Parkinson's Disease: Features, Diagnosis and Treatment

Parkinson's disease is a progressive neurodegenerative disorder caused by loss of dopamine-producing neurons in the substantia nigra of the brain. It is the second most common neurodegenerative disease after Alzheimer's disease, usually starting after the age of 60. Treatment does not stop the disease but can greatly improve symptoms.

Core motor features

Parkinsonism is diagnosed with bradykinesia plus rest tremor and/or rigidity. These features are usually asymmetrical at onset.

• Bradykinesia — slowness of movement, with progressive reduction in speed and size of repetitive movements (for example finger tapping).
• Rest tremor — a "pill-rolling" tremor of about 4–6 Hz that improves with movement.
• Rigidity — increased tone throughout the movement ("lead-pipe"), with "cogwheeling" when tremor is present.
• Postural instability — usually a later feature, leading to falls.

Other signs:

• a reduced facial expression (hypomimia)
• a soft voice
• small handwriting (micrographia)
• reduced arm swing
• a shuffling gait with freezing

Non-motor features

These are common and often appear years before the motor symptoms:

• loss of smell
• REM sleep behaviour disorder (acting out dreams)
• constipation
• depression and anxiety
• postural hypotension
• urinary symptoms
• cognitive impairment and dementia later in the disease
• hallucinations

Diagnosis

The diagnosis is clinical, based on history and examination, supported by a good response to levodopa. Brain imaging is usually normal; it helps exclude other causes. A dopamine transporter scan (DaTscan) can help in uncertain cases.

Mimics to consider

• Drug-induced parkinsonism: antipsychotics, metoclopramide and prochlorperazine. This is usually symmetrical, and tremor is less common.
• Essential tremor: a postural or action tremor, often with a family history, improved by alcohol.
• Vascular parkinsonism: mainly affects the legs and gait.
• "Parkinson-plus" syndromes:
  • progressive supranuclear palsy (vertical gaze palsy, early falls)
  • multiple system atrophy (early autonomic failure)
  • dementia with Lewy bodies (early dementia and hallucinations)
  These respond poorly to levodopa.

Treatment

• Levodopa combined with a decarboxylase inhibitor (carbidopa or benserazide) — the most effective drug for motor symptoms. Long-term use is associated with motor fluctuations ("wearing off") and dyskinesias.
• Dopamine agonists (for example pramipexole, ropinirole, rotigotine patch). Side effects:
  • impulse control disorders, such as gambling, hypersexuality and compulsive shopping (warn patients and families)
  • sleepiness
  • hallucinations
• MAO-B inhibitors (rasagiline, selegiline) and COMT inhibitors (entacapone) as add-ons.
• Non-drug care: physiotherapy, occupational therapy, speech and swallowing therapy, and exercise.
• Advanced disease: deep brain stimulation, apomorphine or intestinal levodopa gel in selected patients.
• Non-motor symptoms: treat them too, for example depression, constipation and postural hypotension.

Important safety points

• Never stop Parkinson's medicines suddenly, for example when a patient is "nil by mouth" in hospital. Abrupt withdrawal can cause a dangerous syndrome resembling neuroleptic malignant syndrome. Give medicines on time.
• Avoid dopamine-blocking drugs, such as haloperidol and metoclopramide. Domperidone is a safer antiemetic, with cardiac cautions.

Exam pearls

• Asymmetry at onset suggests idiopathic Parkinson's disease.
• Early falls and a vertical gaze palsy suggest progressive supranuclear palsy.
• Dopamine agonists can cause impulse control disorders.

For more, see our Exam Night Notes 1.0: Neurology and the neurology chapter of the Medicine Companion.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. Which feature is required to diagnose parkinsonism?

   1. Postural instability
   2. Bradykinesia
   3. Rest tremor
   4. Rigidity
   5. Dementia
   Show answer

   Answer: B. Bradykinesia
   Bradykinesia plus rest tremor and/or rigidity.

2. Which drug class can cause impulse control disorders such as gambling?

   1. COMT inhibitors
   2. Dopamine agonists
   3. Anticholinergics
   4. Levodopa only
   5. MAO-B inhibitors
   Show answer

   Answer: B. Dopamine agonists
   Dopamine agonists (pramipexole, ropinirole) are especially linked to impulse control disorders.

3. A patient with Parkinson's disease is vomiting in hospital. Which antiemetic is preferred?

   1. Droperidol
   2. Haloperidol
   3. Domperidone (with cardiac cautions)
   4. Prochlorperazine
   5. Metoclopramide
   Show answer

   Answer: C. Domperidone (with cardiac cautions)
   Domperidone does not cross the blood–brain barrier much; dopamine antagonists worsen parkinsonism.

4. Early falls and vertical gaze palsy suggest:

   1. Wilson's disease
   2. Multiple sclerosis
   3. Progressive supranuclear palsy
   4. Essential tremor
   5. Idiopathic Parkinson's disease
   Show answer

   Answer: C. Progressive supranuclear palsy
   PSP presents with early falls and vertical gaze palsy, with poor levodopa response.

5. Why must Parkinson's medicines not be stopped suddenly?

   1. They cause seizures
   2. No reason
   3. They lower blood sugar
   4. Abrupt withdrawal can cause a syndrome like neuroleptic malignant syndrome
   5. They are addictive
   Show answer

   Answer: D. Abrupt withdrawal can cause a syndrome like neuroleptic malignant syndrome
   Missing doses causes severe rigidity and a potentially fatal hyperpyrexic syndrome.

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Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.