Parkinson's Disease: Causes, Symptoms & Treatment

Parkinson's disease (PD) is a progressive neurodegenerative disorder that primarily affects movement. It develops when nerve cells (neurons) in a region of the brain called the substantia nigra, which produces the neurotransmitter dopamine, gradually deteriorate and die. Dopamine plays a crucial role in coordinating smooth, purposeful movement, and its deficiency leads to the hallmark motor symptoms of Parkinson's disease.

Parkinson's disease affects approximately 1 million people in the United States and 10 million worldwide. It is the second most common neurodegenerative disease after Alzheimer's, with an average age of onset around 60 years, though early-onset PD can occur before age 50.

The exact cause of Parkinson's disease is unknown, but a combination of genetic and environmental factors contributes:

• Age: The greatest risk factor; risk increases with age
• Genetics: Approximately 10-15% of cases have a genetic component (LRRK2, GBA, SNCA, Parkin genes)
• Environmental exposures: Pesticide and herbicide exposure, rural living, well water consumption
• Sex: Men are 1.5 times more likely to develop PD than women
• Head trauma: History of traumatic brain injury may increase risk

Cardinal motor symptoms:

• Tremor: Resting tremor, typically starting in one hand ("pill-rolling" tremor); most common initial symptom
• Bradykinesia: Slowness of movement; difficulty initiating and executing movements
• Rigidity: Stiffness and resistance to passive movement in the limbs and trunk
• Postural instability: Impaired balance and coordination (typically later in the disease)

Non-motor symptoms:

• Depression and anxiety (affect up to 50% of patients)
• Sleep disorders (REM sleep behavior disorder, insomnia, excessive daytime sleepiness)
• Cognitive changes and dementia (especially in later stages)
• Loss of smell (hyposmia) -- often one of the earliest signs
• Constipation
• Urinary urgency
• Orthostatic hypotension (drop in blood pressure upon standing)
• Fatigue

Parkinson's disease is diagnosed clinically based on symptoms, neurological examination, and response to medication. There is no definitive blood test or imaging study for diagnosis:

• Neurological examination: Assessment of motor and non-motor symptoms
• Response to levodopa: Improvement with levodopa strongly supports the diagnosis
• DaTscan: SPECT imaging of dopamine transporters can help distinguish PD from essential tremor, but does not differentiate PD from other parkinsonian syndromes
• MRI: Primarily used to rule out other conditions

There is currently no cure for Parkinson's disease, but treatments can significantly manage symptoms:

Medications:

• Levodopa/carbidopa (Sinemet): The most effective treatment; converts to dopamine in the brain. Remains the gold standard for motor symptom control
• Dopamine agonists (pramipexole, ropinirole, rotigotine): Mimic dopamine; sometimes used first in younger patients
• MAO-B inhibitors (selegiline, rasagiline, safinamide): Block dopamine breakdown
• COMT inhibitors (entacapone, opicapone): Extend levodopa's duration of action
• Amantadine: Helps with dyskinesias (involuntary movements from long-term levodopa use)
• Anticholinergics (trihexyphenidyl): May help tremor in younger patients

Surgical treatments:

• Deep brain stimulation (DBS): Electrodes implanted in specific brain areas deliver electrical impulses; effective for motor fluctuations and tremor
• Focused ultrasound: Non-invasive procedure for tremor-dominant PD

Supportive therapies:

• Physical therapy for mobility, balance, and fall prevention
• Occupational therapy for daily activities
• Speech-language therapy (especially for voice volume and swallowing)
• Regular exercise (shown to slow disease progression -- especially high-intensity exercise, tai chi, boxing, and dancing)

See a neurologist if you develop tremor, notice that your movements are becoming slower, or if family members observe changes in your gait, posture, or facial expression. Early diagnosis and treatment can significantly improve quality of life.