What is the functional significance of nondominant arm tremor in essential tremor?

Tremor in the dominant arm is often the focus of clinical attention in essential tremor (ET) yet many daily activities require both arms. The functional relevance of nondominant arm tremor has rarely been studied. In 181 right-handed patients with ET, action tremor in each arm was rated using a clinical rating scale. Tremor disability was self-reported and a performance-based test of function was administered. Independently of tremor on the right, greater tremor severity on the left was associated with greater self-reported disability (P = 0.02) and greater performance-based dysfunction (P < 0.001). In 5.0% of patients, tremor was largely restricted to the nondominant arm. Nondominant arm tremor, independent of dominant arm tremor, had a significant functional correlate, contributing to both greater perceived and greater observable functional difficulty. In 5% of patients, tremor in the nondominant arm was the likely motivator for seeking care, which is another indication of its functional significance.