As our knowledge of Parkinson's disease and parkinsonism increases considerable confusion can arise in relation to the terms used to describe these conditions. To maintain consistency in the text the following definitions will be used.

Parkinsonism

A clinical syndrome of akinesia accompanied by rigidity and often tremor. Akinesia includes difficulty with voluntary motor actions, difficulty performing sequential or concurrent motor actions, slowness of voluntary movement, and abnormal fatigability of repetitive motor actions. Rigidity, or ‘stiffness’, can be defined as the resistance encountered by an examiner when passively stretching relaxed muscles around a joint. Rigidity in parkinsonism can often be detected in the axial skeleton and upper limbs by the examiner performing passive flexion/extension movements of the neck and wrist joint. Tremor is often present at rest when the muscles are fully relaxed and is usually first noted in the upper limb involving the hand and fingers. Leg and jaw tremor may less commonly occur. Parkinson's disease is the most common cause of parkinsonism and arises sporadically and is of unknown cause. Known causes of parkinsonism include drugs, cerebrovascular disease, other sporadic and inherited neurodegenerative disease, infections, head trauma, hydrocephalus, and metabolic diseases, amongst others.

Parkinson's disease (PD)

Levodopa-responsive parkinsonism resulting in a characteristic clinical picture and natural history. When present, a typical ‘pill rolling’ tremor involving the thumb and index finger is almost pathognomic for PD or drug-induced parkinsonism. The primary neuropathological findings consist of degeneration of cells in the substantia nigra pars compacta resulting in striatal dopamine deficiency and the presence in surviving cells of inclusions called Lewy bodies.