Movement disorders and neurodegeneration: Parkinson disease, tremor, ataxia, dementia
This domain tests pattern recognition across tremor, parkinsonism, ataxia and cognitive decline, with emphasis on separating idiopathic disease from atypical syndromes and on treatable mimics.
Parkinsonism
Parkinson disease requires bradykinesia plus rest tremor or rigidity, with asymmetric onset, sustained levodopa response, and no red flags. Atypical features within the first year - early falls, vertical supranuclear gaze palsy, prominent autonomic failure, hallucinations, or dementia - point to progressive supranuclear palsy, multiple system atrophy, corticobasal degeneration, or dementia with Lewy bodies. Treat with levodopa plus a decarboxylase inhibitor; add a monoamine oxidase B inhibitor, dopamine agonist, or catechol-O-methyltransferase inhibitor for fluctuations. Long-term complications include wearing-off, dyskinesias, impulse control disorder (dopamine agonists), and psychosis (use quetiapine or clozapine, avoid typical antipsychotics). Deep brain stimulation of the subthalamic nucleus or globus pallidus internus helps selected patients with tremor and fluctuations. Drug-induced parkinsonism (antipsychotics, metoclopramide) is symmetrical and usually resolves after withdrawal.
Tremor and ataxia
Essential tremor is bilateral, postural/kinetic, affects the arms and head, improves with alcohol, and responds to propranolol or primidone. Cerebellar tremor is intention-type with other cerebellar signs. Ataxia work-up includes B12, thyroid, coeliac serology, vitamin E, spinocerebellar ataxia genetics, Friedreich ataxia (GAA repeat, cardiomyopathy, absent reflexes), and paraneoplastic cerebellar degeneration.
Dementia
Alzheimer disease: insidious episodic memory loss with medial temporal atrophy, low CSF amyloid-beta 42 and raised tau, or positive amyloid PET. Vascular dementia: stepwise course with infarcts and white matter disease. Dementia with Lewy bodies: fluctuating cognition, recurrent visual hallucinations, REM sleep behaviour disorder, parkinsonism, and severe neuroleptic sensitivity. Frontotemporal dementia: behavioural change or progressive aphasia, with C9orf72, MAPT and GRN mutations. Normal pressure hydrocephalus: magnetic gait, urinary incontinence, cognitive slowing with ventriculomegaly. Creutzfeldt-Jakob disease: rapid decline, myoclonus, periodic EEG or cortical ribboning on DWI.
Worked example
A 72-year-old has a 2-year history of right-hand rest tremor, asymmetric bradykinesia, and good response to levodopa, with no falls or gaze palsy. This is Parkinson disease. Vertical supranuclear gaze palsy or early backward falls would instead suggest progressive supranuclear palsy, and early hallucinations with fluctuating attention would suggest dementia with Lewy bodies.
Traps
Do not diagnose Parkinson disease when red flags appear early. Typical antipsychotics can precipitate severe rigidity in Lewy body disease. Essential tremor is not a rest tremor. Rapidly progressive dementia with myoclonus should prompt CSF 14-3-3 and RT-QuIC testing for prion disease.