Follicular Psoriasis: An Uncommon Variant of Psoriasis

Summary: Follicular psoriasis (FP) is an uncommon and possibly underreported variant of psoriasis with few cases reported to date. While typical plaque psoriasis (psoriasis vulgaris) demonstrates well-demarcated, pink plaques with micaceous scale clinically, FP manifests with more discrete, follicular accentuated papules. Histologically, lesions of FP are characterized by typical features of psoriasis (acanthosis, hypogranulosis, parakeratosis, and neutrophils in stratum corneum) with folliculocentric hyperkeratosis/plugging in comparison to plaque psoriasis. Some lesions may also demonstrate erythrocyte extravasation appearing with a purpuric base clinically. Herein, we describe a case of FP in a 54 year-old female presenting with a chronic history of an asymptomatic rash characterized by pink, 1-2 mm sized follicular based keratotic papules discretely scattered and coalescent into ovoid 1-2 cm sized plaques of the upper and lower extremities. Punch biopsy of a right upper arm plaque demonstrated acanthosis with follicular based hypogranulosis, plugging, parakeratosis and neutrophils in the stratum corneum consistent with FP. Lichen spinulosus and pityriasis rubra pilaris were considered in the histopathologic differential; however, psoriasis was favored in presence of neutrophils in the stratum corneum. Patient was initiated on topical triamcinolone 0.1% cream twice daily to involved skin.