Drug-induced Movement Disorders

Diagnosis

The differential diagnosis of a DIMD is the same as that for the movement disorder that is not drug induced. The diagnosis of DIMD is a two-step process: the first entails the recognition of the abnormal movement and, the second, the identification of the temporal relationship between institution of therapy with a DRBD (acute) or exposure to a DRBD within the previous three months (tardive) and the abnormal movement. DIMDs manifest identically to other movement disorders that are not caused by drugs. For example, tremor looks like tremor and dystonia looks like dystonia, independent of the etiology. However, with DIMD, a few clues may assist the clinician in correctly identifying the cause of the movement. The etiology is more likely to be drug induced when the patient has

• Both hypokinetic and hyperkinetic movements occurring simultaneously
• Axial dystonia, particularly when it occurs in conjunction with a hyperkinetic movement
• A sudden onset of parkinsonism

Obtaining a detailed history of any medication use in the previous three months is important in delineating the cause of DIMD (Table 1). Inquiries specifically about any anesthesia exposure during surgical procedures that the patient may have undergone, antinausea treatments, and use of weight-reduction, adrenergic agents, or antidepressant medications may aid in identifying often-overlooked causes of DIMD.

Table 1—Abnormal involuntary movements and the drugs that may cause them

Drug category	Examples	Movement	Commonness of occurrence
Antidepressant
Tricyclic		Tremor, OBLFD, gait ataxiaa	+
SSRI		Akathisia, tremor, serotonin syndrome	+
Antiemetics		Akathisia, dystonia, parkinsonism	+++
Antipsychotics
Typical		Akathisia, dystonia, tremor, OBLFD, NMS	+++
Atypical	Aripiprazole	Akathisia, dystonia, tremor, OBLFD, NMS	+ - ++
Adrenergic agents (sympathomimetics)		Tremor	++
Amiodirone		Tremor, parkinsonism	++
Dopamine depleters		Parkinsonism	+++
Antiepilectic agents	Phenytoin	Chorea with toxicity	++
	Lamotrigine	Tremor, chorea	+
	Valproate	Tremor parkinsonism	+++e ++f

OBLD refers to oral buccal lingual facial dyskinesia; NMS, neuroleptic malignant syndrome
aGait ataxia with high doses
bNo longer available in the US
cClozapine appears to be the atypical antipsychotic that is least likely to cause DIMDs
dOnly available in the US as part of special clinical trials or compassionate use
e40% of people will develop a fine postural tremor
f5% of elderly will develop parkinsonism
+ rare
++ uncommon
+++ common