Young cat with muscle stiffness and missing sarcoglycan proteins

Abstract

Case summary: A 1-year-old male castrated domestic shorthair cat presented for chronic mobility decline and muscle stiffness, first noted at 3 months of age, and persistently elevated serum creatine kinase levels (>19,000-53,000 IU/L). Clinical examination revealed macroglossia and selective hypertrophy of cervical and appendicular muscles. Neurologic evaluation indicated a myopathic gait without pain or neurologic deficits. Muscle biopsy was supportive of muscular dystrophy and immunohistochemistry demonstrated loss of the sarcoglycan complex with complete absence of all tested sarcoglycan proteins, consistent with a diagnosis of sarcoglycan-deficient muscular dystrophy. These findings contrast prior feline reports which were mostly limited to reduction or absence of β-sarcoglycan on immunostaining without overt clinical evidence of muscular dystrophy. A follow-up echocardiogram revealed mild to moderate right ventricular changes without indications for treatment. At two months post-diagnosis, the patient remained clinically static, suggesting a relatively slow progression despite absent sarcoglycan expression. Relevance and novel information: This case represents the first reported feline sarcoglycanopathy characterized by absence of all tested sarcoglycan subunits on immunohistochemistry and concurrent presentation of classic Duchenne-like muscular dystrophy signs, including macroglossia and muscular hypertrophy. It expands the phenotypic spectrum of muscular dystrophies in cats, underscoring parallels to limb-girdle muscular dystrophies in humans and dogs. Given the cat’s static clinical course and diagnostic overlap with dystrophinopathies, this case suggests sarcoglycan-deficient muscular dystrophy in cats may present with a broader spectrum of severity than previously appreciated. The findings support the potential utility of feline sarcoglycanopathies, when phenotypically consistent with forms appreciated in other species, as spontaneous animal models for comparative medical research.