Neurology · Movement Disorders
The facts most likely to be tested
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Parkinson disease is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta leading to a deficiency of dopamine in the striatum.
The cardinal motor symptoms include resting tremor, bradykinesia, cogwheel rigidity, and postural instability.
The resting tremor is classically described as a pill-rolling tremor that improves with voluntary movement.
Lewy bodies, which are intracellular inclusions composed of alpha-synuclein, are the pathognomonic histopathological finding.
Levodopa/carbidopa is the most effective symptomatic treatment for motor symptoms, though long-term use is associated with motor fluctuations and dyskinesias.
Dopamine agonists such as pramipexole or ropinirole are often used as initial therapy in younger patients to delay the need for levodopa.
Deep brain stimulation is a surgical option for patients with medically refractory symptoms or severe levodopa-induced dyskinesias.
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A 68-year-old male presents to the clinic with a 6-month history of progressive difficulty walking and stiffness. On examination, he exhibits a resting tremor in his right hand, bradykinesia during finger tapping, and cogwheel rigidity upon passive range of motion of the upper extremities. He also demonstrates a masked facies and a shuffling gait with reduced arm swing. He has no history of neuroleptic use or exposure to dopamine-blocking agents.
What is the most likely diagnosis?
Parkinson disease
The patient presents with the classic triad of resting tremor, bradykinesia, and rigidity, which are the hallmark clinical features of Parkinson disease as described in the second bet.
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Etiology / Epidemiology
Neurodegenerative disorder of dopaminergic neurons in the substantia nigra; typically presents in patients >60 years old.
Clinical Manifestations
Classic triad: resting tremor, bradykinesia, and rigidity; pill-rolling tremor is pathognomonic.
Diagnosis
Clinical diagnosis based on bradykinesia plus at least one other cardinal sign; MRI is used to rule out mimics.
Treatment
Levodopa/Carbidopa is the most effective therapy; avoid dopamine antagonists like metoclopramide.
Prognosis
Progressive decline; falls and aspiration pneumonia are the leading causes of mortality.
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Epidemiology & Etiology
Idiopathic Parkinson disease is the most common movement disorder in the elderly. Environmental exposure to pesticides and heavy metals may increase risk, while smoking is paradoxically associated with a lower incidence.
Pertinent Anatomy
The primary pathology involves the substantia nigra pars compacta within the basal ganglia. Loss of these neurons disrupts the nigrostriatal pathway, leading to an imbalance between excitatory and inhibitory motor signals.
Pathophysiology
The hallmark is the accumulation of Lewy bodies, which are intracellular inclusions composed of alpha-synuclein. This protein aggregation leads to the death of dopaminergic neurons, resulting in a profound dopamine deficiency in the striatum.
Clinical Manifestations
Patients present with pill-rolling tremor, bradykinesia (slowness of movement), and cogwheel rigidity. Look for masked facies, shuffling gait, and micrographia. Postural instability is a late-stage finding; early falls suggest atypical parkinsonism.
Diagnosis
Diagnosis is strictly clinical, requiring bradykinesia plus either resting tremor or rigidity. DaTscan (SPECT imaging) can be used to visualize dopamine transporter loss if the diagnosis is uncertain. MRI is essential to exclude structural lesions or normal pressure hydrocephalus.
Treatment
Levodopa/Carbidopa is the gold standard for symptom control. In younger patients, dopamine agonists (e.g., pramipexole) may be used to delay levodopa-related motor fluctuations. Avoid typical antipsychotics as they worsen symptoms; use quetiapine if psychosis develops.
Prognosis
Disease is progressive with no cure. Dementia develops in up to 80% of patients over time. Monitor for orthostatic hypotension and dysphagia, which significantly increase morbidity.
Differential Diagnosis
Essential tremor: action tremor, no bradykinesia
Multiple system atrophy: early autonomic dysfunction
Progressive supranuclear palsy: vertical gaze palsy
Drug-induced parkinsonism: history of antipsychotic use
Normal pressure hydrocephalus: urinary incontinence and gait ataxia