Subacute gracilis myopathy presenting as mass lesions in two Belgian Malinois dogs

Abstract Two male, entire Belgian Malinois dogs, ages 4 and 7 years, presented with firm, intramuscular masses in the medial left thigh. The 7‐year‐old dog presented with a Grade I/V left pelvic limb lameness. Fine‐needle aspiration of each dog revealed mesenchymal cells with few mixed inflammatory cells, which were concerning for underlying neoplasia. Computed tomography findings included hypoattenuating mass lesions within the gracilis muscles on pre‐contrast images with strong peripheral contrast enhancement. Histopathology showed reactive fibrosis accompanied by mild inflammation and chronic haemorrhage. In both cases, the final diagnosis was inflammatory gracilis myopathy. Follow‐up medical records for each dog indicate that the mass lesions were no longer detectable on palpation of the affected limb, and the 7‐year‐old dog was no longer lame. No follow‐up imaging was performed. This is the first report of gracilis myopathies forming rim‐enhancing mass lesions on computed tomography with cytology that may be confused as neoplasia.