A 65-year-old man presents to his primary care provider with bilateral tremor in his upper extremities that has worsened gradually over the past several months. The tremor is slightly worse on the left side and more pronounced near his hand. The tremor embarrasses the patient, and he feels that his coworkers have begun to question his ability to perform required tasks. These situations make him nervous, which makes his tremor worse. His father had Parkinson's disease (PD), and the patient is worried that he is also developing the condition.
Many practitioners feel unprepared to deal with a patient like this one, which means that patients who present with tremor often are inadequately treated or referred quickly to a neurologist. Knowing a few basic concepts, however, can help clinicians to assess tremor symptoms quickly and maximize therapy, as well as to recognize when additional interventions are needed.
Differentiating pathologic forms of tremor
Although pathologic tremors can be readily observed, the challenge is determining the etiology and the most 
effective treatment. More than 10 distinct types of tremor, with varying patterns of onset and degrees of progression, have been identified.1 Although their characteristics have been documented, the underlying disease mechanisms are not well understood, leading to disagreement about how particular tremors are categorized and treated. Another complicating factor can be multiple kinds of tremor in the same patient.
All patients have physiologic tremor, or rhythmic oscillatory movements of a body part with a relatively constant frequency and variable amplitude.1 Most people are unaware of these tremors, which are not usually visible to the naked eye. However, several factors can exacerbate inherent tremors to the point of dysfunction. Most of these factors increase sympathetic activity; they include medications, toxins, and physiologic or emotional states (see Table 1).2,3 While enhancement of normal physiologic tremor is most common, several pathologic forms can also occur and can be helpfully characterized as either resting or action tremors.
Resting tremor occurs when the affected body part is relaxed, stationary, and completely supported by gravity; it lessens or disappears with active motion. Since resting tremor does not affect voluntary activity, it does not usually limit a patient's ability to function, although it can lead to embarrassment by complicating motor activities that involve pauses, such as using utensils or handwriting.4,5 PD is the most common cause of resting tremor (see “Differentiating types of tremor”).
Action tremor, by contrast, occurs with muscle contraction and is further divided into postural, isometric, and kinetic forms. Postural tremor occurs when the affected body part maintains its position against gravity. Isometric tremor occurs with muscle contraction against stationary objects. Kinetic tremor is associated with movement and can be subdivided into simple tremor, which occurs with any movement, and intention tremor, which occurs with goal-directed movements. With the latter, the tremor typically increases as the hand moves closer to its goal; this contrasts with postural and isometric tremors, which either are constant throughout the range of motion or increase after the affected extremity reaches its goal.
Although these classifications are helpful, several types of tremor do not easily fit into these categories. For example, some postural tremors can continue when the limb is supported, thus making the distinction between postural and resting tremor difficult.5
History and physical examination
A careful history and a review of systems are crucial for accurate diagnosis and subsequent treatment. This 
approach should include a detailed characterization of the tremor itself and a thorough family and social history, including all medications and drug or alcohol use. The practitioner must also consider any underlying medical conditions that can influence tremor manifestation.
Along with the history, the practitioner uses clinical judgment and observation of the tremor to make a diagnosis. The key variables include the degree of symmetry, rhythmicity (regular or irregular oscillations), location (distal or proximal), amplitude (degree of limb displacement with involuntary muscle contraction), and frequency (number of oscillations per second).6 Though precise determinations of these variables can be determined only electrophysiologically, rough estimates can greatly facilitate tremor diagnosis. For example, frequency can be characterized as slow (2-5 Hz), intermediate (5-10 Hz), or fast (10-18 Hz). Amplitude can similarly be described as fine, medium, or coarse, depending on the degree of displacement produced by the tremor.7