Parkinson's disease
Progressive loss of dopaminergic neurons in the substantia nigra disinhibits the basal ganglia's motor-suppressing output, producing the triad of bradykinesia, rigidity and tremor because movement is constantly being over-restrained rather than driven.
In a nutshell
Loss of dopaminergic neurons in the substantia nigra removes the signal that normally permits movement, so the basal ganglia over-suppress it, producing bradykinesia, rigidity and resting tremor, asymmetric at onset, and responsive to dopamine replacement.
Classic presentation
An older adult with an asymmetric resting pill-rolling tremor, bradykinesia and rigidity, a shuffling gait and reduced facial expression, developing insidiously over months to years.
Key points
- Bradykinesia is the core feature required for diagnosis; tremor is not always present, but at least one of rigidity or tremor must accompany it.
- Asymmetric onset is typical of idiopathic Parkinson's disease; symmetrical onset or early falls, dementia or autonomic failure suggests an atypical parkinsonian syndrome instead.
- A clear, sustained response to levodopa supports the diagnosis; a poor response should prompt reconsideration.
- Non-motor features such as hyposmia, REM sleep behaviour disorder and constipation can predate the motor triad by years, reflecting early brainstem involvement.
- Treatment is symptomatic dopamine replacement; it does not halt neuronal loss, so efficacy and side effects such as motor fluctuations and dyskinesia evolve over time.
First-line investigation
Clinical diagnosis based on bradykinesia plus tremor and/or rigidity; DaTscan is reserved for diagnostic uncertainty.
First-line management
Specialist-initiated dopaminergic therapy, levodopa, a dopamine agonist or a MAO-B inhibitor, chosen according to age and symptom impact.
Exam traps
- Early falls, early dementia or early autonomic failure point away from idiopathic Parkinson's disease towards an atypical parkinsonism such as PSP, MSA or dementia with Lewy bodies.
- A symmetrical tremor that is worse with action, not at rest, and improves with alcohol suggests essential tremor, not Parkinson's disease.
- Drug-induced parkinsonism, from antipsychotics or metoclopramide for example, is typically symmetrical and reversible: always check the drug history.
Educational content pending clinical review. Not medical advice.