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Prurigo pigmentosa: A case of the “keto rash”

        Prurigo pigmentosa (PP) is a rare inflammatory dermatosis that was first described by Nagashima in 1971. PP is characterized by a pruritic eruption of erythematous papules and papulovesicles on the back, chest and neck. It is thought that PP arises in certain ketotic states due to ketone body deposition in the vasculature leading to neutrophil-mediated, perivascular inflammation. To date, about 300 cases have been reported in literature, largely in the Japanese population. Less than 20 cases of PP have been described in the United States. Thus, we describe a case of 37-year-old male who presented with a 6-day history of a pruritic rash on the abdomen, chest, and back after beginning a ketogenic diet 3 weeks prior to the eruption. On presentation, the patient had already failed trials of triamcinalone 0.1% cream and loratidine 10 mg daily. The patient declined biopsy and treatment with doxycycline, but he agreed to increase his carbohydrate consumption to 50 g/day. At one month follow-up, his rash had resolved leaving behind macular, reticulated areas of hyperpigmentation. Given the growing popularity of the ketogenic diet and countless references to the “keto-rash” on public blogs and sites, we present this case to (1) bring awareness to the condition, (2) discuss the pathogenesis and histopathological findings, and (3) present treatment options.
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