Paired neurophysiological and clinical approach to brainstem assessment in Parkinson’s Disease

Question: Recent research has highlighted the role of brainstem (BS) structures in the early spread of Parkinson’s Disease (PD) pathological process. Vestibular Evoked Myogenic Potentials (VEMPs) corresponding to the Vestibulo-Ocular (VOR), Vestibulo-Masseteric (VMR) and Vestibulo-Collic (VCR) reflexes can provide information on BS function. Aims: to test the aforesaid set of VEMPs in a cohort of PD patients and healthy controls and to correlate it with presence of symptoms ascribable to BS dysfunction.
Methods: 19 PD patients (age 66.9±5.4 years; 12 males; mean disease duration 6.16±3.54 years) and 15 age and sex matched controls underwent bilateral recording of VOR, VMR and VCR from inferior oblique, masseter and sternocleidomastoid active muscles, respectively. PD patients were additionally administered a series of clinical scales used for evaluation of brainstem-integrated activities, namely sleep disorders (Epworth Sleepiness Scale, Parkinson’s Disease Sleep Scale and REM Sleep Behavior Disorder-Screening Questionnaire or RBD-SQ), postural instability (MiniBESTest) and depression (Geriatric Depression Scale). Groups’ comparisons were performed with χ2 test and Mann-Whitney U-test; Sperman’s rho test was used for correlation analysis.
Results: VEMPs were significantly impaired in patients compared to controls, absence being the main pattern of alteration. When the set of the 3-VEMP battery was analyzed, both number of altered reflexes (p=0.017) and severity of alteration (p=0.001) were significantly higher in patients than controls. As for each single VEMP, only the VOR and the VMR were significantly altered (VOR: p=0.022; VMR: p=0.005; VCR: p=0.056). Clinical scales revealed the presence of some degree of depression in 36.8% of patients, sleep disturbances in 68.4%, REM sleep disorder in 26.3% and postural instability in 36.8% of PD patients. A significant correlation with VEMP alterations was found only for high scores on RBD-SQ (ρ=0.554; p=0.014).
Conclusions: Combined assessment of VOR, VMR and VCR was able to detect BS dysfunction in a rostro-caudal extension in PD. This may prove interesting in the perspective of identifying neurophysiological markers of BS dysfunction in early stages of the disease.