Parkinson's disease

Overview

•Classic triad: bradykinesia + resting tremor + rigidity - onset is asymmetrical (unilateral first)

•Bradykinesia - slowness/difficulty initiating movement; cardinal feature required for diagnosis

•Resting tremor - 3-5 Hz 'pill-rolling'; present at rest, suppressed by intentional movement

•Rigidity - cogwheel rigidity (ratchet-like) on passive movement

•Gait - shuffling, small steps (festination), freezing of gait

•Other motor: hypomimia (masked facies), micrographia, hypophonia

•Non-motor (may precede motor symptoms): anosmia, REM sleep behaviour disorder, depression/anxiety, constipation, orthostatic hypotension, cognitive impairment

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PD tremor is a RESTING tremor that IMPROVES with intentional movement. Essential tremor is an ACTION/POSTURAL tremor that WORSENS with movement - no bradykinesia or rigidity. Essential tremor is managed with propranolol.

Investigations

•Clinical diagnosis - made by a movement disorder specialist; investigations support, not replace, clinical judgement

•Routine bloods (FBC, TFTs, U&Es) - exclude metabolic/endocrine causes of tremor

•Gold standard - DaTscan (iodine-123-labelled ioflupane SPECT) - confirms loss of dopaminergic neurones; differentiates PD/atypical parkinsonism (reduced uptake) from essential tremor and drug-induced parkinsonism (normal uptake); performed 3-6 hours after injection

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In primary care: do NOT arrange a DaTscan and do NOT start treatment before specialist assessment. The GP's only role is to recognise the syndrome and refer URGENTLY to neurology.

Differential diagnosis

PD vs Essential tremor vs Drug-induced parkinsonism

Feature	Parkinson's disease	Essential tremor	Drug-induced
Tremor type	Resting, pill-rolling	Action/postural	Resting or mixed
Bradykinesia/rigidity	Present	Absent	Present
Onset	Asymmetric	Bilateral/symmetric	Symmetric
DaTscan	Abnormal	Normal	Normal
Treatment	Specialist-led, levodopa	Propranolol	Stop offending drug / procyclidine

Management

•GP action: refer URGENTLY to neurology (movement disorder specialist) - do not start medications in primary care

•First-line (specialist-initiated): co-careldopa (levodopa + carbidopa) - most effective symptomatic treatment; does NOT slow disease progression

•Psychosis in PD: reduce dopaminergic drugs first; if antipsychotic needed use quetiapine or clozapine only - never typical antipsychotics or risperidone

•Nausea in PD: domperidone preferred (peripheral D2 antagonism only); metoclopramide is contraindicated (crosses blood-brain barrier, worsens parkinsonism)

Complications

•Motor fluctuations - 'wearing off' and 'on-off' phenomena; consequence of long-term levodopa

•Peak-dose dyskinesia - involuntary writhing movements at peak levodopa levels

•Impulse control disorders - gambling, hypersexuality, binge eating; associated with dopamine agonist therapy

•Neuroleptic malignant syndrome - precipitated by abrupt withdrawal of anti-parkinsonian medication; never stop medications suddenly

•Aspiration pneumonia - bulbar involvement in later disease; leading cause of death

Drugs that worsen Parkinson's disease - avoid

Avoid in Parkinson's disease (dopamine antagonists / D2 blockers)

Metoclopramide - contraindicated antiemetic

Prochlorperazine - dopamine antagonist

Haloperidol - typical antipsychotic

Chlorpromazine - typical antipsychotic

Risperidone - high D2-affinity atypical antipsychotic

Lithium - worsens tremor

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Haloperidol and other typical antipsychotics block D2 receptors and can cause severe deterioration in PD motor symptoms and precipitate neuroleptic malignant syndrome. Never use in PD.