A Systematic Review of Follicular Psoriasis: A Unique but Under-Recognized Entity.

Background: Follicular psoriasis (FP) is a rare and under-recognized subtype of psoriasis that affects hair follicles and can be frequently misdiagnosed due to its unique presentation.

Objective: We aimed to analyze the frequently reported clinical, histological, and dermatoscopic features of FP, as well as their treatment options.

Methods: We conducted a systematic review of the PubMed/MEDLINE database using the search terms "follicular" and "psoriasis." Fourteen studies were included yielding information on 44 patients (27 adults [61.4%] and 17 children [38.6%]).

Results: Adult FP showed a female predominance (M:F = 1:2.7), frequent involvement of lower extremities (81.5%), association with metabolic syndrome including diabetes mellitus (22.2%), and a predilection for skin of color (SOC:White = 8:1). On the contrary, juvenile FP revealed male predominance (M:F = 1:0.6), frequent involvement of the trunk (41.2%), and exclusive involvement in skin of color (SOC:White = 11:0). In addition to its unique presentation, FP tends to be misdiagnosed due to its low incidence of concomitant psoriasis (31.8%), and rare personal (18.2%) or family history (6.8%) of psoriasis. Reported histopathological features include keratotic plugging, follicular parakeratosis with or without neutrophils, psoriasiform acanthosis, hypogranulosis, and neutrophilic infiltration of follicular epithelium. Dermatoscopic findings include folliculocentric lesions with normal appearing terminal hairs, perifollicular white scale, and various vascular structures.

Conclusion: Once correctly diagnosed, patients with FP showed improvement or resolution of symptoms with various combinations of topical and systemic therapies. Understanding the demographic features and clinical presentations of FP can help address under-recognition of this clinical variant of psoriasis.