Tremor has been documented by humans for thousands of years. Tremor is defined as an involuntary movement that is rhythmic (i.e., regularly repeated) and oscillatory (i.e., rotating around a central plane). Tremor can manifest in a myriad of different forms. As a result, the clinical phenomenology is very rich, and it is not surprising that there are many methods of classifying tremor.

Tremors are among the most common movement disorders. Diagnosis of these disorders is challenging. Approaching a patient with tremor requires a careful history and neurological examination focused on the clinical phenomenological nuances.

This type of action tremor occurs in both hands in virtually all people. The postural and kinematic components of this tremor are generally several Hertz faster in frequency than essential tremor, and the amplitude is generally lower than that of essential tremor, with the important caveat that at the onset of the disease patients with essential tremor have a low amplitude tremor that can be difficult to distinguish from enhanced physiologic tremor.

The history and physical examination are used first to determine whether the primary tremor is an action tremor (ie, postural, kinematic, or intention tremor) or a resting tremor. Indeed, the major distinction is between disorders in which action tremor is predominant and those in which resting tremor is predominant, each of which will be presented in turn, starting with the more diverse and more common type. This section discusses the most common disorders and those with distinct clinical features.

Primary writing tremor is a specific action tremor that occurs primarily or exclusively during writing and is absent or minimally involved in other movements or movements involving the hands.