Parkinson Disease

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.

• Age: The largest known risk factor; risk increases significantly past 60.
• Environmental toxins: Exposure to pesticides (e.g., Paraquat, Rotenone) and rural living/well water use.
• Genetics: Family history or presence of GBA or LRRK2 gene mutations.

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.

Characteristic Clinical Presentation

• Resting Tremor: A 'pill-rolling' tremor (4-6 Hz) present at rest, decreasing with voluntary movement. Usually starts unilaterally in a hand.
• Bradykinesia: Slowness of movement, reduced arm swing while walking, and progressive decrease in amplitude of repetitive movements (e.g., finger tapping).
• Rigidity: Increased resistance to passive joint movement, often 'cogwheel' in nature when tremor is superimposed.
• Non-motor symptoms: Constipation, anosmia (loss of smell), depression, and REM sleep behavior disorder (acting out dreams).

Physical Examination Signs

• Micrographia (abnormally small, cramped handwriting).
• Masked facies (hypomimia - reduced facial expression).
• Festinating gait (shuffling steps with stooped posture) and postural instability (positive pull test).

• Parkinson Disease Dementia (PDD): Cognitive impairment and visual hallucinations occurring late in the disease course.
• Dysphagia: Difficulty swallowing, leading to a high risk of aspiration pneumonia, the leading cause of death.
• Falls: Due to postural instability, leading to hip fractures and head trauma.

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.

Differential Diagnosis

• Essential Tremor
• Drug-induced Parkinsonism (e.g., from typical antipsychotics, metoclopramide)
• Multiple System Atrophy (MSA)
• Progressive Supranuclear Palsy (PSP)

Laboratory Tests & Biomarkers

• Routine Labs: Normal. Used only to rule out other conditions (e.g., ceruloplasmin for Wilson disease in young patients).

Imaging Modalities & Findings

• DaTscan (I-123 Ioflupane SPECT):
• Brain MRI:

• Hoehn and Yahr Stage 1
  Unilateral involvement only, minimal or no functional impairment.
• Hoehn and Yahr Stage 3
  Bilateral disease with mild to moderate disability, impaired postural reflexes, but physically independent.
• Hoehn and Yahr Stage 5
  Confinement to bed or wheelchair unless aided.

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.

Recommended Lifestyle Changes

• Intensive, regular aerobic exercise (e.g., cycling, boxing, Tai Chi) is highly recommended and may modify disease progression.
• Work with physical, occupational, and speech therapists (e.g., LSVT BIG and LOUD programs).
• Eat a high-fiber diet and maintain hydration to manage severe constipation.

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.