Objective: To image progression of intestinal dysfunction, cardiac sympathetic denervation, and dopaminergic nigrostriatal damage in patients with isolated REM sleep behaviour disorder (iRBD).

Background: A majority of patients with iRBD convert to either Parkinson’s disease (PD), dementia with Lewy bodies, or multiple system atrophy within 15 years of diagnosis. Furthermore, iRBD patients have many symptoms similar to manifest PD patients including gastrointestinal dysfunction, orthostatic hypotension, and hyposmia. RBD patients display dysfunction of the sympathetic and parasympathetic nervous system, comparable to that seen in PD. However, progression rates of autonomic dysfunction in iRBD have not been studied with objective measures in detail, which is an aim of our ongoing study.

Method: Twenty-two iRBD patients were included at baseline and 14 participated in follow-up after 3 years. Gastrointestinal transit time (GITT) was examined using radio opaque markers, colonic volume was defined on abdominal CT scans, ¹²³I-MIBG scintigraphy was performed to measure function of cardiac sympathetic innervation, and ¹⁸F-DOPA PET measured nigrostriatal dopamine storage capacity. All examinations were performed at baseline and after 3 years.

Results: Patients displayed increased GITT (p=0.001), and colonic volume (p=0.01) at follow-up compared to baseline. GITT at follow-up had progressed in all patients but one and colonic volume increased in 11/14 RBD patients at follow-up compared to baseline. Furthermore, the 123I-MIBG uptake showed progressive reductions in 12/14 patients at follow-up (p<0.02) and the putaminal 18F-DOPA uptake showed progressive reductions in 10/14 patients (p=0.002) No correlations were seen between changes in intestinal or cardiac measurements and dopaminergic function.

Conclusion: Using objective markers, the present study documented that intestinal dysfunction shows marked deterioration in the majority of iRBD patients over a 3-year period. The absent correlation between these markers and nigrostriatal dopaminergic dysfunction suggests that progressive gastrointestinal dysfunction in iRBD is caused mainly by non-dopaminergic mechanisms. Furthermore, cardiac sympathetic degeneration was already severe in the majority of iRBD patients at baseline, but showed significant progression after three years.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/imaging-progressive-peripheral-and-central-dysfunction-in-isolated-rem-sleep-behaviour-disorder-after-3-years-of-follow-up/