Ketogenic Diet-induced Prurigo Pigmentosa (the "Keto Rash"): A Case Report and Literature Review.

Prurigo pigmentosa (PP) is a rare inflammatory dermatosis of unknown etiology that primarily affects adolescents and young adults. It is typically characterized by a pruritic eruption of erythematous papules on the trunk and neck that evolves into reticulate hyperpigmentation upon resolution of the inflammatory phase of the rash. It has been associated with various triggers, including the metabolic state of ketosis. Interestingly, the recent increase in popularity of the ketogenic diet for weight loss has led to an increased number of PP cases reported in the literature. We present a case of PP in a 21-year-old Hispanic man, which erupted during strict adherence to a ketogenic diet. We conducted a literature review and identified 19 other cases of PP related to ketogenic diet. While PP has historically been reported primarily in Asia, we found cases occurring in patients of Middle Eastern, Caucasian, Hispanic, Asian, and African descent. On average, the rash presented 31 days after initiating the diet and subsided 18 days after diet cessation. Most cases were treated with an oral tetracycline and resolved with residual hyperpigmentation. We present this information to highlight the increasing association of PP with the ketogenic diet so that early diagnosis and treatment and optimal patient outcomes may be achieved. Dermatologists should be aware of the timing of rash onset and resolution in relation to the diet.