Postural Instability in Idiopathic Parkinson's Disease: Determination of VEP, BAER, and SSEP Cutoff Values for an Early Screening of Fall.

BACKGROUNDS AND AIMS: Idiopathic Parkinson's disease (IPD) patients had progressively increased slowness, rest tremors, rigidity, and postural instability (PI). Postural stability depends on sensory inputs from visual, auditory, and somatosensory modalities. We tried to find important cutoff values of visual evoked potential (VEP), brainstem auditory evoked response (BAER), and short-latency somatosensory evoked potentials (SSEP) for determining postural stability in IPD patients.

METHODOLOGY: About 50 IPD patients were recruited in a cross-sectional observational study. A pull test was used to determine postural stability. Patients were subgrouped into tremor dominant (TD variant) (n = 37) and PI and gait disorder (PIGD) (n = 13). We generated receiver operating characteristic (ROC) curves to classify patients into posturally stable and unstable and measured VEP, BAER, and SSEP cutoff values. The area under the curve (AUC) >0.8 was taken as significant.

RESULTS

Significant VEP N75, P100, and N145 cutoff values were noted bilaterally in IPD and its subgroups (TD and PIGD). Except for wave I, the latency of all other BAER waves showed significant cutoff values bilaterally in IPD and subgroups (TD and PIGD). Most BAER cutoff values in the IPD and TD subgroups reached 100% specificity. No significant SSEP values were noted.

DISCUSSION: Many significant VEP and BAER parameters with good sensitivity and specificity would guide clinicians in predicting PI and falls in IPD. The TD had lower BAER latency cutoff values than the PIGD. The postural stability of the TD subgroup was more dependent on the vestibular sensory input than that of the PIGD subgroup. Less vestibular compensatory support in PIGD led to a more severe phenotype than in TD.

CONCLUSION

We found many evoked potential significant cutoff values determining postural stability in IPD and its subgroups (TD and PIGD). Lesser vestibular compensatory support in PIGD led to a more severe phenotype than in TD.