What are the causes of involuntary movements of a single upper limb?

Causes of Involuntary Movements of a Single Upper Limb

The most critical first step is to exclude stroke or seizure as the cause, as these represent life-threatening emergencies requiring immediate neuroimaging and intervention. 1

Immediate Life-Threatening Causes (Must Exclude First)

Acute Stroke

• Obtain immediate CT or MRI if stroke is suspected, particularly when involuntary movements are accompanied by facial droop, dysarthria, sensory loss, weakness, or visual field defects 1
• Post-stroke movement disorders occur in 1-4% of strokes and can affect the contralateral upper limb when involving the basal ganglia, thalamus, or their connections 2
• Thalamic lesions specifically can cause two distinct patterns: choreoathetosis (most prominent during finger-to-nose testing) or postural tremor (3-4 Hz, appearing after reaching target position) 3
• Movement disorders may appear immediately after stroke or develop months later as a delayed phenomenon 3

Focal Motor Seizures

• Present as rhythmic, synchronous, repetitive involuntary movements (20-100 movements) of one hand that may progress to other body parts 1
• Look for post-ictal confusion or Todd's paralysis following the episode 1
• Requires EEG and neurology consultation for definitive diagnosis 1

Metabolic and Systemic Causes

Hepatic Encephalopathy

• Asterixis (flapping tremor) is a negative myoclonus characterized by loss of postural tone, easily elicited by wrist hyperextension with separated fingers 4
• Can also manifest in feet, legs, arms, tongue, and eyelids 4
• Not pathognomonic—also occurs in uremia and other metabolic disorders 4
• Associated with altered consciousness in advanced stages, though early hepatic encephalopathy may present with isolated motor signs 4

Other Metabolic Disorders

• Hyperthyroidism, calcium-phosphate metabolism disorders (hypoparathyroidism, pseudoparathyroidism), and glucose metabolism disorders must be excluded 4

Movement Disorder Causes

Paroxysmal Kinesigenic Dyskinesia (PKD)

• Strongly consider if movements are triggered by sudden voluntary actions and last less than 1 minute (occurs in >98% of cases) 1
• Presents as dystonia, chorea, ballism, or combinations thereof 4
• Consciousness remains preserved during attacks 4
• Responds excellently to low-dose carbamazepine or oxcarbazepine 4
• Red flags suggesting alternative diagnosis: duration >1 minute, age of onset >20 years, abnormal brain imaging, no response to anticonvulsants 4

Functional Neurological Disorder (FND)

• Functional tremor can be entrained to stillness by using the unaffected limb to dictate a new rhythm (e.g., tapping or opening/closing the hand) 4
• Characterized by distractibility, variability of presentations, and suggestibility 4
• Red flags include adult onset, altered responsiveness during attacks, additional psychogenic signs, and atypical medication response 4
• Treatment focuses on retraining normal movement patterns rather than splinting or adaptive equipment 4

Dystonia

• Characterized by excessive muscle contraction in terms of strength, spread, and duration 5
• When affecting a single upper limb, encourage optimal postural alignment, even weight distribution, and graded activities using normal movement techniques 4
• Avoid prolonged end-range positioning and discourage "nursing" the affected limb 4
• Recent evidence emphasizes sensorimotor cortex involvement in focal dystonia 5

Chorea

• Purposeless, involuntary, non-stereotypical movements that can be predominantly unilateral 1
• Responds to benzodiazepines and D2 receptor blockers 5
• In systemic lupus erythematosus-related chorea, consider dopamine antagonists with or without immunosuppression 6

Myoclonus

• Can be caused by abrupt muscle contraction or sudden cessation (negative myoclonus) 5
• Before initiating treatment, obtain detailed medication history regarding substance withdrawal or caffeine excess, as these commonly cause jerky movements 6
• Lamotrigine is the first-line agent for myoclonus due to proven efficacy and excellent safety profile 6
• Sodium valproate is contraindicated in women of childbearing potential due to teratogenicity 6

Tremor

• Can be associated with basal ganglia, cerebellar, or thalamic dysfunction, but sensorimotor cortex involvement is increasingly recognized 5
• Thalamic lesions can produce 3-4 Hz postural tremor with reciprocal EMG discharges between forearm extensors and flexors 3

Age-Specific Considerations in Infants

Transient Dystonia of Infancy

• Paroxysmal episodes of abnormal upper limb posture, occasionally involving trunk and single lower limb 4
• Onset typically 5-10 months, resolves between 3 months and 5 years 4
• Normal interictal examination and neuroimaging 4

Benign Myoclonus of Early Infancy

• Myoclonic jerks of head and/or upper limbs occurring in clusters 4
• Onset 4-7 months, ceases by age 2 years 4
• Requires normal ictal EEG, neurological status, and development to confirm diagnosis 4

Drug-Induced Causes

Antipsychotic-Induced Movement Disorders

• Haloperidol and other antipsychotics cause extrapyramidal symptoms (EPS) frequently, especially in first few days of treatment 7
• Acute dystonia (spasm of neck muscles, throat tightness, difficulty breathing) occurs more frequently in males and younger age groups 7
• Tardive dyskinesia presents as potentially irreversible, rhythmical involuntary movements of tongue, face, mouth, or jaw, sometimes accompanied by involuntary movements of extremities 7
• Risk is greater in elderly patients on high-dose therapy, especially females 7

Periodic Limb Movements

• Common in patients taking antidepressants 4
• Each movement lasts 2-4 seconds with frequency of 1 every 20-40 seconds 4

Common Pitfalls to Avoid

• Do not assume all unilateral upper limb movements are benign—always exclude stroke and seizure first 1
• Do not provide adaptive equipment or splinting in acute phase of functional movement disorders, as this prevents restoration of normal movement patterns and may worsen symptoms 4
• Do not use cocontraction or muscle tensing to suppress tremor, as this is not a helpful long-term strategy 4
• Do not diagnose tardive dyskinesia without considering that fine vermicular tongue movements may be an early sign—stopping medication at this stage may prevent full syndrome development 7
• Do not overlook delayed-onset movement disorders after stroke, which can appear months after the initial event 3