What is the testing and diagnosis process for hemiplegic dystonia?

Diagnostic Approach for Hemiplegic Dystonia

The diagnosis of hemiplegic dystonia requires a comprehensive assessment including clinical evaluation, neuroimaging, and laboratory tests to identify the underlying cause and distinguish it from other movement disorders affecting hemiplegic limbs. 1

Clinical Assessment

• Evaluate for core symptoms of dystonia in the hemiplegic limb, including abnormal postures, involuntary muscle contractions, and movement-triggered symptoms 1
• Assess for preservation of consciousness during dystonic episodes, which helps differentiate from seizure disorders 1
• Document the duration of dystonic episodes, as this can help distinguish between different types of movement disorders (hemiplegic dystonia episodes typically last less than 1 minute when paroxysmal) 1
• Perform a musculoskeletal evaluation to identify any joint subluxation, contractures, or soft tissue injuries that may contribute to abnormal posturing 1
• Evaluate for spasticity, which commonly coexists with dystonia in hemiplegic limbs 1
• Test for regional sensory changes that may indicate central pain components 1

Diagnostic Tests

Neuroimaging

• Brain MRI is essential to identify stroke lesions, demyelinating disease, or other structural abnormalities that may cause hemiplegic dystonia 1
• CT scan may be used to assess for intracranial calcification which can be associated with certain metabolic causes of dystonia 1

Laboratory Tests

• Thyroid function tests (serum T3/FT3, T4/FT4, TSH) to rule out hyperthyroidism 1
• Assessment of calcium and phosphorus metabolism (serum calcium, phosphorus, parathyroid hormone, calcitonin) 1
• Blood glucose testing to exclude glucose metabolism disorders 1
• Bilirubin levels to rule out kernicterus as a cause 1
• Serum ceruloplasmin levels to exclude Wilson's disease 1

Neurophysiological Testing

• EEG to rule out seizure disorders that may mimic dystonic movements 1
• Neurophysiological tests can help describe the pathophysiological mechanisms underlying the disorder 2

Differential Diagnosis

Movement Disorders That May Mimic Hemiplegic Dystonia

• Hemiplegic spasticity (differentiated by velocity-dependent resistance to passive movement) 1
• Seizures (differentiated by impaired consciousness and EEG abnormalities) 1
• Psychogenic movement disorders (characterized by distractibility, variability of presentations, and suggestibility) 1
• Tics (typically briefer jerks or postures than dystonic movements) 1
• Hyperekplexia (characterized by excessive startle response) 1

Post-Stroke Conditions That May Present Similarly

• Shoulder-hand syndrome/Complex Regional Pain Syndrome (CRPS) (diagnosed based on pain, tenderness, edema, trophic skin changes) 1
• Central post-stroke pain (characterized by burning or aching pain with allodynia) 1

Special Considerations

• In children, consider transient dystonia of infancy, which consists of paroxysmal episodes of abnormal upper limb posture with occasional trunk and lower limb involvement 1
• In adults with stroke, hemiplegic dystonia may be masked by or confused with spasticity, requiring careful clinical assessment 1, 3
• Botulinum toxin injections may be useful both diagnostically and therapeutically, as response can help confirm the dystonic nature of the posturing 1, 2

Red Flags Suggesting Alternative Diagnoses

• Duration of attacks exceeding 1 minute (suggests alternative diagnosis) 1
• Age of onset over 20 years without clear etiology (suggests secondary causes) 1
• Abnormalities in brain CT/MRI or presence of other neurologic problems 1
• No response to appropriate medications 1
• Abnormal results of interictal examinations 1

Diagnostic Algorithm

1. Confirm dystonic features in hemiplegic limb (abnormal postures, involuntary movements)
2. Perform brain MRI to identify structural lesions
3. Complete laboratory workup to exclude metabolic causes
4. Perform EEG to rule out seizure disorders
5. Consider trial of low-dose sodium channel blockers or botulinum toxin if paroxysmal kinesigenic dystonia is suspected
6. If diagnosis remains unclear, consider referral to movement disorder specialist 1, 2

By following this systematic approach, clinicians can accurately diagnose hemiplegic dystonia and distinguish it from other movement disorders affecting hemiplegic limbs, leading to appropriate treatment and improved outcomes for patients.