Parkinson Disease
A progressive brain disorder that leads to shaking, stiffness, and difficulty with walking, balance, and coordination.
Emergency Management: Aspiration pneumonia due to severe dysphagia is the most common fatal event. Acute psychosis secondary to dopaminergic medications may require hospital admission and treatment with Quetiapine or Pimavanserin.
Parkinson Disease is a progressive neurodegenerative disorder characterized primarily by the loss of dopaminergic neurons in the substantia nigra pars compacta. It presents with a classic tetrad of motor symptoms: resting tremor, bradykinesia, rigidity, and postural instability.
Detailed Overview
Beyond the classic motor features, PD encompasses a wide array of non-motor symptoms, including REM sleep behavior disorder, anosmia, autonomic dysfunction, and cognitive decline, which often precede motor symptoms by years. The pathological hallmark is the presence of Lewy bodies (intraneuronal aggregates of misfolded alpha-synuclein). Symptoms typically emerge asymmetrically. Current treatments manage symptoms but do not halt disease progression.
Epidemiology & Demographics
Affects 1-2% of the population over age 65. The second most common neurodegenerative disease after Alzheimer's. Male-to-female ratio is roughly 1.5:1. Average age of onset is 60 years.
Etiological Mechanism
Most cases are sporadic/idiopathic. A complex interaction between aging, environmental exposures (pesticides), and genetic susceptibility.
Primary Causes
Loss of dopamine-producing neurons in the basal ganglia. Monogenic forms (SNCA, LRRK2, PRKN, PINK1) account for ~10% of cases, primarily in early-onset PD.
Misfolded alpha-synuclein aggregates to form Lewy bodies and Lewy neurites within neurons, causing cellular toxicity and death. The specific loss of dopaminergic neurons in the substantia nigra pars compacta disrupts the nigrostriatal pathway. This leads to reduced activation of the direct pathway and increased activation of the indirect pathway in the basal ganglia, resulting in a net inhibition of the motor cortex (thalamic output), causing poverty of movement (bradykinesia and rigidity). Motor symptoms typically become apparent when >60% of substantia nigra neurons are lost.
Diagnostic Criteria & Guidelines
Clinical diagnosis based on the UK Brain Bank criteria: Requires bradykinesia PLUS at least one of resting tremor or rigidity. There must be an absence of atypical features (e.g., early severe autonomic failure, supranuclear gaze palsy) and a clear, robust response to dopaminergic therapy.
Levodopa/Carbidopa (starts at 25/100 mg PO TID) is the most effective drug for motor symptoms. Dopamine agonists (Pramipexole 0.125 mg TID, Ropinirole) or MAO-B inhibitors (Rasagiline 1 mg daily) are often used initially in younger patients (<65) to delay starting Levodopa and prevent dyskinesias.
Second-Line & Adjunctive Therapy
COMT inhibitors (Entacapone 200 mg with each Levodopa dose) to extend Levodopa half-life and reduce 'off' time. Amantadine (100 mg BID) for treating levodopa-induced dyskinesias.
Surgical & Procedural Management
Deep Brain Stimulation (DBS) of the Subthalamic Nucleus (STN) or Globus Pallidus internus (GPi). Highly effective for patients with severe motor fluctuations or disabling dyskinesias who still respond well to levodopa.
Patient Counseling & Advice
Warn about potential side effects of dopamine agonists, particularly impulse control disorders (gambling, hypersexuality, binge eating) and sudden sleep attacks. Explain that protein interferes with Levodopa absorption, so take it 30 mins before meals.
Follow-Up & Monitoring Schedule
Neurology visits every 3-6 months to adjust medications based on the emergence of motor fluctuations ('wearing off') and dyskinesias. Annual screen for depression and cognitive changes.
Preventive Strategies
No proven primary prevention. Caffeine consumption, smoking, and vigorous exercise are epidemiologically associated with a lower risk of developing PD.
Progressive disease. Life expectancy is normal to slightly reduced. Late-stage disease is characterized by severe disability, falls, and dementia.