Circumscribed palmoplantar hypokeratosis: report of two Brazilian cases

Circumscribed Palmar Hypokeratosis With Superimposed Actinic Keratosis

A man in his late 70s with a history of psoriasis and non-melanoma skin cancer presented with a progressive rash on his right thenar eminence. He first noticed it about one year ago. He denied any pruritus in the affected region but did note some overlying skin breakdown. He had used topical betamethasone and calcipotriene cream in the past with minimal improvement. Physical examination revealed a pink atrophic plaque with linear hyperkeratotic borders and central fissuring on the right thenar eminence extending into the first webspace. A shave biopsy revealed hypokeratosis with a rim of surrounding hyperkeratosis and associated parakeratosis, basal keratinocyte atypia, and lichenoid inflammation. These histopathological features were consistent with circumscribed palmar hypokeratosis and central actinic keratosis. Circumscribed palmar hypokeratosis is often considered a benign entity, but there have been reports suggesting an association with premalignancy. The decision was made to treat with 5-fluorouracil and calcipotriene cream twice daily for six weeks. At his two-month follow-up, he endorsed a robust reaction, which was further suggestive of premalignant change. He had a near-complete resolution of the rash. This case features circumscribed palmar hypokeratosis and suggests a novel treatment option for patients who develop concomitant actinic keratosis.

Circumscribed palmoplantar hypokeratosis

Circumscribed palmoplantar hypokeratosis (CPH) is a rare acquired dermatosis first described in 2002. It affects mostly the thenar or hypothenar eminences of the palm of middle-aged or elderly women and manifests clinically with sharply limited, annular erythematous plaques with a depressed surface, rimmed by a slightly raised, keratotic border. Microscopically, circumscribed palmoplantar hypokeratosis shows a sharp decrease of the horny layer thickness, with few, if any, associated changes (parakeratosis, dermal inflammation). Despite a characteristic clinical and microscopic aspect, the disease remains poorly known, as does its pathogenesis, even if several hypotheses have been proposed (clonal epidermal malformation, disorder of epidermal differentiation/keratinization and/or desquamation, human papillomavirus- or trauma-induced disease). Several therapies have been proposed with varying results, the best ones achieved with surgical excision; however, because the disease is benign, intervention is optional. © 2020 Elsevier Inc. All rights reserved.