Epidermolytic hyperkeratosis within infundibular cysts.

Epidermolytic hyperkeratosis (EH) is a well-described histopathologic pattern characteristic of bullous congenital ichthyosiform erythroderma, an autosomal dominant genodermatosis. It is also noted in cutaneous disorders where mosaicism leads to containment of the clinical and histopathologic changes. EH has been observed as an incidental finding in tissue adjacent to and within lesions such as nevi, scars, malignant melanoma, squamous cell carcinoma, basal cell carcinoma, and seborrheic keratoses. We present two cases of EH within infundibular type follicular cysts, a rare finding only once otherwise reported in 1978.