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).