Antimyosin Scintigraphy for Detection of Cardiac Amyloidosis

C amyloidosis belongs to the list of important cardiac masqueraders; it is one of the more likely causes of restrictive cardiomyopathy, the diagnosis of which may be frequently missed.1 Infiltration of the heart muscle by amyloid is frequently found in patients with amyloidosis and is associated with very poor prognosis.2 Echocardiography and radionuclide imaging with techetium-99m pyrophosphate or iodine-123 labeled serum amyloid P component offer valuable insight to the diagnosis of cardiac amyloidosis, but for a definitive diagnosis of this condition an endomyocardial biopsy is usually required.3–5 We have recently reported a case of cardiac amyloidosis detected by indium-111 antimyosin imaging.6 In this study we prospectively investigated the diagnostic value of antimyosin scanning in a group of patients with biopsy-proven cardiac amyloidosis; this study highlights a new, noninvasive method for diagnosing cardiac amyloid deposits. • • • Seven patients with histologically confirmed primary or myeloma-related amyloidosis were studied; 3 were women and 4 men and their mean age was 56 6 9 years (range 37 to 61). Characteristics of the patients are shown in Table I. Clinically overt heart failure was present in 4 patients and all patients had left ventricular thickening on the echocardiogram and an abnormal electrocardiogram. Right ventricular endomyocardial biopsy was performed in all patients and it was successful in 6 of 7 patients; Congo red staining was positive for amyloid in the vascular wall and interstitium of all specimens. In 1 patient (patient 2), biopsy was not obtained because the patient developed ventricular tachycardia during the catheterization. However, in this patient the diagnosis of cardiac amyloidosis was confirmed by the presence of left ventricular thickening on the echocardiogram, a low voltage on the electrocardiogram, and presence of amyloid in a kidney biopsy specimen. Six patients with low probability of cardiac amyloidosis formed a control group; there were 2 women and 4 men with a mean age of 54 6 11 years (range 34 to 60). All control patients had a long-standing history of systemic hypertension and left ventricular hypertrophy on the echocardiogram (septum 1.5 6 0.4 mm, posterior wall 1.4 6 0.3 mm), but no evidence of plasma cell dyscrasia. An additional control group consisted of 10 patients with long-standing (.1 year) history of idiopathic-dilated cardiomyopathy and no evidence of myocarditis on endomyocardial biopsy; there were 4 women and 6 men and the mean age was 49 6 6 years (range 38 to 57). Left ventricular ejection fraction was 23 6 13% (range 9 to 49). All patients underwent myosin-specific monoclonal antibody imaging. Antimyosin antibody (Myoscint, Centocor, Inc., Leiden, The Netherlands) was supplied as a sterile nonpyrogenic solution containing 0.5 mg of R11 D10 Fab diethylenetramine pentaacetic acid, which is a mouse monoclonal antibody fragment that binds specifically to myosin. The antimyosin was radiolabeled by the addition of sterile indium-111 chloride. Two millicuries of indium-111 were diluted to 10 ml of volume and were administered intravenously by slow injection. Planar imaging was performed after 48 hours using a gamma camera (General Electric Maxi Camera 400, Milwaukee, Wisconsin). Three views were obtained (anterior, 45° left anterior oblique, and left anterior oblique, 70°) using a 128 3 128 matrix for 10 min/view. Both photopeaks of indium-111 were used (173 keV and 247 keV) with 20% energy windows. A heart-to-lung (H/L) ratio was used to quantify tracer uptake; the unprocessed anterior projection was used to adjust a region of interest in the myocardium and a region of interest in each lung. The average count per pixel in the myocardium was divided by the average count per pixel in each lung to obtain the H/L ratio. A ratio .1.6 was considered abnormal.7 The antimyosin antibody was administered without adverse reactions in all patients and control subjects. In the control group, all 6 patients had a normal antimyosin study; H/L ratio ranged from 1.3 to 1.6 (mean 1.43 6 0.1). In each patient with cardiac amyloidosis the antimyosin scanning was always abnormal (Figure 1); the H/L ratio ranged from 2.1 to 3.2 (mean 2.5 6 0.4) and was significantly higher than that observed in the control group (p ,0.001). Diffuse uptake of antimyosin was observed in all patients with cardiac amyloidosis. Patients with amyloidosis and congestive heart failure had a higher H/L ratio (2.76 6 0.30) compared with patients without clinically evident heart failure (2.17 6 0.06, p 5 0.04). The H/L ratio in the group of patients with idiopathic-dilated cardiomyopathy was 1.6 6 0.2 (range 1.4 to 2.1) and was significantly lower than that observed in amyloidosis patients (p ,0.001); the H/L ratio was abnormal in 4 of these patients. From the Department of Clinical Therapeutics and Department of Nuclear Medicine, Alexandra University Hospital, Athens, Greece. Dr. Lekakis’ address is: 86 Alkionis Street, P. Faliron 175 62, Athens, Greece. Manuscript received March 11, 1997; revised manuscript received and accepted June 2, 1997.