Clinical and Histopathological Characteristics of Prurigo Pigmentosa: A Case Series

Abstract

Introduction: Prurigo pigmentosa (PP) is a rare inflammatory skin disease, first described in 1971 in Japan. The condition is characterized by the abrupt appearance of pruritic, erythematous, maculopapular lesions that typically resolve within several days to weeks, resulting in reticulated hyperpigmentation.

Objective: This study aimed to retrospectively evaluate six cases of prurigo pigmentosa in light of clinical and histopathological features and treatment responses.

Methods: This retrospective study was performed at the Department of Dermatology, Bursa Uludag University Faculty of Medicine, Bursa, Türkiye, from 2022 to 2025. Six patients were included in the study, and their demographic characteristics, presenting complaints, clinical and histopathological findings, laboratory results, and treatment responses were assessed.

Results: Six patients with prurigo pigmentosa were evaluated. All presented with symmetrical, pruritic erythematous eruptions on the trunk and back. Three had a history of ketogenic diet or rapid weight loss. Five patients received oral doxycycline (100–200 mg/day) and demonstrated marked clinical improvement. One patient initially treated with corticosteroids showed worsening and was switched to doxycycline. Histopathology revealed spongiotic dermatitis (N=3), eosinophilic infiltration (N=2), and interface dermatitis (N=1). Elevated serum IgE levels were detected in two cases.

Conclusion: In conclusion, prurigo pigmentosa should be suspected in young patients with symmetric pruritic eruptions and a history of ketosis. Awareness of its variable histopathological findings and its strong association with dietary or metabolic triggers is essential to timely diagnosis. The rapid and consistent response to tetracycline-class antibiotics, particularly doxycycline, underscores their value as both a diagnostic aid and a preferred therapeutic option.