Transcranial sonography in essential tremor

Essential tremor (ET) is the most common adult movement disorder. Especially in early stages the clinical differentiation between essential and Parkinsonian tremor may be a diagnostic challenge. Recent studies have consistently found hyperechogenic alterations in the area of the substantia nigra (SN) in patients with Parkinson's disease (PD) using transcranial sonography (TCS). The present chapter summarizes five studies, which have been performed to investigate SN echogenicity in patients with ET compared with PD patients and healthy control subjects and also includes our own experience. All of the studies published so far have shown that hyperechogenicity of the SN is a typical finding in about 90% of patients with PD, but not in patients with ET. In ET patients, the prevalence of hyperechogenicity is in the range of healthy control subjects or slightly above, which may indicate an increased risk for PD in the subgroup of ET patients with hyperechogenicity, consistent with the increased risk for PD that has been established in ET patient cohorts. As TCS is a noninvasive and inexpensive method, it seems to be a valuable instrument in the differentiation between ET and PD. Future follow-up studies on ET patients with SN hyperechogenicity will reveal whether those with increased echosignal are indeed the ones who may develop PD later in life.