Spreading pigmented actinic keratosis. An electron microscopic study.

Spreading pigmented actinic keratosis is a rarely reported premalignant, pigmented, epidermal tumor that can be difficult to distinguish clinically from other benign and malignant pigmented lesions. In an attempt to determine the cause of clinical hyperpigmentation, seven lesions from five patients were examined by light microscopy. Three of these lesions were also examined using electron microscopy. Findings from these studies indicate that hyperpigmentation is due to enhanced melanosome formation and distribution and not to a melanocyte-keratinocyte melanosome transfer block.