Blink reflex recovery cycle in patients with essential tremor associated with resting tremor

An increased R2 recovery component of the blink reflex (R2-BRrc) has been commonly observed in Parkinson disease, cranio-cervical dystonia, and dystonic tremor, while the BRrc was reported normal in patients with essential tremor (ET). We studied BRrc in patients with ET associated with resting tremor (rET) in comparison with patients with ET.

This was a cross-sectional study investigating R2-BRrc at interstimulus intervals (ISI) of 100, 150, 200, 300, 400, 500, and 750 msec in 14 patients with rET, 14 patients with ET, and 16 healthy controls. To compare individual patients, we calculated an R2 recovery index in each subject as the mean of R2 area ratio values at ISIs of 150, 200, 300, 400, and 500 msec. All patients and controls underwent DAT-SPECT.

Patients with rET differed from those with ET for the presence of resting tremor associated in several cases (36%) with a subtle arm dystonia. DAT-SPECT was normal in all patients and controls. All patients with rET (with and without dystonia) had an increased R2-BRrc while all patients with ET had a normal BRrc comparable to that of control subjects. The R2 recovery index was abnormal in all patients with rET but in none of the patients with ET.

Patients with rET showed increased R2-BRrc, suggesting that this form of tremor may be a dystonic tremor rather than a subtype of ET. BRrc helps to correctly diagnose DAT-negative patients with resting tremor also in the absence of overt dystonic posturing.