What is Parkinson's Disease?

PD mainly affects middle-aged and elderly people, with only 15% of all PD diagnosis happening before the age of 40

PD mainly affects middle-aged and elderly people, with only 15% of all PD diagnosis happening before the age of 40

Parkinson’s disease affects more than 10 million people worldwide, and although it is a horrible, debilitating disease that will stay with you all your life, it is not deadly at all. But what makes Parkinson’s stand out from other diseases, are its strange symptoms, of tremors, muscle rigidity or even hallucinations.

But before we start with all of the symptoms, let's understand what Parkinson’s disease (PD) really is. Parkinson’s disease is a “progressive degenerative (gets worse over time) disease of the nervous system, marked by tremor, muscular rigidity and slow imprecise movements”. PD mainly affects middle-aged and elderly people, with only 15% of all PD diagnosis happening before the age of 40.

But although Parkinson’s chiefly affects the elderly, there are some rare cases where younger people are diagnosed with the disease. A notable example of this is Michael J Fox (Back to the future), who was diagnosed at the age of 29. Finally, another observation is that men are often more affected than women, and people from an African-American descent are least likely to get the disease (although we still don’t know why).

Parkinson’s disease is characterized by tremor (mainly), slowed movement (bradykinesia), balance difficulties and stiffness in limbs, just to name a few. These symptoms all seem to have one thing in common, they all affect our motor functions. And although there are some non-motor symptoms such as confusion, hallucinations, and delusions, these are rarer, and only found in cases of patients with a late stage of PD.

There are many different ‘pathways’ that dopamine can take between different neurons in our brains.

There are many different ‘pathways’ that dopamine can take between different neurons in our brains.

But what is the cause of these symptoms, and what happens in your brain? The root cause of the symptoms is the destruction of cells of a specific part of the brain (parts of the basal ganglia) that control movement. But what drew me to write about this topic, is the fact that all of these brain cells that are destroyed use the neurotransmitter dopamine to relay the information about the movement. I have covered dopamine quite extensively in my past articles, and it came as a surprise to me that dopamine was involved in so much more than just pleasure and reward circuits.

Let me explain. Dopamine is a neurotransmitter, which means that it is a chemical messenger that is used to relay information between neurons, muscles or gland cells. And there are many different ‘pathways’ that dopamine can take between different neurons in our brains. These pathways are associated with different functions such as the reward function of our brain (mesolimbic pathway), hormone secretion (tuberoinfundibular pathway) or finally the motor function pathway (nigrostriatal pathway), which also controls some parts of reward-related cognition (reward function).

The cells that are destroyed are chiefly from the motor-related circuit. This is why people that suffer from PD have issues with motor aspects, and not emotional aspects that characterize dopamine deficiency in general.  But the symptoms of PD don’t appear until a staggering 80% of those cells have been destroyed.

When the cells that secrete dopamine die, there is much less dopamine to carry the messages to each motor unit in our muscles, and as a result, the motor unit drops out. When we move our hand, for example, it may seem smooth, but it is the action of many motor units working together, giving the illusion that it is smooth. So, when many muscle units drop out, there are gaps between the motor units moving, causing a tremor. (see my previous article about tremors).

Diagram of a Motor Neuron

Diagram of a Motor Neuron

But although scientists have pinpointed what causes the symptoms, it is still unknown as to why the degeneration happens in the first place (some exceptions), and why it affects black people less, for example. This type of PD is called idiopathic parkinsonism (don’t know the cause). The ‘exceptions’ as mentioned before, include vascular parkinsonism, which tends to occur in older people that suffer from diabetes.

This type of PD occurs, when there is a limited amount of blood supply to the brain, or even if a person has had a mild stroke, this kills off the cells in the basal ganglia, causing the same symptoms as idiopathic parkinsonism. The final exception is ‘drug-induced parkinsonism, which only affects 7% of all PD patients. This type of parkinsonism is generally caused by neuroleptic drugs which block the action of dopamine, and in some cases recreational drugs such as cocaine (see later). But the biggest difference here, is that most patients recover within days or months after stopping taking the drug, and the symptoms are not as severe, for example, no arm swinging was observed with patients with drug-induced parkinsonism.

Specifically, in recreational drug use, there is some evidence to show that cocaine and synthetic drugs can cause drug-induced parkinsonism, in their different ways. In the case of synthetic drugs, a study was conducted in the 1970’s where users took synthetic drugs as a cheap alternative to cocaine.

The drug contained a chemical called MPTP which (after a post-mortem examination of an overdose patient), showed that it caused great damage to the basal ganglia. But for cocaine, when a tolerance is developed, there is less dopamine produced (or received) in the brain, and although it has not been directly proved, the statistics show that cocaine users are very likely to develop PD. In both cases, when PD drugs were administered, there were signs of improvement, which almost definitely means that the person has PD.

On the topic of treatments for PD, the main ones at the moment include Drugs, Therapy, and surgery. The drugs given to patients are called dopamine agonists. These drugs increase the amount of dopamine in your brain (cocaine is an example of a dopamine agonist for example). The main drug used in the USA is called Cabaser, but seeing as Cabaser gives out dopamine in your brain, it could result in dependence on the drug. But since the dopamine produced to target the motor pathway, there is little dependence.

Though with a similar dopamine agonist produced by GlaxoSmithKline (GSK), there was a side effect of dependence on gambling and sex, which could only be linked to the increase in dopamine production, although this is quite rare. Nevertheless, in France, GSK paid out $256,927 to a French man who claimed that he was ‘not made aware of these symptoms’ because he developed a serious gambling addiction.

The therapy used, is not as effective as the drugs in controlling the symptoms, and are not as widely used as drugs. And in an even smaller minority, surgery is used (where the drugs are not effective on the patient), this surgery is called DBS (deep brain stimulation), where the parts of the brain that is responsible for motor functions, are stimulated by electricity, by a small device implanted into the brain.

Albeit Parkinson’s disease does not cause death, it can be really distressing for the patients to go through the symptoms, especially since the disease is degenerative, and the cells will keep on dying, until there are none left, resulting in all the muscles frozen in some cases. Thus, rendering the patient confined to a wheelchair.