Comprehensive functional evaluation of the spectrum of multi-system atrophy with ¹⁸F-FDG PET/CT and ^99mTc TRODAT-1 SPECT: 5 years experience from a tertiary care center

Objectives: To elucidate the patterns of characteristic hypometabolism on ¹⁸F-FDG PET/CT in various subtypes of MSA and correlation with the patterns of uptake on Dopamine transporter imaging with ^99mTc TRODAT-1 SPECT.

Methods: A retrospective analysis of 61 patients of clinically suspected MSA was done. All the subjects underwent ^99mTc TRODAT-1 SPECT study and ¹⁸F-FDG PET/CT scan on two separate days, during the period of 2013-2018. The scans were analyzed both qualitatively (visually) and semi-quantitatively. The FDG uptake patterns were recorded and areas of hypometabolism that were two standard deviations from the mean were considered as abnormal.

Results: All the subjects had an abnormal pattern of FDG uptake on PET scan, both on visual inspection and semiquantitative analysis. In MSA-P subjects, diffuse predominant hypometabolism of the globus pallidus-putamen complex was noted with relative sparing of the caudate nuclei. In MSA-C subjects, characteristic hypometabolism was noted in cerebellum and brainstem. In mixed subtypes, variable involvement of the basal ganglia, cerebellum and brainstem was noted with fronto-parietal hypometabolism. TRODAT scan was abnormal in all and showed pronounced asymmetry. Rostro-caudal gradient was seen in the MSA-P subtype.

Conclusions: Dopamine transporter imaging agent ^99mTc TRODAT-1 SPECT not only helps in confirmation of Parkinsonian disorders, but also demonstrates varying patterns of distribution in different subtypes of MSA. Characteristic patterns of hypometabolism may help in differentiation of the subtypes of MSA in the presence of clinically overlapping symptoms.