Progressive increases in creatine kinase (CK) activity in an anorexic cat with necrotizing myopathy

Necrotizing myopathy (NM) is not very often diagnosed in small animals, but it might be underestimated because muscle biopsies are not done routinely. This disease is characterized by muscle necrosis and cats that have this condition may present paresis and increased creatine kinase (CK) activity.

CK is a specific enzyme marker of myofiber damage and a high serological CK activity in anorexic cats is usually associated with muscle catabolism, trauma, prolonged recumbency, hemolysis or hyperbilirubinemia.
A 5-year-old neutered male domestic shorthair cat was presented to the referring veterinarian after a period of marked weight loss and hyporexia. After physical examination and several diagnostic tests, the main abnormalities noted were mild elevation in ALT and CK activity, reduced urine specific gravity and marked hematuria.

The cat was hospitalized over 3 weeks and treated with IV fluid therapy, antibiotics, analgesia, antinausea and antiemetic drugs, a muscle relaxant and nutritional support. As the serum CK activity progressively increased, the cat remained persistently lethargic. When referred to another veterinary hospital it presented a stiff gait but no other neurological abnormalities. At this stage, a provisional diagnosis was made – primary myopathy. Muscle biopsies were collected which led to the diagnosis of an early/mild NM with phagocytosis.

Prednisolone (5mg PO q24h) was initiated, an esophageal tube was placed for feeding and all other medications were discontinued. The cat’s appetite and mobility improved within 2 days. Treatment with anti-inflammatory doses of prednisolone was continued for 5 weeks. CK activity started decreasing and normalized in 6 weeks. It resulted in a good clinical outcome.

Muscle biopsy revealed myonecrosis and ruled out inflammatory, metabolic, and other congenital structural myopathies. Although we cannot exclude the possibility of immune-mediated or drug-induced myopathy, a degenerative myopathy was considered most likely. This case provides evidence that myonecrosis can be a potential consequence of anorexia and abnormal nutritional status in cats.

Chow J., Lam A. and Shelton G.D. (2021) Progressive increases in creatine kinase activity in an anorexic cat with necrotising myopathy. Journal of Feline Medicine and Surgery, Open Reports.
https://doi.org/10.1177/20551169211031790