Abstract
Hidroacanthoma simplex (HAS) was first described in 1956 and not until Kennedy in 1979 was the pigmented hidroacanthoma simplex (PHAS) well-characterized. The first reported case of malignant PHAS was in 1982, with the hypothesis that abnormal melanosome transfer predisposes this lesion to malignancy. There are only seven reported in the literature wherein a porocarcinoma arises within a pre-existing PHAS. Porocarcinoma is often reported on the lower extremities and buttock, but our patient is the first case in the literature of malignant PHAS arising on the head and neck region. Herein, we present an 81-year-old Caucasian male with a past medical history of non-melanoma skin cancer who presented with an irritated flesh-tan flat-topped papule of the left upper nasal sidewall clinically diagnosed as an irritated seborrheic keratosis and treated with cryotherapy. At the following visit two months later, the lesion persisted and became tender. Tangential biopsy was performed, and histopathology was reported as inflamed and irritated seborrheic keratosis. At follow-up four months later, the lesion recurred, was tender to the touch, and was re-biopsied. Histopathology was consistent with malignant transformation of a pigmented hidroacanthoma simplex to invasive porocarcinoma with sarcomatoid transformation. Given the frequent clinical and histopathological misdiagnosis of PHAS as seborrheic keratosis or Bowens disease, and one documented case of advanced metastatic disease, early identification and surgical management is critical. We present a unique case of pigmented PHAS to raise awareness of this rare entity.
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