Prurigo pigmentosa following a ketogenic diet: a case report.

A 19-year-old female of South Asian descent presented with a three-day history of pruritic, clustered papules and vesicles on her abdomen, associated with significant pruritus and intermittent pain. She commenced a ketogenic diet four days prior to the emergence of the rash. Histopathological and clinical findings were in keeping with prurigo pigmentosa, an uncommon dermatosis characterised by pruritic, erythematous papules and vesicles presenting reticulated on the back, chest and neck. Prurigo pigmentosa may be distinguished from many other skin lesions by its reticular pattern. Its pathogenesis is unknown, but it has been hypothesised to be induced by a state of ketosis. Clinicians should therefore be aware of its association with the increasingly popular ketogenic diet. This dermatosis responds well to tetracyclines and has an excellent prognosis. In the patient with ketosis-induced prurigo pigmentosa, administration of insulin or an increase in carbohydrates can also resolve symptoms.