beneath the cornoid lamellae, focal basal layer degeneration and disappearance of the granular layer with some dyskeratotic cells, are typically observed.[1011] Cornoid lamella is a histopathological finding shared by all clinical variants of porokeratosis.

Dermoscopy of PP has been described in three cases involving the gluteal and scrotal area.[111213] The main observed feature, as in our patient, was a characteristic, hyperkeratotic rim demarcating the lesions.[111213] A typical annular, single or double, white-yellowish hyperkeratotic rim demarcating a central scar-like area is also observed in other forms of porokeratosis.[14]

RCM findings of PP have not been described so far. In our case, we observed a loss of the normal honeycomb pattern and the presence of a distinct, peripheral rim appearing as a hyper- and/or hyporeflective amorphous structure abruptly interrupting the epidermis, a finding consistent with the histology of cornoid lamella. Similar aspects are also reported in disseminated superficial actinic porokeratosis[151617] and porokeratosis of Mibelli.[18]

In our patient, the unusual clinical presentation of keratotic lesions, in and around the intergluteal fold, along with the recognition of the cornoid lamella both at dermoscopy and RCM, were very suggestive of PP as later confirmed by histopathology. Interestingly, both non-invasive procedures may help in the differential diagnosis with other inflammatory/infectious and neoplastic disorders that may clinically resemble PP such as psoriasis, tinea corporis, hypertrophic lichen planus, lichen simplex chronicus, Darier's disease, granuloma annulare, common warts, epidermodysplasia verruciformis, and seborrheic keratosis,[1] but that show distinct patterns. Finally, dermoscopy and RCM might also play a role in the early diagnosis of potential skin cancer arising from PP.[7]

Financial support and sponsorship

This work was supported by the University of Catania, Department of General Surgery and Medical-Surgical Specialties - Research Program “PIACERI 2020/2022 - Starting Grant”. P.I. Prof. Francesco Lacarrubba.

Conflicts of interest

There are no conflicts of interest.