Miscellaneous annular diseases.

Annular lesions represent a unique macro-morphologic pattern in various skin disorders that may be found in pityriasis rotunda, elastosis perforans serpiginosa, subacute nodular migratory panniculitis, keratolysis exfoliativa, neutrophilic eccrine hidradenitis, hemophagocytic lymphohistiocytosis, and intentionally induced annular lesions. This group is highly heterogenous and variable in clinical presentation. Whereas some are benign self-limiting disorders like pityriasis rotunda, others such as hemophagocytic lymphohistiocytosis follow a chronic course or have a potential of being life-threatening. Epidemiology, pathogenesis, histopathology, clinical presentation and diagnosis, differential diagnosis, and treatment are discussed.