Compound Follicles in Folliculitis Decalvans Do Not Contain Vellus and Retained Telogen Follicles-A Pilot Histopathologic Series on Polytrichia.

Background: Polytrichia is a common clinical and trichoscopic feature in folliculitis decalvans (FD) that morphologically corresponds to compound follicular structures (CFS) of six or more follicles sharing a single infundibulum, surrounded by fibrosis.

Objectives: To characterize the type of follicles in the CFS in scalp biopsy specimens from FD.

Methods: We retrospectively reviewed 10 scalp biopsy specimens obtained by using the trichoscopy-guided approach from the affected scalp of patients diagnosed with early-stage FD between 2018 and 2023. We assessed the number and type of follicles within the CFS on horizontal sections.

Results: The total number of assessed follicles was 205, out of which 159 were part of CFS. Of those, 156 were terminal follicles (146 anagen and ten telogen), three intermediate, and zero vellus follicles. Other common findings included dense mixed cell infiltrate consisting of histiocytes, plasma cells, lymphocytes, neutrophils, and eosinophils; psoriasiform hyperplasia; and fragmented hair shafts.

Conclusions: We show that CFS in FD are composed largely of terminal anagen follicles. This may help with further understanding of the disease.