Differentials
Parkinson disease
SIGNS / SYMPTOMS
Resting and action tremor, with rigidity, bradykinesia, and postural instability. Also, masked facies, cogwheeling, gait abnormalities, and occasionally early morning dystonia.[13]
INVESTIGATIONS
A dopaminergic agent (e.g., levodopa) trial can clarify the diagnosis. A dopamine transporter (DaT) scan may also be useful. Rest tremor is usually the predominant tremor type (4-6 Hz).
Dystonia
SIGNS / SYMPTOMS
Dystonic movements or postures, pain, a geste antagoniste (sensory trick), or muscular hypertrophy.
INVESTIGATIONS
If the clinical diagnosis is in doubt, genetic testing can help diagnose hereditary dystonia. Tremor physiology studies show co-contraction of agonist and antagonist muscle pairs.
Wilson disease
SIGNS / SYMPTOMS
Occurs in patients <40 years of age.
Characterized by resting and action tremor.
Other neurologic abnormalities present (e.g., dystonia, dysarthria, depression, cognitive impairment).[13]
INVESTIGATIONS
A low serum ceruloplasmin (<20 mg/dL) and a high 24-hour urine copper (>100 micrograms) indicates Wilson disease.[6]
Ophthalmologic examination with a slit lamp reveals Kayser-Fleischer rings in most patients who have neurologic signs.
Abnormal liver function might be present.
Enhanced physiologic tremor
SIGNS / SYMPTOMS
All normal, healthy individuals exhibit physiologic tremor.
It can be enhanced by intake of stimulants and other drugs, by withdrawal from drugs or alcohol, during certain medical conditions (elevated thyroid hormone levels or low glucose level), and by stress and fatigue.[6]
Enhanced physiologic tremor occurs in the absence of a neurologic disease and is high-frequency postural and kinetic tremor that occurs in the arms, legs, and voice, but not the head.
INVESTIGATIONS
A medication history looking for agents that cause enhanced physiologic tremor, and thyroid function tests screening for hyperthyroidism.
In some patients, quantitative computerized tremor analysis with accelerometers attached to the arms can help in diagnosing enhanced physiologic tremor.[77] Frequency shifts under inertial loading of the limbs or reduction of severity by stochastic noise may be observed.[78][79]
It is usually reversible once the cause is corrected.
Drug-induced tremor
SIGNS / SYMPTOMS
Occurs following ingestion of certain drugs (e.g., antipsychotics, lithium carbonate, theophylline valproic acid, cyclosporine, caffeine).
The tremor may affect the hands, arms, head, or other muscles, but rarely affects the legs or feet.
The shaking usually involves small, rapid movements, >5 times a second.
INVESTIGATIONS
The tremor will occur in a reasonable time frame following drug ingestion.
Psychogenic tremor
SIGNS / SYMPTOMS
There are several positive criteria to diagnose psychogenic tremor, such as sudden onset of tremor; an unusual combination of rest, postural, and kinetic tremor; variability of tremor direction, frequency, and amplitude; as well as distractibility and suggestibility.
INVESTIGATIONS
Entrainment is a useful tool. Psychogenic tremor either disappears or the tremor frequency in the affected body part shifts to match exactly the target frequency dictated by a metronome and produced by a rhythmic movement of the less-affected body part (e.g., the contralateral hand).
Orthostatic tremor
SIGNS / SYMPTOMS
Tremor in legs that occurs on standing, accompanied unsteadiness, tremor disappears on sitting or walking.
INVESTIGATIONS
Electromyography (EMG) of leg muscles (typically quadriceps) while standing, as a high-frequency peak on fast Fourier transform (FFT), usually between 12 Hz and 16 Hz.
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