Post-injection alopecia

This localized alopecia occurs at the injection site area after rabies vaccine or injection of long-acting corticosteroids or progestational compounds.

The post-rabies vaccine-induced alopecia most often is associated with an inflammatory panniculitis and/or vasculitis reaction, in addition to alopecia (Photos 3 and 4).

Breeds at risk for the rabies vaccine-associated alopecia include toy or small-breed dogs, especially Poodles, but also Bichon Frises, Shih Tzus, and Yorkshire and Silky Terriers. A hypersensitivity reaction to the subcutaneous injection of the vaccine is thought to be responsible for clinical signs. Signs develop two to four months after vaccination and consist of an alopecic patch at the injection site. Erythema, scaling, skin thickening and hyperpigmentation may develop, and alopecic patches or plaques may enlarge over time.

Photo 4: Close-up view of alopecic patch in Photo 3.

With the other injection reactions, two to four months after corticosteroid or progestational medication injection, the skin becomes atrophic, thin and hypo pigmented, but no inflammation is present.

Differential diagnoses include localized demodicosis, dermatophytosis, superficial pyoderma, and alopecic aerate. Diagnosis is made by history, clinical signs and histopathology. Histopathology reveals hair follicle, dermal, and adnexal atrophy with the corticosteroid/progestational injection form; and panniculitis, vasculitis, and follicular atrophy with rabies-vaccine-induced alopecia.

Treatment for the non-inflammatory injection reactions is not required.