BACKGROUND: Rapid eye movement (REM) sleep behaviour disorder (RBD) is a parasomnia characterised by the loss of REM sleep muscle atonia and the enactment of dreams. Acute RBD associated with alcohol withdrawal syndrome is known, but the studies are limited, particularly on its neurobiological underpinnings and management alongside the withdrawal state. This work attempts to address this using a case study and relevant literature review.
METHODS: A 40-year-old male with alcohol dependence (for 20 years) reported new-onset terrifying nightmares and violent behaviours in his sleep precipitated by alcohol withdrawal states for the last 18 months. The polysomnographic finding of REM-without-atonia supported the diagnosis of RBD. He was treated with chlordiazepoxide 100 mg/day (gradually tapered and stopped) and thiamine supplements. Post-discharge, he remained abstinent and symptom-free during the three months of follow-up.
CONCLUSIONS: RBD related to alcohol withdrawal syndrome has been previously described in a few anecdotal reports. Sudden withdrawal from central nervous system suppressants like alcohol is hypothesised to cause a homeostatic imbalance in gamma-aminobutyric acid (GABA) pathways and \'REM rebound\', resulting in the clinical and polysomnographic picture of RBD. Benzodiazepines have been found to be useful in both RBD and alcohol withdrawal.
CONCLUSIONS: Alcohol withdrawal syndrome may present with acute RBD, which can be treated with a short course of benzodiazepine. However, further studies are needed to explore the long-term course of RBD in these patients.

Parkinson\'s disease is characterized by the presence of abnormal, intraneuronal α-synuclein aggregates, which may propagate from cell-to-cell in a prion-like manner. However, it remains uncertain where the initial α-synuclein aggregates originate. We have hypothesized that Parkinson\'s disease comprises two subtypes. A brain-first (top-down) type, where α-synuclein pathology initially arises in the brain with secondary spreading to the peripheral autonomic nervous system; and a body-first (bottom-up) type, where the pathology originates in the enteric or peripheral autonomic nervous system and then spreads to the brain. We also hypothesized that isolated REM sleep behaviour disorder (iRBD) is a prodromal phenotype for the body-first type. Using multimodal imaging, we tested the hypothesis by quantifying neuronal dysfunction in structures corresponding to Braak stages I, II and III involvement in three distinct patient groups. We included 37 consecutive de novo patients with Parkinson\'s disease into this case-control PET study. Patients with Parkinson\'s disease were divided into 24 RBD-negative (PDRBD-) and 13 RBD-positive cases (PDRBD+) and a comparator group of 22 iRBD patients. We used 11C-donepezil PET/CT to assess cholinergic (parasympathetic) innervation, 123I-metaiodobenzylguanidine (MIBG) scintigraphy to measure cardiac sympathetic innervation, neuromelanin-sensitive MRI to measure the integrity of locus coeruleus pigmented neurons, and 18F-dihydroxyphenylalanine (FDOPA) PET to assess putaminal dopamine storage capacity. Colon volume and transit times were assessed with CT scans and radiopaque markers. Imaging data from the three groups were interrogated with ANOVA and Kruskal-Wallis tests corrected for multiple comparisons. The PDRBD- and PDRBD+ groups showed similar marked reductions in putaminal FDOPA-specific uptake, whereas two-thirds of iRBD patients had normal scans (P < 10-13, ANOVA). When compared to the PDRBD- patients, the PDRBD+ and iRBD patients showed reduced mean MIBG heart:mediastinum ratios (P < 10-5, ANOVA) and colon 11C-donepezil standard uptake values (P = 0.008, ANOVA). The PDRBD+ group trended towards a reduced mean MRI locus coeruleus: pons ratio compared to PDRBD- (P = 0.07, t-test). In comparison to the other groups, the PDRBD+ group also had enlarged colon volumes (P < 0.001, ANOVA) and delayed colonic transit times (P = 0.01, Kruskal-Wallis). The combined iRBD and PDRBD+ patient data were compatible with a body-first trajectory, characterized by initial loss of cardiac MIBG signal and 11C-colonic donepezil signal followed by loss of putaminal FDOPA uptake. In contrast, the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal. These findings support the existence of brain-first and body-first subtypes of Parkinson\'s disease.