Parkinsons disease

All About Parkinson's Disease

All About Parkinson's Disease

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all are absent at rest and more pronounced on voluntary movement.

DIAGNOSIS

When tremor, rigidity and bradykinesia coexist, distinguish Parkinson' disease from secondary parkinsonism by the absence of a relevant drug history. Distinguish TREMOR from

- senile tremor

- essential tremor

- metabolic tremor

Distinguish RIGIDITY from spasticity - with passive limb movement, spasticity is felt towards the end rather than through the full range of movement.

Distinguish BRADYKINESIA from - gait disturbance of normal pressure hydrocephalus. SPECT imaging with 123I-iodobenzamide (IB2M) as a D2 ligand and PET studies with [18p] 6 fluorodopa appear promising diagnostic tests. Pharmacologic tests of dopaminergic responsiveness with apomorphine (Di and D2 receptor agonist) do not give definite diagnostic information.

TREATMENT is symptomatic and does not halt the pathological process. It aims at restoring the dopamine/acetylcholine balance (dopamine deficiency) by:

1. Anticholinergic drugs

Synthetic anticholinergics, e.g. benzhexol - useful in control of tremor, but effect on rigidity and bradykinesia is often minimal.

Side effects: dry mouth, blurred vision, urinary retention and confusion.

2. Increase dopamine

Nerve * terminal

1. Exogenous dopa

Postsynaptic receptor

1. Exogenous dopa

— 2. Dopamine agonist which mimics dopamine at the postsynaptic striatal receptor site

Exogenous dopa w

Postsynaptic receptor

Given as 1 — levodopa, or 2 — levodopa + decarboxylase inhibitor, which prevents peripheral breakdown in the liver allowing a higher concentration of dopa to reach the blood-brain barrier; also the peripheral side effects (nausea, vomiting, hypotension) arc diminished. Central side effects: confusion, depression, dyskinetic movements and following long-term treatment - 'OnjOff phenomenon (see later).

Controlled-release or long acting preparations produce constant plasma levels and a more even clinical response.

Exogenous dopa improves bradykinesia, rigidity and, to a lesser extent, tremor, but in 20% the response is poor. 'Good' responders often develop central side effects later -especially the 'on/off phenomenon.

Exogenous dopa

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