An Unusual Case of Transthyretin Cardiac Amyloidosis Presenting as Heart Failure With Improved Ejection Fraction Without Left Ventricular Hypertrophy

Heart failure with preserved ejection fraction (EF) and left ventricular (LV) hypertrophy (LVH) are typical phenotypes of transthyretin cardiac amyloidosis (ATTR-CA). Extracardiac manifestations, such as carpal tunnel syndrome, lumbar spinal stenosis, or biceps tendon rupture, frequently precede the development of overt cardiac involvement. We report a rare case of ATTR-CA presenting as heart failure with improved EF (HFimpEF) without LVH in an elderly patient, where the diagnosis was prompted by bilateral carpal tunnel syndrome, lumbar spinal canal stenosis, and persistently elevated troponin levels. An 88-year-old man presented with a two-week history of fatigue and anorexia. He had lumbar spinal canal stenosis and thenar muscle atrophy in both hands, suggestive of bilateral carpal tunnel syndrome. An electrocardiogram revealed right bundle branch block and left axis deviation, without low voltage or a pseudo-infarct pattern. An echocardiogram showed a reduced EF of 35% without LVH, with an LV end-diastolic diameter of 50 mm. Coronary angiography revealed no significant stenosis. He was diagnosed with non-ischemic heart failure with reduced EF. The presence of extracardiac red flags and elevated troponin levels raised suspicion for cardiac amyloidosis. 99m-Technetium pyrophosphate scintigraphy demonstrated Perugini grade 2 myocardial uptake (moderate uptake equal to rib uptake) on both planar and single photon emission tomographic images at the three-hour mark. No monoclonal protein was detected, and the free light chain ratio (kappa to lambda) was 1.54, within the normal range, leading to a non-invasive diagnosis of ATTR-CA. After 12 weeks of conventional heart failure therapy, follow-up echocardiography revealed an improved EF of 55% and a decrease in LV end-diastolic diameter to 35 mm, confirming the diagnosis of HFimpEF and indicating LV reverse remodeling and optimized volume status. In conclusion, this case illustrates that ATTR-CA can present atypically as HFimpEF, even in the absence of LVH or typical cardiac red flags. It highlights the importance of recognizing extracardiac signs and considering ATTR-CA in patients who do not exhibit typical features of LVH or traditional heart failure phenotypes.