A 40-year-old man comes to the office due to hand tremors for the past 2 months. The patient is an art teacher and has had difficulty demonstrating techniques in front of the class due to shaky hands. When noticing others looking at his hands, he becomes increasingly anxious and self-conscious, which tends to worsen the tremor. The patient has a history of bipolar disorder with a manic episode 6 months ago. He currently reports stable mood on the prescribed medication. The patient drinks alcohol occasionally and has not noticed any tremor changes with alcohol use. There is no family history of neurologic disorders. Vital signs are within normal limits. Physical examination shows fine, bilateral hand tremors that worsen with posture held against gravity. Muscle tone, strength, and deep tendon reflexes are normal throughout. Gait is normal. On mental status examination, he is cooperative and appears mildly anxious. The remainder of the physical examination shows no abnormalities. Which of the following is the most likely cause of this patient's current symptoms?
Tremor | Clinical features |
Essential |
|
Parkinson disease |
|
Cerebellar |
|
Physiologic |
|
This patient's fine action tremor of the hands that worsens with stress is consistent with physiologic tremor. Most individuals have a fine (ie, low-amplitude, high-frequency) tremor of the hands that usually goes unnoticed. However, the tremor may become visible when enhanced by increased sympathetic activity or certain medications. This patient's history of bipolar disorder suggests that his tremor is being enhanced by lithium.
Tremor is a common adverse effect of lithium, possibly due to increased iron accumulation in the substantia nigra. Lithium-induced enhanced physiologic tremor is typically symmetric, limited to the hands and upper limbs, and occurs when the medication is started or the dose is increased (eg, after a manic episode). It is nonprogressive and often decreases over time, even with no dosage reduction.
Lithium-enhanced physiologic tremor must be distinguished from tremor due to lithium toxicity, which typically causes an irregular, coarse tremor involving multiple parts of the body (not just the hands) accompanied by gastrointestinal or additional neurologic symptoms. Lithium toxicity requires treatment (eg, hydration, hemodialysis); in contrast, lithium-enhanced physiologic tremor is often managed with watchful waiting and modification of aggravating factors.
(Choice A) Lithium and other neuropsychiatric medications can cause dystonia. Dystonic tremors may present as irregular tremors exacerbated by stress. However, they occur with sustained muscle contractions (eg, wrist spasms, torticollis), typically in the same area as the tremor.
(Choice B) Essential tremor (ET) is also usually seen most prominently in the hands and can be worsened by anxiety or outstretched arms. However, it is predominantly an action tremor, so it becomes more pronounced at the end of goal-directed movements and improves with rest. Unlike this patient's tremor, ET classically improves with alcohol. In addition, patients are typically older or have a family history (ET is often autosomal dominant). Further, this patient's likely medication history makes a medication-enhanced physiologic tremor more likely.
(Choice C) Hyperthyroidism can cause an enhanced physiologic tremor indistinguishable from this patients' based on tremor characteristics. However, additional symptoms (eg, weight loss, heat intolerance) and findings of hyperthyroidism (eg, tachycardia, hypertension, hyperreflexia) are typically present.
(Choice D) In contrast to this patient, patients with Parkinson disease classically have a resting tremor that improves with intentional movement. In addition, tremor is accompanied by rigidity, bradykinesia, and gait disturbances.
Educational objective:
Certain medications (eg, lithium) can enhance a physiologic tremor, which is typically a fine, symmetric action tremor of the hands that increases with sympathetic activity.