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Parkinson's Disease: Motor Symptoms, Pathophysiology, and Management

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra pars compacta, leading to striatal dopamine deficiency.

Cardinal Motor Signs (TRAP)

  • Tremor: Resting, 4–6 Hz "pill-rolling"; asymmetric onset; improves with action, worsens with stress.
  • Rigidity: "Lead-pipe" (uniform) or "cogwheel" (with tremor); axial + appendicular.
  • Bradykinesia: Slowness + decrement in amplitude/speed of repetitive movements; required for diagnosis.
  • Postural Instability: Late feature (Hoehn & Yahr stage 3+); impaired righting reflexes → falls.

Non-Motor Symptoms (Often Precede Motor)

  • Autonomic: Constipation, orthostatic hypotension, urinary urgency, sexual dysfunction.
  • Neuropsychiatric: Depression, anxiety, apathy, psychosis (medication-related), cognitive decline → dementia (PDD).
  • Sleep: RBD (strong prodromal marker), insomnia, excessive daytime sleepiness.
  • Sensory: Hyposmia (early), pain, paresthesias.

Impact on Movement

  • Gait: Shuffling, festination, reduced arm swing, freezing of gait (FOG).
  • Fine motor: Micrographia, buttoning, typing difficulty.
  • Speech: Hypophonia, monotone, festinating speech.
  • ADLs: Progressive dependence; OFF periods (medication wearing off) cause fluctuations.

Treatment Strategy

  1. Levodopa/Carbidopa: Gold standard; replaces dopamine. Start low, titrate. Motor complications (dyskinesia, fluctuations) with long-term use.
  2. Dopamine agonists (pramipexole, ropinirole): Early monotherapy (younger) or adjunct; impulse control disorder risk.
  3. MAO-B inhibitors (rasagiline, selegiline): Mild symptomatic benefit; possible neuroprotection (debated).
  4. COMT inhibitors (entacapone, opicapone): Extend levodopa half-life.
  5. Amantadine: For dyskinesia.
  6. Deep Brain Stimulation (DBS): STN or GPi; for motor complications refractory to meds. Not curative.
  7. Exercise: High-intensity aerobic + resistance + balance – only intervention with disease-modifying potential (neuroplasticity).

Multidisciplinary Care

Movement disorder specialist + PT/OT/SLP + neuropsychology + palliative care (late stage) + social work.

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