Case summary A 2-year-old female neutered domestic shorthair cat presented with an 18-month history of intermittent lameness on all four limbs. The cat was markedly lame on all four limbs. There was alternation between toe-walking on the forelimbs with a hunched posture and using the dorsal aspect of the carpi to walk on. The cat would hiss repeatedly when walking and would lie down tentatively, appearing happier and less painful when lying. When not lying, the cat preferred to sit back on the hindlimbs and non-weightbear on the forelimbs (the so-called kangaroo stance). Physical examination detected pain on palpation of the calcaneus bone and Achilles tendon bilaterally, and general resentment to handling. Investigations revealed an elevated creatine kinase, a positive Toxoplasma gondii IgG titre, toxic neutrophilic inflammation within the Achilles tendon bursae, electromyography and nerve conduction velocity studies consistent with a diffuse muscular disease, and histopathology of the muscle consistent with a chronic and diffuse myopathy. Arthrocentesis samples and an antinuclear antibodies titre were normal. Prior treatment with meloxicam had been ineffective. A 6-week course of clindamycin was prescribed; an improvement was seen within 3 days and clinical resolution at 3 months. The cat remained clinically normal after 20 months.

Relevance and novel information To our knowledge, there have been no previously published reports of histopathologically confirmed myopathy as a result of T gondii in cats. This report suggests toxoplasmosis should be considered as a differential diagnosis in cats with myopathies or lameness in the absence of other causes.