Idiopathic Parkinson's Disease (IPD) represents a specific degeneration of the dopaminergic pathway in the brain. The neurotransmitter predominates in the substantia nigra and the locus cerulus in the brain stem. The substantia nigra is a zone of pigmented neurons (dark as pointed out by the arrow) just beneath the cerebral peduncles. In this picture, the mid-brain on the right comes from a normal brain with fully pigmented substantia nigra. That on the left represents IPD with pale, depigmented substantia nigra.

Parkinsonism is a syndrome characterized by the clinical triad of tremor, rigidity and bradykinesia. IPD is only the commonest disease giving rise to Parkinsonism. Careful clinical and pathological examination is required to differentiate IPD from other neurodegenerative disease which can also give rise to Parkinsonism.