Suspected muscular pseudohypertrophy in a dog: An atypical presentation of hypothyroidism

Abstract A 4‐year‐old intact male border collie was presented with stiffness, reluctance to move and stridor. The owners reported a progressive muscle swelling, eventually restricting the dog's movement. Thyroid function tests revealed low free and total thyroxine levels with elevated thyrotropin (thyroid‐stimulating hormone) levels, indicating primary hypothyroidism. Computed tomography imaging showed marked muscle development without contrast enhancement. Muscular hypertrophy or pseudohypertrophy secondary to hypothyroidism was then suspected. Hormonal supplementation was implemented, leading to complete resolution of clinical signs within 2 months. Four years later, the dog remained well stabilised with no recurrence. This case report highlights an atypical manifestation of canine hypothyroidism with suspected muscle pseudohypertrophy, suggesting that hypothyroidism should be considered as a differential diagnosis of stiffness and reluctance to move with associated muscular hypertrophy or pseudohypertrophy in dogs.