Table 2.

Sources of clinical and pharmacological heterogeneity in ET.

Feature	Comment
Head tremor	May be less responsive to medications than arm tremor (Song et al., 2008)
Voice tremor	May be less responsive to medications than arm tremor (Lyons and Pahwa, 2008a)
De novo vs. previously treated	Previously treated patients may be less responsive to medications, although no data directly address this issue
Short duration vs. long duration ET	Longer duration could be less responsive to medications, although no data directly address this issue