Hyperkeratosis lenticularis perstans (Flegel's disease). Ultrastructural study of lesional and perilesional skin and therapeutic trial of topical tretinoin versus 5-fluorouracil.

Lesional and perilesional skin samples from a 57-year-old man who had hyperkeratosis lenticularis perstans (HLP) (Flegel's disease) were studied by light and electron microscopic examination. Keratohyalin granules were diminished at the center of a fully-developed lesion. In contrast, keratohyalin appeared normal and membrane-coating granules were found in reduced numbers at the edges of the HLP lesion and were easily detected in normal numbers in clinically normal, perilesional skin. The inflammatory infiltrate in the HLP lesion was composed of small lymphocytes, which often displayed nuclei with deep infoldings resembling Sézary cells, and larger histiocytic cells, many of which were in close contact with the lymphocytes. Peripheral blood mononuclear cells did not show an abnormal ultrastructural appearance. Treatment with topical 5-fluorouracil cream led to the disappearance of the HLP lesions, whereas topical tretinoin was ineffective.