Prurigo pigmentosa: a clinicopathologic study of 16 cases

Background Prurigo pigmentosa is a rare inflammatory disease of unknown origin. It is characterized by the sudden onset of pruritic erythematous papules, usually involving the trunk and neck, which coalesce to form reticulated, mottled patches. Methods We studied 16 patients with prurigo pigmentosa. The patients were selected from those attending the outpatient Department of Dermatology at the Kyung Hee University Hospital from January 2002 to January 2010. All clinical information was retrospectively collected from medical records. The serum concentrations of ketones (acetoacetic acid, 3‐hydroxybutyrate acid [3‐OHBA]) were examined in four patients, and a test for ketone in the urine was performed in 10 patients. Results The age at the time of diagnosis ranged from 18 to 36 years (mean age: 23.5 years), and the female : male ratio was 14 : 2. Skin lesions were almost always characterized by recurrent pruritic erythematous papules that had resolved, leaving a peculiar, reticulate hyperpigmentation. Eight of 16 patients showed a chronological relationship between a prurigo pigmentosa appearance of skin lesions and dieting or fasting. Histopathological findings were either of fully developed lesions (4/16) or late lesions (12/16). Most patients responded well to minocycline treatment. Ketosis was observed in six patients. Conclusions In conclusion, we propose that ketosis was caused by fasting, and that diet may contribute to the pathogenesis of prurigo pigmentosa. Thus, physicians need to warn that excessive fasting can cause prurigo pigmentosa.