The glabellar reflex is a poor measure of Parkinson motor severity

The glabellar reflex (GR) is often interpreted as a clinical measure of parkinsonism, although data to support this are weak. It is one of ten items used in the Simpson Angus Scale, a popular measure of parkinsonism in psychiatric studies of neuroleptic drugs. We hypothesized that the GR might be a measure of hypomimia.

This was a chart review of 99 consecutive patients with idiopathic Parkinson's disease (PD) seen in a movement disorders center. All patients had standard Unified Parkinson's Disease Rating Scale (UPDRS) motor scale assessments in addition to a standardized assessment of the glabellar reflex (GR). We compared the number of blinks to the hypomimia score (item 2 on UPDRS motor scale) and other measures of PD severity.

We found that there was a statistically significant but weak correlation between the GR blink number and hypomimia as well as the total score on the UPDRS motor section. We also found that the blink number was widely discrepant for an individual hypomimia score.

The GR is not a useful measure of hypomimia or motor severity in PD.