Early diagnosis of cardiac involvement in systemic sclerosis by 123I-MIBG neurotransmitter scintigraphy

Cardiac involvement of systemic sclerosis (SSc) is associated with a poor prognosis. Arrhythmias and conduction disturbances are a known feature of SSc. From histopathological examinations, it is known that the conducting system is secondarily involved as a result of focal fibrosis of the myocardium. Fibrotic changes are believed to be related to vasospasms, such as Raynaud's phenomenon. The sympathetic nervous system is very sensitive to ischaemia, impairing the energy-dependent uptake of intraneuronal norepinephrine. 123I-metaiodobenzylguanidine (123I-MIBG) is a metabolic analogue of norepinephrine and can therefore be used as a marker of norepinephrine depletion. The aim of the study was to evaluate the incidence and extent of SSc-associated ischaemic damage due to primary cardiac involvement by assessing intraneuronal 123I-MIBG uptake and distribution. Supplementary myocardial stress and rest perfusion scintigraphy, together with cardiological examinations (including an exercise stress test, Holter ECG and echocardiography), were performed in 18 patients. None of the patients showed evidence of ischaemia upon myocardial perfusion stress SPET or exercise stress. ECG at rest detected pathological conductance disturbances in one patient (6%). Holter ECG evoked pathological arrhythmias in three patients (17%). The echocardiograms of four patients (22%) showed a slight impairment of left ventricular diastolic function. 123I-MIBG scintigraphy revealed an inhomogeneous reduction of norepinephrine content in 15 patients (83%). It would appear that 123I-MIBG scintigraphy is able to detect cardiac SSc involvement prior to cardiological investigations.