Left Ventricular Hypertrophy with Normal T1 Mapping: A Diagnostic Pitfall

Description of Clinical Presentation: A 59-year-old Asian man with hypertension and asthma presented with progressive dyspnea and fatigue over 6–12 months. A systolic murmur was noted. Electrocardiography showed sinus rhythm with left ventricular hypertrophy. Family history was negative for sudden cardiac death or hypertrophic cardiomyopathy (HCM). Transthoracic echocardiography revealed asymmetric septal hypertrophy, systolic anterior motion of the mitral valve, dynamic LVOT obstruction (resting gradient 75 mmHg, 88 mmHg with Valsalva), hyperdynamic LV function, moderate left atrial enlargement, and mild–moderate mitral regurgitation. Laboratory workup revealed normal troponin, modestly elevated NT-proBNP (569 pg/mL), and normal pulmonary function testing. The initial diagnosis was HCM, and patient was referred for CMR.

Diagnostic Techniques and Their Most Important Findings: CMR demonstrated marked septal hypertrophy (25mm), near cavity obliteration during systole, preserved biventricular function (LVEF 63%), and systolic anterior motion of the mitral valve with moderate MR and a severely elevated LV mass index of 127 g/m2 (Figure 1A-D). Tissue characterization showed no late gadolinium enhancement (Figure 1E-F), normal myocardial native T1 (1245 ms on a 3T scanner), and normal ECV 25% (Figure 1G-H). The imaging findings were consistent with current diagnostic criteria for HCM. Molecular testing with the Invitae arrhythmia/cardiomyopathy panel identified a pathogenic GLA intronic variant (c.640-801G >A, IVS4+919G >A) and was negative for any HCM genes, confirming Fabry disease.

Learning Points from this Case: This case highlights an important diagnostic pitfall. Fabry cardiomyopathy is a recognized HCM phenocopy and is usually suggested by low native T1 times on CMR (1). However, in advanced Fabry disease, interstitial fibrosis may raise T1 values, resulting in pseudonormalization or even elevated T1 (2). In our patient, the combination of marked septal hypertrophy with normal T1/ECV and no LGE initially supported HCM, delaying suspicion of Fabry disease. Genetic testing ultimately established the diagnosis. The gene mutation identified is most commonly seen in Asian patients (3). Clinicians should be aware that Fabry disease can present with normal or borderline-high T1 times in advanced stages, underscoring the importance of correlating imaging with genetic evaluation. Early recognition is essential given the availability of enzyme replacement therapy and the potential for family screening.

Figure 1: SSFP Cine modified 5 chamber view end diastole (A), end systole (B), short axis basal slice end diastole (C), mid slice end diastole (D). LGE image short axis mid (E), two chamber (F). Pre T1 map mid (G) and post T1 map (H).