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.