Parkinson’s disease (PD) is a degenerative disorder of the central nervous system. The motor symptoms of Parkinson’s disease result from the death of dopamine-generating cells in the substantia nigra, a region of the midbrain; the cause of this cell death is unknown. Early in the course of the disease, the most obvious symptoms are movement-related; these include shaking, rigidity, slowness of movement and difficulty with walking and gait. Later, cognitive and behavioral problems may arise, with dementia commonly occurring in the advanced stages of the disease. Other symptoms include sensory, sleep and emotional problems.
Parkinson’s disease is often defined as a ‘Parkinsonian syndrome’ that is idiopathic (having no known cause), although some atypical cases have a genetic origin.
The progression of Parkinson’s disease and the degree of impairment vary from individual to individual. Many people with Parkinson’s disease live long productive lives, whereas others become disabled much more quickly. Premature death is usually due to complications such as falling-related injuries or pneumonia.
Parkinson’s disease is a heterogeneous and genetically complex disorder of largely unknown etiology. It is the second most common neurodegenerative disease in the general population. Approximately four million people worldwide are estimated to be living with Parkinson’s disease. Incidence of Parkinson’s increases with age, but an estimated four percent of people with PD are diagnosed before the age of 50. Adult-onset Parkinson’s disease is most common, but early-onset Parkinson’s disease (onset between 21-40 years), and juvenile-onset Parkinson’s disease (onset before age 21) also exist.
Modern treatments are effective at managing the early motor symptoms of the disease, mainly through the use of levodopa and dopamine agonists. As the disease progresses and dopaminergic neurons continue to be lost, these drugs eventually become ineffective at treating the symptoms and at the same time produce a complication called dyskinesia, marked by involuntary writhing movements. Diet and some forms of rehabilitation have shown some effectiveness at alleviating symptoms. Surgery and deep brain stimulation have been used to reduce motor symptoms as a last resort in severe cases where drugs are ineffective.
The term Parkinsonism is used for a motor syndrome whose main symptoms are tremor at rest, stiffness, slowing of movement and postural instability. The main motor symptoms are collectively called “Parkinsonism” or “Parkinsonian syndrome”. Parkinsonian syndromes can be divided into four subtypes according to their origin:
- Primary or idiopathic
- Secondary or acquired,
- Hereditary Parkinsonism
- Parkinson plus syndromes or multiple system degeneration
Parkinson’s disease is the most common form of Parkinsonism and is usually defined as “primary” Parkinsonism, meaning parkinsonism with no external identifiable cause.