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Reduced Myocardial 123-Iodine Metaiodobenzylguanidine Uptake: A Prognostic Marker in Familial Amyloid Polyneuropathy

Background— Transthyretin familial amyloid polyneuropathy is a hereditary form of amyloidosis characterized by sensorimotor and autonomic neuropathy, cardiac conduction defects, and infiltrative cardiomyopathy. Previous studies have suggested that myocardial sympathetic denervation assessed by 123-iodine metaiodobenzylguanidine (MIBG) imaging occurs early in disease progression. However, its prognostic significance was never evaluated. We aimed to study the long-term prognostic value of myocardial sympathetic denervation detected by MIBG imaging in transthyretin familial amyloid polyneuropathy. Methods and Results— A total of 143 individuals with V30M transthyretin mutation underwent Holter, ambulatory blood pressure monitoring, echocardiography, and MIBG imaging. Time to all-cause death was compared with late heart-to-mediastinum MIBG uptake ratio (H/M; either in relation to the estimated lower limit of normal [1.60] or as a continuous variable) using Cox proportional hazards regression. Multivariable analyses were performed to test the prognostic accuracy of clinical, neurological, and cardiovascular parameters. During a median follow-up of 5.5 years, 32 (22%) patients died. Five-year mortality rate was 42% for late H/M <1.60 and 7% for late H/M ≥1.60 (hazard ratio, 7.19; P<0.001). Late H/M was identified as an independent prognostic predictor. Fifty-three patients were submitted to liver transplantation. In comparison with neurophysiological score–matched controls, transplanted patients had lower long-term mortality (hazard ratio, 0.32; P=0.012). Patients with late H/M<1.60 were at higher risk of unfavorable outcome but seemed to have benefited from liver transplantation. Conclusions— Cardiac sympathetic denervation as assessed by MIBG imaging is a useful prognostic marker in transthyretin familial amyloid polyneuropathy.