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- Is That HCM Permanent? New Data Reveal How Often Myocardial Thickening Reverses in Cats
Is That HCM Permanent? New Data Reveal How Often Myocardial Thickening Reverses in Cats
Vet Q. 2025
Obi Veterinary Education
February 15, 2026
,Keon Kim,Young-Jae Lee,Yoon-Jung Do,Woong-Bin Ro &Chang-Min Lee
Background
Hypertrophic cardiomyopathy (HCM) is the most commonly diagnosed cardiac disease in cats and is characterized by increased left ventricular wall thickness. However, transient myocardial thickening (TMT) has been described in cats presenting with an HCM phenotype, particularly in association with stressors or systemic illness. Differentiating primary (presumed genetic) HCM from reversible myocardial thickening is clinically important for prognosis and management. The study aimed to determine the prevalence of TMT among cats presenting with an HCM phenotype and to describe their clinical and echocardiographic characteristics.
Methods
This retrospective study evaluated cats diagnosed with an HCM phenotype based on echocardiographic criteria at a referral institution. Medical records and serial echocardiograms were reviewed. Cats were classified as having TMT if myocardial thickening resolved or significantly regressed on follow-up echocardiography without HCM-specific therapy. Signalment, clinical presentation, presence of congestive heart failure (CHF), laboratory findings, and echocardiographic measurements were compared between cats with persistent HCM and those with TMT.
Results
A subset of cats presenting with an HCM phenotype demonstrated subsequent resolution of myocardial thickening consistent with TMT, establishing that reversible thickening represents a meaningful proportion of cases. Cats with TMT were generally younger than those with persistent HCM and more frequently had identifiable antecedent stressors or systemic illness at presentation. Echocardiographically, TMT cats had marked but reversible increases in left ventricular wall thickness. Clinical signs, including CHF, were present in some TMT cases but resolved with time and supportive care. In contrast, cats with persistent HCM maintained hypertrophy on follow-up imaging.
Limitations
The retrospective design limited control over diagnostic testing and follow-up intervals. Not all cats underwent standardized re-evaluation, potentially affecting classification. Genetic testing was not uniformly performed, preventing definitive exclusion of primary HCM in all cases. Additionally, referral bias may have influenced case selection.
Conclusions
Transient myocardial thickening accounts for a notable proportion of cats presenting with an HCM phenotype and is characterized by reversible myocardial hypertrophy, often in younger cats and in association with systemic stressors. Serial echocardiographic evaluation is essential to distinguish TMT from primary HCM, as prognosis and long-term management differ substantially between these conditions.
Flowchart illustrating the classification of cats enrolled in the study. A total of 432 cats underwent echocardiographic evaluation, of which 145 were classified as having HCM phenotypes. Among these, 53 cats underwent serial echocardiographic evaluations. Three cats were excluded from further classification due to the identification of hyperthyroidism (n = 2) or reversible pseudohypertrophy (n = 1). The remaining 50 cats were classified into the TMT and HCM groups based on serial echocardiographic findings: TMT group (n = 16) and HCM group (n = 34). Within the TMT group, 14 cats showed complete resolution of myocardial thickening (pure TMT), while 2 cats fulfilled the TMT criteria but maintained an LVWT ≥6.0 mm on follow-up and were designated as TMT on HCM. TMT, transient myocardial thickening; HCM, hypertrophic cardiomyopathy.
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