Researchers have found that imaging contrast agent MIBG can help detect early nerve cell damage affecting the heart before serious tissue damage and cardiac impairment in patients with familial amyloid polyneuropathy (FAP). The agent may have early diagnostic value for these patients.
This finding was reported in a study published in the European Journal of Nuclear Medicine and Molecular Imaging.
FAP is a genetic disease characterized by the accumulation of amyloid aggregates. These mainly affect peripheral nerve cells, but as disease progresses, they can accumulate in organs in the body, including the eyes, kidneys, and heart. The amyloid aggregates will cause nerve cell damage and also prevent the normal function of the affected tissues.
Cardiac problems caused by the accumulation of amyloid fibers in the heart are the main cause of death among FAP patients. Diagnosis of cardiac amyloidosis relies on tissue biopsy or the associative evidence of positive FAP diagnosis and heart dysfunction. Currently, there is no sensitive, noninvasive method that can be used to specifically detect this serious heart condition.
In the study, “Cardiac denervation evidenced by MIBG occurs earlier than amyloid deposits detection by diphosphonate scintigraphy in TTR mutation carriers,” a French team tested the potential of two imaging contrast agents to diagnose heart involvement in FAP patients.
The study included 75 patients with confirmed FAP who underwent imaging evaluation for cardiac involvement at the French Reference Center for Amyloidosis (CRMR-NNERF). The team used 123I-MIBG and 99mTc-diphosphonates (DPD) to specifically detect nerve cell damage and the presence of amyloid fibers in the heart, respectively.
The imaging analysis revealed that 65% of the participants had nerve cell damage and 39% had myocardial DPD uptake, suggesting the presence of amyloid fibers. All but two patients who had normal MIBG also had normal DPD uptake.
Those with normal MIBG showed little or no signs of cardiac amyloidosis, whereas patients with positive DPD had significant evidence of biological and functional cardiac dysfunction.
Among the 31 asymptomatic FAP patients, MIBG was found to be abnormal in 15 (48%) and DPD was abnormal in in eight. All asymptomatic patients with normal MIBG had normal DPD values. These findings suggest that denervation occurs earlier than amyloid deposition in the heart.
Collectively, these results showed MIBG and DPD imaging are complementary noninvasive methods that “allow for diagnosis and evaluation of cardiac involvement in hereditary TTR amyloidosis,” the researchers wrote.
In addition, MIBG shows promise as an early diagnostic tool, since a mild decrease in MIBG uptake is “associated with very early signs” of cardiac involvement, “including in the subgroup of asymptomatic carriers,” the researchers added.