P326 FALSE POSITIVE BONE–SCINTIGRAPHY IN ELDERLY HYPERTROPHIC CARDIOMYOPATHY

Abstract

Abstract Differential diagnosis of cardiomyopathies with hypertrophic phenotype is crucial because some secondary forms of cardiac hypertrophy can be susceptible of specific treatment aimed to revert and/or stabilize the increase in wall thickness.A positive nuclear scintigraphy with hydroxy bisphosphonate bone tracer (99mTc–HPD)is believed to have high sensitivity and specificity for the diagnosis of transthyretin (TTR) amyloid cardiomyopathy. An 85–year–old man with systemic arterial hypertension was admitted because of pre–syncope associated to evidence at Holter monitoring of both bradiarrhythmias(1st degree AV block with PR interval of 300 ms and several episodes of 2nd degree Mobitz type 1 AV block with electrical pause >3 s) and tachyarrhythmias.He suffered from a bilateral carpal tunnel syndrome that underwent surgery 2 years earlier.Routine laboratory tests were normal except for elevated cardiac troponin HS(0.295 mcg/L,nv < 0.014 mcg/L) and N–terminal pro–BNP (384.3 pg/mL,nv = 0–254 pg/mL).Because of clinical suspicion of senile amyloidosis,nuclear scintigraphy with hydroxy bisphosphonate bone tracer(99mTc–HPD)was performed,that revealed a grade 3 myocardial uptake.Serum–urine immunofixation and immunoglobulin free light–chain was negative for monoclonal gammopathy.Neurological examination was unremarkable Genetic test did not show TTR mutation.Thus,a diagnosis of wild–type TTR cardiac amyloidosis was suggested.The patient,in view of Tafamidis treatment,underwent a LV endomyocardial biopsy.Six specimens were drawn from the LV,cut and processed for histology,immunohistochemistry,and transmission electron microscopy. Unexpectedly,histology failed to confirm amyloid deposition but revealed the presence of severely hypertrophied disarrayed cardiomyocytes fragmented in short runs by interstitial and replacement fibrosis,denoting a sarcomeric hypertrophic cardiomyopathy.Congo red staining at polarized light scored negative for areas of apple–green florescence.Immunohistochemistry form transthyretin,kappa/lambda light chain and SAA was negative.Transmission electron microscopy failed to demonstrate the presence of rigid unbranched amyloid fibrils.Thus,a final diagnosis of hypertrophic cardiomyopathy was reached. Coclusion:A positive cardiac signal of bone scintigraphy can occur in other pathologic settings.Future studies are needed to investigate the incidence of false–positive TTR cardiac amyloidosis to bone scintigraphy compared with endomyocardial biopsy.