Systematic review of Flegel disease: clinical presentations, associations, diagnostic pitfalls, and management challenges.

Flegel's disease (FD), also known as hyperkeratosis lenticularis perstans, is a rare benign hyperkeratotic dermatosis primarily affecting middle-aged individuals, with a slight female predominance. It presents as small, keratotic papules, often on the lower extremities. The pathogenesis of FD remains uncertain, with proposed mechanisms including genetic predisposition and primary keratinization disorders. Histopathologically, FD is characterized by discrete hyperkeratosis, parakeratosis, thinning or absence of the stratum granulosum, and lichenoid infiltrates in the papillary dermis. Dermoscopic findings such as scaly white and brownish structureless areas can assist in diagnosis. A key point of discussion is the potential overlap between FD and Kyrle disease (KD), as both conditions share similar clinical features, though distinctions exist. FD remains challenging to treat, with no standardized or evidence-based therapeutic guidelines. Various treatment modalities have been attempted, including emollients, topical corticosteroids, retinoids, vitamin D analogs, 5-fluorouracil (5-FU), phototherapy, and ablative techniques like laser therapy and cryotherapy. This systematic review consolidates current knowledge on FD, emphasizing the need for further research to clarify the pathogenesis, genetic underpinnings, and effective management strategies. Understanding FD's distinct features and treatment challenges will aid dermatologists in accurate diagnosis and patient-centered care.