Parkinson's disease

Parkinson's disease is a progressive neurological condition best known for its motor symptoms: tremor at rest, slow movement, rigid muscles, and difficulty with balance. As the disease progresses it also affects mood, sleep, autonomic function, and cognition.

It is the second most common neurodegenerative disease after Alzheimer's, and it usually appears in people over 60.

What goes wrong

Parkinson's is primarily a disease of the substantia nigra, a small region in the brainstem whose neurons produce dopamine. As these neurons die, the dopamine signal to the basal ganglia, which orchestrates voluntary movement, weakens. Motor symptoms appear when roughly 60 to 80 percent of these dopamine neurons are already gone.

The disease is also characterised by Lewy bodies, abnormal clumps of misfolded alpha-synuclein protein found inside affected neurons.

How it's diagnosed

Diagnosis is clinical. There is no definitive test in life. Useful supporting evidence includes:

• The characteristic combination of motor signs
• A clear response to dopamine replacement therapy (levodopa)
• Imaging: a DAT scan (a SPECT or PET scan that visualises dopamine transporter density) can support the diagnosis when uncertain
• MRI to exclude other causes (stroke, tumour, hydrocephalus)

Beyond movement

Many people with Parkinson's also experience:

• Sleep disorders, especially REM sleep behaviour disorder
• Depression and anxiety
• Loss of smell
• Constipation
• Cognitive decline, with up to 80 percent developing some form of dementia over the course of the disease

Treatment

Levodopa, the standard treatment for almost 60 years, replaces lost dopamine and reduces motor symptoms. Various adjunct medications, deep brain stimulation, and physical therapy all play a role.

Stem cell therapies that aim to replace lost dopamine neurons (such as the Bayer/BlueRock cell therapy, currently in trials) represent one of the most promising directions in the field.