An Atypical Case of Alopecia Areata

Summary: Atypical alopecia areata (AA) biopsy findings have been reported in viral illnesses. Here we describe a 52-year-old female who experienced sudden hair loss following COVID-19 infection. Scalp biopsy demonstrated atypical perifollicular dense mixed infiltrate with prominent follicular destruction at all levels of the follicle, foreign body giant cells, and impending naked hair shaft formation. The histopathological differential diagnoses included folliculotropic mycosis fungoides, lupus, and lichen planopilaris. The absence of atypia in lymphocytes, non-clonal ratio on immunohistochemical stains and equivocal T-cell gene rearrangement excluded mycosis fungoides, while the absence of interface dermatitis and follicular inflammation ruled out of lupus and lichen planopilaris. Excluding these and other clinicopathological mimics, a diagnosis of AA was made. Additionally, the patient successfully responded to treatment with baricitinib, further supporting our diagnosis. To the best of our knowledge, this is the first report of foreign body giant cells and granulomatous inflammation identified in a case of AA. Although causality between Covid-19 and AA cannot be definitively established, it is theorized that the T-cell mediated immune response in viral infections may trigger antibody cross-reactivity with the hair proteins in susceptible patients. Awareness of unusual histopathological patterns in virally induced AA is important for timely diagnosis and management.