What is the treatment for drug-induced Parkinsonism?

Treatment for Drug-induced Parkinsonism

The first-line treatment for drug-induced parkinsonism is discontinuation of the offending medication whenever possible. 1 When the causative agent cannot be discontinued, dose reduction or switching to an alternative medication with lower risk for parkinsonism should be considered.

Diagnosis and Clinical Features

Drug-induced parkinsonism (DIP) is one of the most common iatrogenic movement disorders, characterized by:

• Tremors
• Bradykinesia (slowness of movement)
• Rigidity
• Shuffling gait with postural instability

These symptoms are often clinically indistinguishable from idiopathic Parkinson's disease, but some distinguishing features may include:

• Acute to subacute onset while taking a dopamine receptor blocking agent (DRBA)
• More symmetrical presentation
• Less prominent resting tremor
• Association with other drug-induced movement disorders like tardive dyskinesia

Treatment Algorithm

Step 1: Identify and Address the Causative Agent

• Discontinue the offending medication if clinically possible 1
• If discontinuation is not possible:
  • Reduce the dose of the causative agent
  • Switch to medications with lower risk of parkinsonism:
    • For antipsychotics: Consider quetiapine or clozapine 1

Step 2: Symptomatic Treatment (if symptoms persist)

For mild to moderate symptoms:

• Anticholinergic medications:
  • Trihexyphenidyl: Initial dose 1 mg daily, increased by 2 mg increments every 3-5 days until optimal response (typically 5-15 mg daily in divided doses) 2
  • Use cautiously in elderly patients due to increased risk of cognitive side effects

For moderate to severe symptoms:

• Amantadine: Effective for drug-induced extrapyramidal reactions with lower incidence of anticholinergic side effects 3
  • Typical dosage: 100 mg 2-3 times daily

For persistent symptoms with suspected underlying Parkinson's disease:

• Consider levodopa therapy, particularly in patients with DIP and prodromal PD 4

Special Considerations

Elderly Patients

• Higher risk for developing DIP due to age-related changes in dopamine function
• More sensitive to medication effects; use lower doses of anticholinergics
• "Start low, go slow" approach is essential 5
• Monitor for anticholinergic side effects (confusion, urinary retention, dry mouth)

Monitoring and Follow-up

• Regular assessment using standardized scales like the Abnormal Involuntary Movement Scale (AIMS)
• Avoid abrupt withdrawal of treatment as this may result in acute exacerbation of symptoms 2
• Complete remission typically takes 6-18 months in most patients after discontinuation of the offending agent 6

Prevention

• Awareness of medications with potential to cause DIP
• Careful medication selection, particularly in high-risk patients (elderly, females, those with cognitive impairment)
• Avoid polypharmacy when possible
• Use lowest effective dose of high-risk medications

Important Caveats

1. Persistence of symptoms: Up to 10% of patients may have persistent symptoms even after discontinuation of the causative agent, suggesting unmasking of underlying Parkinson's disease 7

2. Diagnostic challenges: In cases where the diagnosis is uncertain, functional neuroimaging tests like DaTscans can help distinguish between DIP and idiopathic Parkinson's disease 1

3. Prophylactic treatment: Prophylactic treatment with anticholinergics is not indicated 1

4. Medication withdrawal: Abrupt withdrawal of treatment for parkinsonism may result in acute exacerbation of symptoms or neuroleptic malignant syndrome 2

By following this treatment approach and considering these special factors, most patients with drug-induced parkinsonism can achieve significant symptom improvement or complete resolution.