Movement disorders and neurodegenerative diseases
This domain tests pattern recognition in hypokinetic and hyperkinetic syndromes, red flags that separate atypical from idiopathic parkinsonism, and the pharmacology of dopaminergic treatment.
Parkinson disease
Diagnosis requires bradykinesia plus rest tremor or rigidity, with asymmetric onset, clear levodopa response and no red flags. Treatment: levodopa/carbidopa is most effective; dopamine agonists and MAO-B inhibitors are used early or as adjuncts; amantadine helps dyskinesia; device-aided therapy includes subcutaneous apomorphine, intrajejunal levodopa and deep brain stimulation of the subthalamic nucleus or globus pallidus internus. Motor fluctuations include wearing-off, on–off phenomena and peak-dose dyskinesia.
Red flags for atypical parkinsonism
Early falls, vertical supranuclear gaze palsy or slow saccades (PSP), early severe dysautonomia or cerebellar signs with the hot-cross-bun sign (MSA), apraxia, alien limb and cortical sensory loss (corticobasal degeneration), early dementia with visual hallucinations and fluctuation (dementia with Lewy bodies), absent levodopa response and rapid progression.
Tremor
Rest tremor suggests parkinsonism; postural and action tremor suggests essential tremor (bilateral, improves with alcohol, treated with propranolol or primidone); intention tremor suggests a cerebellar lesion; dystonic tremor is irregular and positional.
Hyperkinetic disorders
Huntington disease: CAG repeat >36, chorea, cognitive decline, psychiatric features, caudate atrophy; tetrabenazine or deutetrabenazine for chorea. Dystonia: focal forms (cervical dystonia, blepharospasm) respond to botulinum toxin. Tics are suppressible with a premonitory urge. Restless legs syndrome responds to dopamine agonists and iron repletion. Drug-induced syndromes include parkinsonism (antipsychotics, metoclopramide), acute dystonia, akathisia and tardive dyskinesia.
Ataxia and metabolic causes
Spinocerebellar ataxias are autosomal dominant; Friedreich ataxia is recessive with cardiomyopathy. Screen young patients with extrapyramidal signs for Wilson disease (ceruloplasmin, 24-hour urinary copper, Kayser–Fleischer rings, MRI).
Worked example
A 65-year-old has 18 months of asymmetric right-hand rest tremor, slowness, micrographia and a clear response to levodopa without falls or gaze palsy. This is idiopathic Parkinson disease; adding a dopamine agonist or MAO-B inhibitor is reasonable, and if dyskinesia emerges, amantadine or device-aided therapy should be considered.
Traps
Calling every tremor Parkinson disease; missing Wilson disease in a young patient; diagnosing essential tremor when the tremor is dystonic; failing to ask about antipsychotic and antiemetic exposure.