The blink reflex recovery cycle differs between essential and presumed psychogenic blepharospasm

Abstract

Background: Psychogenic blepharospasm is difficult to distinguish clinically from benign essential blepharospasm (BEB). The blink reflex recovery cycle measures the excitability of human brainstem interneurons and is abnormal in BEB. We wished to study the blink reflex recovery cycle in patients with atypical (presumed psychogenic) blepharospasm (AB).

Methods: This was a prospective data collection study investigating the R2 blink reflex recovery cycle at interstimulus intervals (ISI) of 200, 300, 500, 1,000, and 3,000 msec in 10 patients with BEB, 9 patients with AB, and 9 healthy controls. All patients had spasm of the orbicularis oculi muscles. To compare individual patients, an R2 recovery index was calculated as average of the recovery values at ISIs of 200, 300, and 500 msec, with the upper limit of normal defined as mean (control group) + 2 SD.

Results: The R2 recovery cycle was significantly disinhibited in patients with BEB, whereas patients with AB did not differ from controls on a group level. The upper limit of normal for the R2 recovery index was 61%. The R2 index was abnormal in 9 out of 10 patients with BEB and in none of the patients with AB.

Conclusions: A normal blink reflex recovery cycle indicates normal brainstem interneuron excitability. Assessment of the R2 recovery cycle may provide a useful diagnostic tool to distinguish patients with psychogenic blepharospasm from BEB and is worthy of further study.

Figure 1. Blink reflex recovery cycle

Blink reflex recovery cycle of the R2 component (area) in controls and patients with benign essential blepharospasm (BEB) and atypical (presumed psychogenic) blepharospasm (AB). Means are shown for the ratio of the conditioned R2 component to the unconditioned response. Error bars represent standard errors for the estimated least-squares means. *Significant difference between BEB vs controls and AB at a 5% level. X-axis: interstimulus intervals (ISI) in seconds. Y-axis: ratio of the conditioned to the unconditioned R2 response in percentage (%).

Figure 2. R2 recovery index in each subject

X-axis: groups: controls, AB = atypical (presumed psychogenic) blepharospasm; BEB = benign essential blepharospasm. Y-axis: R2 recovery index in percentage. The upper limit of normal for R2 area recovery index was 61% (light green area) (defined as the mean [dotted line] + 2 standard deviations [data from healthy controls]).