Case history. An 84-year-old man with systemic hypertension had papillary carcinoma of the thyroid and lymph node metastases that were treated with thyroidectomy. He also had atrial fibrillation with a slow ventricular response (minimum heart rate on 24-hour Holter monitoring of 42 beats/min) and left bundle branch block. The patient had a good exercise tolerance (600 yd on flat ground), with no cardiac symptoms. The results of his examination were otherwise unremarkable. Transthoracic echocardiogram showed a normal left ventricular size but a dilated left atrium, with mild mitral, aortic, and tricuspid regurgitation. Technetium 99m sestamibi myocardial perfusion scintigraphy after 1 month of echocardiography (Figure 1) showed no evidence of ischemia but an ejection fraction of 28% (Figure 2), suggesting the possibility of primary or secondary muscle disorder. A VVIR pacemaker was inserted, and thyroxine administration was started. While receiving thyroxine, the patient had residual papillary thyroid carcinoma and pulmonary metastases developed. Twelve months after thyroidectomy, fluid overload and pulmonary congestion developed, and he started taking furosemide, with resolution of symptoms to New York Heart Association class II. Eighteen months after thyroidectomy, lower back pain developed, and a Tc-99m methylene diphosphonate bone scan showed no bone metastases, but there was unusually high and homogeneous myocardial uptake of Tc-99mMDP, suggesting an infiltrative disease, possibly amyloidosis (Figure 3). Repeat echocardiography showed features suggestive of cardiac amyloidosis (Figure 4), with increased septal thickness (2.8 cm) relative to the posterior wall (1.9 cm), reduced left ventricular systolic function, a dilated left atrium (5.0 cm) with no evidence of organic mitral valve disease, and a biventricular restrictive filling pattern. The electrocardiogram at that time showed a low-voltage pattern. The patient’s condition deteriorated, and he died 2 months later at home. Postmortem examination was not performed. Discussion. This case illustrates presumed cardiac amyloidosis diagnosed incidentally by bone scan. Bone scintigraphy does not show appreciable uptake of tracer in the normal heart. Myocardial uptake of the Tc-99m– labeled bone-seeking agents was shown in the 1980s to be suggestive of cardiac amyloidosis. However, endomyocardial biopsy remains the standard for the diagnosis of myocardial amyloidosis. In a prospective study of endomyocardial biopsy–proven amyloidosis, only 1 of 5 patients had intense uptake. The authors concluded that uptake of the bone agent (pyrophosphate in their study) by the myocardium makes the diagnosis of amyloidosis highly likely but is not sufficiently sensitive to warrant routine screening of patients. In a separate study of patients with 5 different types of amyloidosis with bone scans, echocardiography was shown to be more sensitive than bone scintigraphy in the diagnosis of cardiac amyloidosis. Further uptake of bone agent in the myocardium has also been described in a patient with chronic renal failure undergoing hemodialysis and severe hyperparathyroidism. This was associated with other features of hyperparathyroidism on bone scan such as lytic bone lesion as a result of a brown tumor and diffuse extraskeletal uptake in the lungs, kidneys, and femoral arteries. This was reported to partially regress after 4 years of parathyroidectomy. Isolated uptake of bone agent in the heart would have high specificity for suspecting amyloidosis, but bone scintigraphy is not the most sensitive method for detecting cardiac amyloidosis. This would depend on the affinity of calcium for the bone agent between different types on amyloid fibrils. From the Royal Brompton Hospital, National Heart and Lung Institute, Imperial College London, and Royal Marsden Hospital, London, England. Reprint requests: Kshama Wechalekar, MBBS, DRM, DNB, Department of Nuclear Medicine, Royal Brompton Hospital, Sydney Street, London SW3 6NP, England; K.Wechalekar@rbht.nhs.uk. J Nucl Cardiol 2007;14:750-3. 1071-3581/$32.00 Copyright © 2007 by the American Society of Nuclear Cardiology. doi:10.1016/j.nuclcard.2007.07.002
Read full abstract