Follicular Psoriasis

Psoriasis is a common chronic inflammatory papulosquamous dermatosis of unknown etiology. The prototype – psoriasis vulgaris – is characterized by erythematous, scaly plaques, typically occurring on the extensor surfaces including the scalp. Other clinical subtypes such as guttate, pustular, erythrodermic, verrucous, inverse, and palmoplantar psoriasis are also well recognized.1 In contrast, follicular psoriasis is an uncommon diagnosis and probably the least well-known subtype of psoriasis. It has only been reported in two small case series in the English literature.2,3 Herein, we report a case of follicular psoriasis to raise awareness of this rare entity. Our patient is a 46-year-old diabetic AfricanAmerican woman who presented with a two-year history of pruritic, follicularly-based, hyperkeratotic papules on the scalp, neck, back, and extremities (Figures 1 and 3). The papules measured less than 0.3 cm in diameter, and occurred both singly and in small clusters. No significant erythema was observed; however, some lesions were associated with post-inflammatory hyperpigmentation. The patient had no history of psoriasis and lacked other classical lesions of psoriasis. Her renal function was normal. Screening for anti-nuclear and antiENA (extractable nuclear antigens) antibodies was negative. The clinical differential diagnosis included perforating disorder, sarcoidosis, and verrucous lupus erythematosus. Multiple biopsies were obtained and showed the primary pathologic process to be localized to the follicular infundibula (Figure 4), which were distended by excrescent layers of parakeratotic scale admixed with neutrophils (Figure 2). The perifollicular epidermis showed mild psoriasiform hyperplasia, while the rest of the epidermis was unremarkable (Figure 4). The infundibular Fig. 1. There are grouped papules on the forearm. Many lesions appear to contain a central keratotic plug. (Courtesy of Dr. Thy Thy Do, Department of Dermatology, University of Michigan, Ann Arbor, MI)