J Vet Intern Med. 2026 Jan 21;40(1):aalag006. doi: 10.1093/jvimsj/aalag006.
ABSTRACT
BACKGROUND: A hypertrophic cardiomyopathy phenotype (HCMP) can occur in cats with hyperthyroidism. However, it remains unclear whether other cardiomyopathy phenotypes are also associated with hyperthyroidism in cats.
HYPOTHESIS/OBJECTIVES: Describe the epidemiological, clinical, and echocardiographic findings and cardiomyopathy phenotypes in a large sample of hyperthyroid cats. Compare the echocardiographic features of hyperthyroid cats with HCMP to those of a contemporaneous sample of normotensive euthyroid cats with primary hypertrophic cardiomyopathy (HCM).
ANIMALS: A total of 147 hyperthyroid cats and 112 cats with primary HCM.
METHODS: Retrospective study with review of internal medicine and cardiology service databases (2005-2025).
RESULTS: Most hyperthyroid cats (117/147, 80%) exhibited 1 of the 3 cardiomyopathy phenotypes: HCMP (94/147, 64%), restrictive cardiomyopathy phenotype (RCMP; 20/147, 14%), or nonspecific (3/147, 2%). Hyperthyroid cats with RCMP had significantly higher total thyroxine concentrations (median, 154 nmol/L vs 95 nmol/L) and more dyspnea related to congestive heart failure (80% vs 11%) than those with HCMP (P < .01). A gallop sound was detected in 10% of hyperthyroid cats (14/147), exclusively in those with HCMP (10%, 9/94) or RCMP (25%, 5/20). The end-diastolic left ventricular diameter was higher in hyperthyroid cats with HCMP than in those with primary HCM (P < .01). Subaortic septal hypertrophy was more frequent (95% vs 67%) in cats with primary HCM than in those with hyperthyroidism-associated HCMP (P < .01).
CONCLUSIONS AND CLINICAL IMPORTANCE: The HCMP is the predominant, but not sole, echocardiographic phenotype observed in hyperthyroid cats. The RCMP is the second most frequent phenotype and may reflect a more severe form of hyperthyroidism.
PMID:41742580 | PMC:PMC12908685 | DOI:10.1093/jvimsj/aalag006