(123)I-Labelled metaiodobenzylguanidine for the evaluation of cardiac sympathetic denervation in early stage amyloidosis

Cardiac amyloidosis is a rare disorder, but it may lead to potentially life-threatening restrictive cardiomyopathy. Cardiac manifestations frequently occur in primary amyloidosis (AL) and familial amyloidosis (ATTR), but are uncommon in secondary amyloidosis (AA). Echocardiography is the method of choice for assessing cardiac amyloidosis. Amyloid deposits impair the function of sympathetic nerve endings. Disturbance of myocardial sympathetic innervations may play an important role in the remodelling process. (123)I-MIBG can detect these innervation changes. Patients with biopsy-proven amyloidosis underwent general work-up, echocardiography and (123)I-MIBG scintigraphy. Left ventricular internal dimensions and wall thickness were measured, and highly refractile cardiac echoes (sparkling) were analysed. Early (15 min) and late (4 h) heart-to-mediastinum ratio (HMR) and wash-out rate were determined after administration of MIBG. Included in the study were 61 patients (30 women and 31 men; mean age 62 years; 39 AL, 11 AA, 11 ATTR). Echocardiographic parameters were not significantly different between the groups. Sparkling was present in 72 % of ATTR patients, in 54 % of AL patients and in 45 % of AA patients. Mean late HMR in all patients was 2.3 ± 0.75, and the mean wash-out rate was 8.6 ± 14 % (the latter not significantly different between the patient groups). Late HMR was significantly lower in patients with echocardiographic signs of amyloidosis than in patients without (2.0 ± 0.70 versus 2.8 ± 0.58, p < 0.001). Wash-out rates were significantly higher in these patients (-3.3 ± 9.9 % vs. 17 ± 10 %, p < 0.001). In ATTR patients without echocardiographic signs of amyloidosis, HMR was lower than in patients with the other types (2.0 ± 0.59 vs. 2.9 ± 0.50, p = 0.007). MIBG HMR is lower and wash-out rate is higher in patients with echocardiographic signs of amyloidosis. Also, (123)I-MIBG scintigraphy can detect cardiac denervation in ATTR patients before signs of amyloidosis are evident on echocardiography.