Unexpected Extensive Hair Whitening Following Baricitinib Treatment for Alopecia Universalis: A Case Report and Mechanistic Insights.

Alopecia universalis (AU) is a severe form of alopecia areata characterized by the complete loss of scalp and body hair. While Janus kinase (JAK) inhibitors like baricitinib have shown promise in promoting hair regrowth in severe cases of AU, unexpected side effects, such as hair depigmentation, have not been widely reported. We present the case of a young male with AU who experienced progressive and extensive whitening of his scalp and body hair following treatment with baricitinib. After one month of therapy, the patient observed both black and white hairs emerging, which gradually turned entirely white by the second month. Over the course of seven months, the whitening of the hair persisted, with no repigmentation observed. Laboratory tests and clinical evaluations indicated no significant adverse effects, suggesting that baricitinib was well tolerated. Dermoscopic examination revealed predominantly white terminal hairs. While the mechanisms underlying this phenomenon remain unclear, we discuss potential interactions between JAK inhibition and melanocyte function, suggesting that baricitinib's modulation of the JAK-STAT pathway may impact melanogenesis and hair pigmentation. This case highlights the need for further investigation into the effects of JAK inhibitors on hair pigmentation and the potential for hair whitening as an uncommon side effect. Understanding these mechanisms is essential for improving treatment strategies for AU and addressing patient concerns regarding pigmentation changes during therapy.