Bit · Neuro
Parkinson vs Essential Tremor vs Huntington vs Wilson
Four movement disorders with characteristic tremors and additional features. The pivot is the type of movement and the accompanying signs.
Mechanism
Each disorder localizes to a different region of the basal ganglia or cerebellum and produces a characteristic motor phenotype:
- Parkinson disease — loss of dopaminergic neurons in substantia nigra pars compacta. Lewy bodies (α-synuclein). TRAP: Tremor (resting, pill-rolling, ~4–6 Hz; better with intentional movement), Rigidity (cogwheel), Akinesia/Bradykinesia, Postural instability. Mask-like facies, micrographia, shuffling gait. Treat: L-DOPA + carbidopa; dopamine agonists.
- Essential tremor — most common movement disorder. Action/intention tremor (worse with movement, better at rest — opposite of Parkinson). Often bilateral, postural. Autosomal dominant. Improves with alcohol. Treat: propranolol or primidone.
- Huntington disease — autosomal dominant, CAG trinucleotide repeat expansion on chromosome 4 (HTT gene). Anticipation: each generation, more repeats, earlier onset. Chorea (irregular dance-like jerky movements), psychiatric (depression, mood changes, psychosis), dementia. Caudate atrophy on MRI. Treat: VMAT2 inhibitors (tetrabenazine), antipsychotics for chorea.
- Wilson disease — autosomal recessive copper accumulation due to ATP7B mutation. Copper deposits in liver (cirrhosis), brain (basal ganglia → parkinsonism, dystonia, tremor, dysarthria, psychiatric changes), cornea (Kayser-Fleischer rings). Low ceruloplasmin, high urinary copper. Treat: zinc + penicillamine or trientine; liver transplant.
Differentiator Table
| Disorder | Movement | Other features | Pathology | Treatment |
|---|---|---|---|---|
| Parkinson | Resting pill-rolling tremor (better with movement) | TRAP — Tremor, Rigidity, Akinesia, Postural instability; mask facies | α-synuclein Lewy bodies in SN | L-DOPA + carbidopa; DA agonists; MAO-B inhibitors |
| Essential tremor | Action / postural tremor (worse with movement) | Bilateral, often hands; family history; improves with alcohol | Cerebellar / thalamic dysfunction | Propranolol; primidone |
| Huntington | Chorea (jerky dance-like) | Psychiatric + dementia + family history | CAG trinucleotide expansion, HTT gene, chr 4; caudate atrophy | Tetrabenazine; supportive |
| Wilson | Tremor + parkinsonism + dystonia | Kayser-Fleischer rings, liver disease, psychiatric, young onset (<40) | ATP7B mutation; copper deposition | Zinc + penicillamine / trientine |
The Pivot
Two questions:
- Resting or action tremor? Resting → Parkinson. Action → essential tremor.
- Additional features: chorea + psychiatric + family history → Huntington. Liver disease + Kayser-Fleischer rings in a young patient → Wilson.
NBME-Style Stem
A 22-year-old man presents with progressive tremor, dysarthria, and changes in personality. Examination shows a wing-beating tremor of the outstretched arms and golden-brown rings at the corneal limbus on slit-lamp exam. Liver function tests are abnormal. Serum ceruloplasmin is decreased. Which of the following is the most likely diagnosis?
Concept Anchor
Each movement disorder is a different basal ganglia or cerebellar lesion expressed as a specific movement: dopamine loss → resting tremor (Parkinson); cerebello-thalamic dysfunction → action tremor (essential); caudate atrophy → chorea (Huntington); copper → mixed extrapyramidal + KF rings (Wilson).