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

ABSTRACT

Background

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.

Methods

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.

Results

Thirty-two confirmed patients were enrolled from 2002 to 2013. Their ages ranged from 11–79 years with a female predominance. Patient lesions were primarily reddish-brown and located on the back. Twenty-five 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 to control groups with either non-inflammatory (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.

Conclusions

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.

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