This is a progressive neurodegenerative disease of unknown cause though there is a genetic basis to a proportion of early onset cases and it is implausible that environmental factors are not relevant. The principal clinical features consist of bradykinesia (slowed movement), rigidity (muscle stiffness), tremor and loss of postural reflexes though other manifestations commonly complicate the course. It is commoner with advancing age, usually begins unilaterally, and the main structural pathological change is loss of neurones in the substantia nigra pars compacta with accompanying gliosis and Lewy Body formation. The main neurotransmitter deficit is loss of dopamine in the striatum, which causes increased striatal activity and ultimately the clinical features, via changes in function of both the indirect and direct pathways. Therefore, the treatment of the motor disorder is based on increasing dopamine levels in the brain through the use of L Dopa (which is turned into dopamine in neurones by decarboxylation, eg sinemet or madopar), dopamine agonists (which turn on dopamine receptors thus mimicking dopamine, eg permax, bromocriptine, ropinirole), or blocking the breakdown of dopamine by the enzyme Catchol-O-Methyltransferase (eg Tasmar).

In addition to medication, speech language therapy, occupational therapy and physiotherapy are all useful for individuals with Parkinson's Disease. Surgery is used occasionally, and this has included pallidotomy in the recent past although most centres are changing over to deep brain stimulation and several New Zealand patients have had stimulators inserted in Australia and are now being cared for by their movement disorder teams in this country.

The Parkinsonism Society in New Zealand, which has local branches throughout the country, employ field officers who can be of great assistance and support to those with Parkinson's or those caring for them. The Society sponsors educational sessions for professionals, caregivers, and patients and takes an active role in promoting awareness of Parkinson's Disease in the wider community. Main centres may have a Movement Disorder nurse specialist attached to the neurology department, and they can help coordinate appointment with various specialists including a psychiatrist familiar with the behavioural and emotional difficulties which can arise in Parkinson's Disease.

Emotional and cognitive changes are commonly seen. These are in part the result of changes in neurotransmitters other than dopamine such as serotonin (linked with depression and anxiety) and acetylcholine (linked with cognitive decline). There are also autonomic changes including altered bowel and bladder function, postural hypotension, sexual dysfunction and episodes of sweating. Some individuals experience significant pain or unpleasant sensations, especially in the legs.

Common neuropsychiatric aspects of or disorders which occur in Parkinson's Disease include Depression, Anxiety Disorders, Hallucinations, Sexual dysfunction, Dementia, Sleep Disorders, and personality change. These are mostly treatable and early identification and adequate management is important for maximising quality of life.

There is much written about the neuropsychiatry of Parkinson's Disease in the general neurology and general neuropsychiatry journals, but Movement Disorder is a useful specialised journal, which also includes videos of unusual presentations etc.