Canities Subita after Extreme Trauma Showing Positive Staining for Anti-PD-L1 Antibodies: A New Clue into Etiopathogenesis?

Canities subita has been considered by some authors an acute episode of diffuse alopecia areata in which the sudden whitening is caused by the preferential loss of pigmented hair in this immune-mediated disorder. Clinically, the "salt and pepper" pattern of hair color is the most frequent manifestation of canities subita. However, the exact physiopathology of canities subita is not completely understood. A 69-year-old Caucasian man was referred for the sudden and asymptomatic whitening of the hair on the scalp and eyebrows, without an associated hair loss. The trigger was the death of his brother. Hair whitening appeared 24 h after the event. He reported a history of alopecia areata in plaques on the scalp, with spontaneous complete resolution in 2006. The physical examination showed full whitening hair on the scalp and eyebrows. Eyelashes were not affected. The pull test was negative, and the patient denied a significant hair loss in the last days. The histopathological study showed several follicle-sebaceous structures in the anagen, and one of them (inset) with a transforming hair bulb. The anterior bulb was surrounded by a lymphocytic inflammatory infiltrate in an advanced stage of transformation to the catagen and incipient scar changes. Immunohistochemistry staining showed a positive anti-PD-L1 antibody expressed in the inflammatory infiltrate. Based on the clinical and histological findings, a diagnosis of canities subita was made. The histopathological study showed a positive staining for anti-PD-L1 antibodies, supporting the role of the immune system in the development of this phenomenon. The interaction between melanogenesis and the lymphocytes warrants further research.