Folliculitis in prurigo pigmentosa: a proposed pathogenesis based on clinical and pathological observation

Prurigo pigmentosa is a rare inflammatory dermatosis whose exact etiology is not understood yet. The purpose of this study was to provide evidence of hair follicle involvement in the pathogenesis by analyzing its clinicopathologic features.

Patients who fulfilled both the clinical and histological diagnostic criteria of prurigo pigmentosa were recruited. Their histopathologic findings, clinical features and medical histories were analyzed.

A total of 32 confirmed patients were enrolled from 2002 to 2013. Their ages ranged from 11 to 79 years with a female predominance. Patient lesions were primarily reddish-brown and located on the back. A total of 25 patients (78%) had pathological involvement of hair follicles, either bacterial colonies in the hair follicles (21/32, 66%), folliculitis (8/32, 25%) or perifolliculitis (15/32, 47%). There was a significantly higher proportion of patients with hair follicle involvement compared with control groups with either noninflammatory (5/43, 12%, p < 0.001) or inflammatory skin diseases (12/32, 38%, p = 0.002) on the back. Minocycline was an effective antibiotic treatment either singly or in combination with steroids.

The frequent presence of bacterial colonies along with sequelae of inflammatory changes on biopsy provides new evidence to support the theory that prurigo pigmentosa is a reactive inflammation associated with bacterial folliculitis.