Atraumatic rupture of the gastrocnemius muscle after corticosteroid administration in a dog

A 6-year-old spayed female Shetland Sheepdog was referred for evaluation of lameness, muscle atrophy, and a partial plantigrade stance of the right hind limb of 5 weeks' duration. Without history of trauma, atraumatic rupture of the right gastrocnemius muscle was diagnosed. Surgical repair was unsuccessful. The dog then developed signs of hyperadrenocorticism. Results of ACTH stimulation and low-dose dexamethasone suppression tests were consistent with iatrogenic adrenal suppression. One deleterious effect of excessive use of corticosteroids on muscle and connective tissue is degenerative myopathy. Steroid-induced myopathy with subsequent rupture of the gastrocnemius muscle was suspected in this dog. Clinical signs of myopathy most often develop with use of triamcinolone acetonide; therefore, care should be taken when administering this and other corticosteroids.