Hyperkeratosis lenticularis perstans (HLP), also known as Flegel disease, is a rare dermatosis of unknown etiology characterized by asymptomatic, small, erythematous to brown, hyperkeratotic papules distributed symmetrically on the distal extremities. Lesions are typically less than 5 mm in diameter, with a predilection for the dorsal surface of the feet and distal lower extremities, typically sparing the palms, soles, and mucous membranes. This chronic condition is more common in women and presents in the fourth to fifth decade of life.

Incidence and prevalence of HLP are difficult to assess given the limited number of cases reported in the literature, which may in part be due to its asymptomatic nature. While some reported cases are sporadic, many are familial. Mutations in the SPTLC1 gene have been found in affected individuals. SPTLC1 encodes serine palmitoyltransferase, which is the initial enzyme in the pathway responsible for sphingolipid production, and disordered sphingolipid production is responsible for the altered membrane-coating granules seen in the epidermis in this condition.