Dyskinesia
Summary
Dyskinesia refers to abnormal, involuntary muscle movements that can include tics, jerks, tremors, or writhing motions. It is commonly seen as a side effect of long-term dopaminergic therapy (e.g., levodopa in Parkinson's disease) or antipsychotic use (tardive dyskinesia). It can also result from basal ganglia dysfunction in various neurological disorders.
Detail
Dyskinesia encompasses a broad category of movement disorders characterized by involuntary muscle movements, which can manifest as chorea, athetosis, dystonia, tics, or tremors. Pathophysiologically, it is often linked to dysfunction in the basal ganglia circuitry, particularly imbalances in dopaminergic signaling in the direct and indirect pathways controlling movement.
Key clinical contexts include: 1. Levodopa-induced dyskinesia: Occurs in Parkinson's disease patients on long-term levodopa therapy, thought to result from pulsatile stimulation of dopamine receptors leading to altered receptor sensitivity and downstream signaling changes (non-physiologic, pulsatile dopaminergic stimulation causing postsynaptic changes).
2. Tardive dyskinesia: A delayed side effect of chronic antipsychotic use (especially typical/first-generation antipsychotics that block D2 receptors), characterized by repetitive, involuntary movements such as lip smacking, tongue protrusion, grimacing, and limb movements. Thought to result from dopamine receptor upregulation/supersensitivity after chronic blockade. Risk increases with duration of treatment; may be irreversible even after stopping the offending drug. Treatment includes VMAT2 inhibitors (valbenazine, deutetrabenazine).
3. Biliary dyskinesia: A separate clinical entity referring to abnormal gallbladder motility/contraction, often diagnosed via HIDA scan with CCK stimulation (low ejection fraction <35% supports diagnosis), presenting with biliary colic-type pain without gallstones.
4. Other causes: Huntington's disease (chorea), Wilson's disease, and other basal ganglia disorders can present with dyskinetic movements.
Clinical significance: Recognizing dyskinesia is crucial for medication management—balancing symptom control in Parkinson's disease while minimizing dyskinesia (e.g., using lower doses, extended-release formulations, or adjunct therapies like amantadine), and monitoring antipsychotic use for tardive dyskinesia with tools like the Abnormal Involuntary Movement Scale (AIMS).
Sources
- First Aid for the USMLE Step 1
- Kaplan USMLE Step 1 Pharmacology
- Harrison's Principles of Internal Medicine
- UpToDate: Tardive Dyskinesia
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