Monday, 13 February 2017

Parkinson's Disease

Parkinson's is a relatively common disease, with one in every 500 people in the United Kingdom suffering from the condition. The symptoms are mainly motor-related unlike Alzheimer's which affects mostly cognitive functions. Patients with Parkinson's  tend to suffer from rigidity or stiffness, slowness in movement (bradykensia) and tremors. However symptoms such as depression, insomnia and some loss of cognitive abilities can also be found in sufferers of Parkinson's. In most sufferers the symptoms of the disease are evident when they are over the age of 50, but 1 in 20 develop symptoms when they are under 40. 

In the middle of the brain lies a small area called the substantia nigra. In Parkinson's the nerve cells here are lost which cause the motor-related symptoms associated with the disease. The cells in this region of the brain produce dopamine, a neurotransmitter essential for the transfer of electrical signals involved in coordinating movement. Since the end product of dopamine is melanin, the substantia nigra is significantly darker in healthy individuals than the rest of the brain and Parkinson's patients, who have damaged cells in these region, have lighter coloured substantia nigra as result.

The Substantia nigra in Parkinson's sufferers compared to healthy individuals
As both Parkinson's disease and Lewy Body disease involve the protein alpha-synuclein, it makes it difficult to differentiate between the two diseases. In both, lewy Bodies form as result of alpha-synuclein clumping and forming aggregate plaques in neurons. However a sufferer is considered to have Parkinson's if their motor-related symptoms appear at least a year before dementia, whereas in Lewy Body disease both symptoms appear at the same time.

Unlike most neurological conditions, Parkinson's can be diagnosed without a CT or MRI scan. Signs of tremor, stiffness and slowness of movement are in many cases a clear sign of Parkinson's Disease. However, a single-photon emission computerised tomography (SPECT) scan can also be used for diagnosis. It uses a radioactive trace that is injected inside the body to analyse the blood flow through regions of the brain, highlighting areas where blood flow is limited due to injury. This trace emits gamma rays that are detected by the scanner to form 2D cross sections that are pieced together to form a 3D image.There is some exposure to radiation from the tracer however there are no associated long-term health risks.
SPECT scan comparing the brain of a Parkinson's sufferer with a healthy individual
(Wikidotcom, 2017)
Parkinson's disease can be treated with a drug called levodopa. In fact, if a patient responds positively to the drug and there are signs of improvement then it further certifies that they are suffering from the disease. Like mentioned before, Parkinson's sufferers are unable to produce sufficient dopamine and the injected chemical cannot pass through the blood-brain barrier to be used in the brain. Levodopa is used instead. It is absorbed and converted by an enzyme called dopa-decarboxylase into dopamine in the brain, and consequently increasing dopamine levels to normal. This has proven to be the most effective form of medication for Parkinson's sufferers at the moment. Levodopa can be partnered with another drug called carbidopa that prevents Levodopa from being converted by the body too early before it has reached the brain. However, the use of levodopa is only a form of treatment for the Parkinson's disease as a cure is still yet to be found. 
How Levodopa is absorbed and used in the brain
(Brain: the inside story, 2014)

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