Perverted Head-Shaking and Positional Downbeat Nystagmus in Essential Tremor.

Even though the pathophysiology is not completely understood, cerebellar dysfunction has been invoked in essential tremor (ET). We evaluated cerebellar dysfunction in ET with the presence of perverted head-shaking (pHSN) and positional downbeat nystagmus (pDBN) which are known to reflect cerebellar dysfunction. First, we reviewed the videooculography (VOG) of 185 patients with ET from March 2007 to April 2010. Seventeen of 28 patients with pHSN and pDBN were followed up for at least a 1.8-year interval from baseline to determine the clinical course. And then, we recruited 52 consecutive patients with ET and compared their ocular motor findings with 51 normal controls using VOG. Among the 185 patients with ET, 28 (15.1 %) showed pHSN (n = 23, 12.4 %) or pDBN (n = 8, 4.3 %). Seventeen of them who were followed up did not develop Parkinsonism or other neurologic deficits during the observation period. The subsequent case-control study showed a higher prevalence of pHSN or pDBN (11/52, 21.2 %, pHSN in nine and pDBN in five) in patients with ET than in the normal controls (2/51, 3.9 %, pHSN only, P = 0.015). The tremor rating scale or involved body sites did not differ between the patients with and without pHSN/pDBN. pHSN and pDBN were more common in patients with ET than in the normal controls. This result supports that cerebellar dysfunction is associated with ET.