Widespread, symmetric, noninflammatory alopecia associated with follicular dysplasia in the American red squirrel (Tamiasciurus hudsonicus)

This report describes a unique pattern of alopecia in 8 American red squirrels (Tamiasciurus hudsonicus) from 2013 to 2021. All animals were juveniles; 6 were female and 2 were male. Seven presented between September and November, and one presented in April. All squirrels had widespread, bilaterally symmetric, noninflammatory, well-demarcated alopecia involving the entire trunk and legs and normal hair on their muzzle and dorsal surfaces of their paws. Six months later, a normal hair coat had grown on 2 of the animals, which were littermates. Hair fully grew 2 months later in another animal. Histopathology of the alopecic skin was performed in 7 of 8 animals. The following changes were noted: bent and coiled hairs, perforating folliculitis, melanin clumping, and distortion of hair shafts. Based on features of follicular dysplasia and apparent seasonality, this condition has some similarities to canine seasonal flank alopecia. A genetic etiology is suspected.