Topical Calcium Thioglycolate for Severe Plantar Hyperkeratosis in Atopic Dermatitis: A Case Report

Palmoplantar hyperkeratosis may arise from hereditary or acquired keratinization disorders or inflammatory dermatoses. We report a 20-year-old woman with Fitzpatrick type VI skin, longstanding atopic dermatitis, and poorly controlled type 1 diabetes mellitus who developed refractory palmoplantar hyperkeratosis. Her disease was most pronounced on the soles, where a florid, diffuse, thick, yellowish, verrucous-appearing hyperkeratotic phase improved over the course of treatment to residual lichenified, acanthotic, fissured plaques on the central palms and insteps. Histopathology demonstrated spongiotic dermatitis, and the overall clinical and histologic findings were most consistent with hyperkeratotic palmoplantar eczema, the florid keratotic phase representing the severe end of this process as it commonly manifests in richly pigmented skin. The condition persisted despite multiple conventional therapies, including topical and oral corticosteroids, oral retinoids, methotrexate, and urea-based keratolytic preparations. Notably, the patient experienced near-complete resolution of the florid plantar hyperkeratosis during off-label use of a calcium thioglycolate-based chemical depilatory, while the residual eczematous plaques persisted. This case highlights a potential adjunctive role for topical depilatory agents in the keratotic phase of refractory hyperkeratotic eczema and contributes to the limited visual documentation of palmoplantar hyperkeratosis in richly pigmented skin.