Double Trouble in Porokeratosis: Exploring Coexistent Porokeratosis Ptychotropica and Mibelli in Four Patients

Dear Editor, Porokeratosis is a disorder of epidermal keratinization characterized clinically by annular plaques with thready borders and histologically by cornoid lamellae. Porokeratosis ptychotropica is a rare variant characterized by persistent psoriasiform plaques on the intertriginous areas. We describe four patients who developed lesions in the groin, scrotum, gluteal cleft, and perianal area. Skin biopsy revealed invagination of the epidermis with focal hypogranulosis consistent with cornoid lamellae. Clinical and histologic findings were suggestive of porokeratosis ptychotropica and porokeratosis of Mibelli. Patients were treated with oral isotretinoin and topical tretinoin cream resulting in slight improvement of the lesions. We report these cases to highlight the rarity of porokeratosis ptychotropica and its coexistence with porokeratosis of Mibelli. Patient 1: A 32-year-old man presented with raised lesions in the perianal and inguinal region for 4 years. Three hyperpigmented asymptomatic verrucous plaques measuring 0.5 × 1 cm with irregular borders and central crusting were present on both inguinal regions [Figure 1a]. A 5 × 5 cm plaque on the gluteal cleft and a 2 × 3 cm plaque on the perianal area were noted, both associated with crusting, scaling, and ulceration. [Figure 1b]. Two asymptomatic annular plaques measuring 1 × 1 cm with a thready border, central atrophy and clearing were present on the scrotum [Figure 1c].Figure 1: (a) Patient 1 with crusted, scaly psoriasiform plaques on the inguinal region. (b) Patient 1 with crusted, scaly psoriasiform plaques in the gluteal cleft and around the perianal region. (c) Patient 1 with hyperpigmented annular plaques with a thready border on the scrotal skinPatient 2: A 46-year-old man presented with multiple well-defined hyperpigmented annular plaques on the mid- thigh, groin, scrotum, and shaft of the penis for 2 years [Figure 2a].Figure 2: (a) Patient 2 with a hyperpigmented annular plaque with a thready border on the groin and the shaft of the penis. (b) Patient 3 with a hyperpigmented annular plaque with a thready border on the groin. (c) Patient 4 with a hyperpigmented annular plaque with a thready border on the penoscrotal areaPatient 3: A 37-year-old man presented with multiple well-defined hyperpigmented annular plaques on the groin and scrotum for 5 years [Figure 2b]. Patient 4: A 42-year-old man presented with multiple well-defined hyperpigmented annular plaques on the groin and penoscrotal area for 2 years [Figure 2c]. Laboratory tests were done to rule out liver failure, chronic renal disease, hepatitis C, and human immunodeficiency virus (HIV) infection, and the results were within normal limits. Skin biopsies done from lesions on the groin, scrotal, and perianal area revealed acanthosis and invagination of the epidermis lined by columns of parakeratotic cells with focal hypogranulosis, consistent with cornoid lamella [Figure 3a, 3b]. Clinical and histologic findings were suggestive of porokeratosis ptychotropica on the gluteal cleft and groin and porokeratosis of Mibelli on the scrotum. All four patients were treated with oral isotretinoin 0.5 mg/kg daily and tretinoin cream 0.04% applied alternate nights on lesions, resulting in slight improvement of the lesions after 3 months.Figure 3: (a) Histopathology of lesions on scrotal skin shows epidermal acanthosis, invagination of epidermis lined by columns of parakeratotic cells with focal hypogranulosis consistent with cornoid lamellae (Hematoxylin and eosin, 100×). (b) Histopathology of lesions on the groin and gluteal cleft shows multiple newly developing epidermal invaginations (blue arrows) with focal hypogranulosis consistent with multiple cornoid lamellae (Hematoxylin and eosin, 400×)Porokeratosis comprises a group of epidermal keratinization disorders characterized by annular plaques with hyperkeratotic ridge-like thready borders and an atrophic center that expands centrifugally, resembling the Great Wall of China.[1] It was wrongly named porokeratosis because the cornoid lamella was initially described as being present on the sweat pore, a fixed structure that cannot expand peripherally. Variants include disseminated superficial actinic porokeratosis, porokeratosis of Mibelli, linear, punctate, and palmoplantar porokeratosis. Porokeratosis ptychotropica is a relatively new and rare variant of porokeratosis. It was first reported in 1985 by Helfman and Poulos as reticular porokeratosis affecting the genital region.[1] In 1995, Lucker et al. described porokeratosis ptychotropica derived from the words ptyche (fold) and trope (to turn) to denote its flexural distribution.[2] In 2010, Takiguchi et al.[3] reported a series of 22 patients of porokeratosis ptychotropica, 90% of whom were men, with lesions predominantly involving the genitogluteal region. There is only one reported case of coexisting porokeratosis ptychotropica (perianal) with porokeratosis of Mibelli (buttocks) in a 47-year-old Chinese man.[4] Risk factors include ultraviolet radiation, repetitive trauma, chronic renal failure, hepatitis C, and immunosuppression, although the exact etiology is unclear. It usually has an indolent course over 5-10 years, typically presenting around the 5th decade of life, predominantly in males. It is characterized by pruritic, verrucous hyperkeratotic plaques on the intertriginous areas, mostly involving the gluteal cleft, with extension to the buttocks as satellite papules. Unlike other variants, it is pruritic and lacks a classic elevated, thready border. In Patient 1, there were two solitary plaques asymmetrically located around the gluteal cleft, with no satellite lesions. Histology shows epidermal acanthosis, invagination of the epidermis lined by columns of parakeratotic cells, focal hypogranulosis, and multiple cornoid lamellae. Histology helps exclude other differential diagnoses like psoriasis, condyloma accuminata, and lichen sclerosus. The word ptyche in porokeratosis ptychotropica indicates fold or flexure. A lesion of porokeratosis on the scrotum should not be classified under porokeratosis ptychotropica since the scrotal region is not a fold or flexural area. Many lesions of porokeratosis of Mibelli can also be found in the genital region without being classified under porokeratosis ptychotropica, especially when they present as annular lesions with a keratotic ridge and central atrophy. They are classified under porokeratosis ptchyotropica only if they become hyperkeratotic or verrucous plaques. Some researchers have proposed that porokeratosis ptychotropica may represent a clinical end stage of porokeratosis of Mibelli modified by local factors like lichenification or koebnerization. While the scrotum is not a classic flexural area, it shares the environmental conditions of skin folds and, lies within the intertriginous region. When affected by verrucous, chronic porokeratotic plaques, it is best classified under the clinical and histologic spectrum of porokeratosis ptychotropica. Treatment is challenging as lesions are refractory to treatment and often relapse. Treatment options include topical corticosteroids, vitamin D analogues, calcineurin inhibitors, topical and oral retinoids, 5-fluorouracil, imiquimod, CO2 laser, and photodynamic therapy.[5] Kawakami and Mitsui[6] reported resolution of lesions with topical 5% imiquimod. Malignant transformation in porokeratosis is most commonly reported as invasive squamous cell carcinoma (SCC), followed by SCC in situ and basal cell carcinoma. Risk factors include large size, chronicity, and extremity involvement.[7] Risk of malignant transformation is approximately 1.7%; hence, early detection and periodic follow-up are crucial.[8] In summary, porokeratosis ptychotropica remains a challenging diagnosis due to its rarity and is difficult to treat, given its nature of recurrence and predilection for malignant transformation. We report these cases to underscore the rarity of porokeratosis ptychotropica and its coexistence with porokeratosis of Mibelli. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Use of artificial intelligence (AI) The preparation of this manuscript was carried out entirely by the authors without the use of artificial intelligence technologies.