Understanding Parkinson's disease

Parkinson’s disease is a chronic and progressive neurodegenerative movement disorder which effects 1% of people over 60 and the most common onset is between ages 65-70. It is more common in men than women. Many cases appear to be sporadic, however genetic factors are thought to contribute to 5-10% of cases. Environment can also play a role, such as head injury, cigarette smoking, alcohol use and vitamin D levels, however the actual cause of the disease is still not fully understood.

Parkinson’s disease is characterised by three main hallmarks of tremor, rigidity, and slow movement. It involves motor and non-motor symptoms. Many of the classic motor symptoms can present in an asymmetrical manner, including a ‘pill rolling’ tremor at rest in the hands or fingers. Other symptoms include a ‘cog-wheel’ form of rigidity in the limbs, which also impacts the trunk and contributes to a flexed, stooped posture, and an overall slowing of movement, which can include a ‘mask’ like face with limited expression and eye blinking. Patients may present with slow writing which becomes progressively smaller known as micrographia, and a stiff, short, shuffling gait with reduced arm swing, frequent freezing and trouble initiating again once stopped.

A fourth feature of postural instability is sometimes included, although this generally presents late in the disease progression. Other non-motor features include a decreased sense or loss of smell, constipation, REM sleep behavioural disorder where a patient physically acts out dreams with talking and uncontrolled arm and leg movements, plus postural hypotension, slow thought processes, dementia, psychosis, particularly visual hallucinations, as well as somnolence and fatigue. Dizziness and falls are typical of patients with advancing Parkinson’s disease and may be related to postural hypotension, a form of severe low blood pressure, and are also a side effect of dopaminergic medications.

No specific medical imaging tests exist to diagnose Parkinson’s disease. Imaging test such as MRI can help to rule out other disorders. A SPECT dopamine transporter scan can help to support a diagnosis, but ultimately diagnosis is made on the basis a of a patient’s neurological presentation.

The pathophysiology of Parkinson’s disease involves degeneration of the pigmented neurons in a part of the midbrain, called the substantia nigra. The subsequent loss of substantia nigra neurons results in depletion of dopamine. This occurs in the dorsal aspect of the putamen, which is a part of the basal ganglia. Projections from the substantia nigra to the basal ganglia facilitate smooth movement via the nigro-striatial pathway. As Parkinson’s disease progresses, Lewy Bodies develop when ⍺-synuclein proteins become tangled and accumulate within the brain, forming inclusions within the cells. If these are unable to be removed, they become toxic. Lewy body spread often closely relates to the degree of clinical progression and is outlined in Braak staging. The Lewy bodies continue to spread throughout the brain, and overtime ascend to the medulla and pontine tegmentum followed by the midbrain, basal forebrain and finally the neocortex.   

Medications for Parkinson’s disease increases levels of the neurotransmitter dopamine and block cholinergic receptors. They act to increases dopamine in the brain and peripheral tissues to assist in the replenishment of depleted striatal dopamine, helping to control some of the movement symptoms of Parkinson’s disease. Unfortunately, the medications used to treat Parkinson’s disease cause significant side effects and are unable to reverse the dopaminergic neuron loss. As the disease progresses, surgical options may be considered, including deep brain stimulation.

If you are concerned about someone you know, consult your GP, who will then refer the patient to a specialist for a definitive diagnosis. These days, a multidisciplinary health care team will be involved, allowing for holistic treatment of Parkinson’s disease. The team may include a neurologist, physiotherapist, occupational therapist, nurse, pharmacist, social worker, general practitioner, psychiatrist, dietitian and geriatrician. The team will work closely together to ensure a person living with Parkinson’s disease has the best outlook and quality of life possible.