False-positive bone scintigraphy denoting transthyretin amyloid in elderly hypertrophic cardiomyopathy

A positive nuclear scintigraphy with hydroxy bisphosphonate bone tracer (99mTc-HPD) is believed to have high sensitivity (>99%) and specificity (91%) for the diagnosis of transthyretin amyloid cardiomyopathy. We report the case of an 85-year-old man with increased thickness of ventricular walls and a positive bone scintigraphy, who was unexpectedly found to have sarcomeric hypertrophic cardiomyopathy at left ventricular endomyocardial biopsy. Congo Red staining, immunohistochemistry, and transmission electronmicroscopy on six left ventricular samples scored negative for amyloidosis but were suggestive for sarcomeric hypertrophic cardiomyopathy. Genetic study did not show TTR and most commonly involved sarcomeric genes mutations. In hypertrophic cardiomyopathy focal cell necrosis related to demand/supply oxygen mismatch, small vessels disease or inflammation could be responsible of a false-positive bone scintigraphy signal for transthyretin amyloidosis. Because of this, especially in view of a possible specific treatment, endomyocardial biopsy is highly recommended for the correct diagnosis of cardiomyopathies with hypertrophic phenotype.