Parkinson's disease: definition, symptoms, causes and treatments

Parkinson's disease is a neurodegenerative disorder characterised by the destruction of dopamine neurons. Patients suffer from motor symptoms such as akinesia or tremors, as well as non-motor symptoms such as cognitive impairment. There is no cure for the disease, but some symptoms can be alleviated with medication. Numerous studies are underway to improve management of the disease and slow degeneration.

What is Parkinson's disease?

Parkinson's disease is a degenerative disorder, very rare before the age of 45, affecting 1% of the population over the age of 65, and affecting both men and women. The fundamental lesion is the degeneration of a certain type of neuron: the dopaminergic neurons located in the substantia nigra of the brain.

These neurons produce dopamine, one of the nervous system's neurotransmitters. It is particularly involved in the neurons responsible for controlling body movements. In Parkinson's disease, there is a deficit of dopamine in the brain, which manifests itself in movement disorders.

This rapidly affects the lives of patients: walking, sitting down, getting dressed or even getting up becomes difficult.

The causes and risk factors of Parkinson's disease

The cause of Parkinson's disease is unknown. Very rare cases are hereditary, and in these cases Parkinson's disease occurs in very young patients. A genetic variant is also suspected in Parkinson's disease, particularly in its rare forms, and in patients affected at an early age, i.e. before the age of 60. Around ten genes are thought to be involved in the development of the disease, but it is not known where the mutations occur or what impact they have, although research is progressing.

Similarly, no risk factor is known with certainty. Only the role of exposure to pesticides is now well established. Doubts remain as to the real influence of the following factors:

Age;
Metals (lead, manganese and mercury, iron, copper, cobalt, etc.);
Organic solvents and non-metallic toxins (industrial toxins, carbon monoxide, cyanide, exhaust fumes, glue, paint, lacquers, etc.);
Head injuries;
Constipation;
A diet low in antioxidants (and high in ions);
Diabetes;
Certain viral infections (chickenpox, measles, German measles, mumps, etc.).

Taking neuroleptics (psychotropic drugs used to treat various psychiatric disorders) and certain psychological situations, such as depression or stress, may also increase the risk of developing Parkinson's disease.

The symptoms of Parkinson's disease

The onset of the disease is insidious and progresses slowly: reduced activity, abnormal tiredness, poorly localised pain, difficulty writing, trembling in one hand, fluctuating stiffness, etc.

Gradually, the other signs of Parkinson's disease appear, with the three motor symptoms that characterise the disease, also known as the Parkinsonian triad: akinesia (slowness of movement), hypertonia (rigidity) and resting tremor. Dyskinesias (rapid, restless involuntary movements) may also occur.

Sometimes, certain movements are very easy to carry out (on)... and at other times, they are carried out with great difficulty (off). This is the "on-off" effect, a very destabilising period for the patient's physical and mental health. Nevertheless, the third phase of the disease - which occurs when the treatment is no longer effective - remains the most disabling because the symptoms become more pronounced.

Akinesia (or slowed movement)

Akinesia is defined by the infrequency, difficulty of initiation and slowness of movement. It affects walking in particular: it is difficult to get started, sometimes by stamping on the spot, then taking small steps, with the feet "stuck" to the ground, the arms motionless and no longer swinging, the back bent forward and the neck stiff. The start is sometimes paradoxically facilitated by the presence of an obstacle in front of the patient. Sometimes the blockage occurs after starting, with the patient coming to a sudden halt, suddenly unable to move forward, his feet glued to the floor: this is the phenomenon of kinetic jamming. Akinesia is often noticed early on during writing, which becomes more difficult and smaller in size (known as micrographia). The face is also affected, with fixed, barely expressive features and a fixed gaze. Speech is sparse, slurred and monotonous. All gestures, including the person's voice, are rare and slow. Akinesia is therefore responsible for a loss of automatic, unconscious movements: the patient must consciously command most of his or her movements, even those that are normally performed without a thought.

Hypertonia (or muscular rigidity)

Hypertonia is known as extrapyramidal hypertonia. It is a rigidity, a stiffness of the limbs and the axis (the spine), which is observed when the patient's joints are moved, and the patient is asked to be as passive and relaxed as possible. An involuntary resistance to movement is then observed (e.g. flexion-extension of the wrist), which disappears and reappears in successive jerks during the movement: this is the so-called cogwheel phenomenon. This rigidity tends to fix the person's limbs in the position imposed on them. The movement is no longer fluid but jerky. However, muscular rigidity is not due to a lack of muscular activity but, on the contrary, to an exaggeration of muscle tone.

Tremors at rest

Tremor is common in people with Parkinson's disease. It is a regular tremor, typically appearing at rest, and disappearing during movement; it is sometimes present when maintaining an attitude (for example when the patient holds his arms out in front of him). It disappears during sleep and increases during emotions or efforts at concentration such as mental arithmetic. In the hands, it resembles the crumbling of bread between the fingers. It can affect the face, with a trembling of the lips or chin.

Decreased postural reflexes

Balance problems appear later than the other signs. Decreased postural reflexes are responsible for balance problems. It usually only appears in patients after several years. It is responsible for falls, typically backwards, as the patient loses the reflex to 'catch' himself if he becomes unbalanced.

Other disorders associated with Parkinson's disease

Other disorders are often associated with Parkinson's disease:

Pain, often in the form of cramps or unpleasant pins and needles;
Digestive problems (constipation) or urinary problems (urinary urgency);
Orthostatic hypotension (a drop in blood pressure when the patient stands up, leading to dizziness or even falls);
Sleep disorders (insomnia, drowsiness);
Sweating, hot flushes, excessive salivation;
Mental disorders are fairly common during the course of the disease: depression, anxiety, sometimes irritability or ideas of persecution.
Cognitive problems are common after the disease has progressed for years.

However, intellectual impairment is rare, and other diagnoses should be considered. Visual hallucinations sometimes occur, but almost always after many years or under certain treatments, otherwise other diagnoses should be considered.

Parkinson's disease: how is it diagnosed?

Parkinson's disease develops gradually and silently. It is therefore often several years before the symptoms become bothersome, prompting the patient to talk to his or her doctor.

Diagnosis is based on a description of the symptoms (the doctor usually looks for two or more of the main symptoms, which are slowness of movement, stiffness or tremors) and a clinical examination by the health professional.

Once Parkinson's disease has been diagnosed, treatment is started.

Parkinson's disease: additional tests and analyses

Additional tests are normal in Parkinson's disease, and none are essential. However, a brain scan or MRI is most often carried out to look for other diseases; other tests are sometimes carried out if all the signs of the clinical examination or the course of the disease are not absolutely typical of Parkinson's disease: lumbar puncture, electroencephalogram, blood tests.

An electrocardiogram is performed to check for contraindications to certain anti-parkinsonian treatments; a urodynamic work-up is performed if there are clear urinary disorders, in order to specify the type of disorders and adapt treatment as best as possible.

The course of the disease

Parkinson's disease is a chronic illness, which can be largely improved but not cured by treatment. Initially, the disorders are generally discreet, not always requiring treatment. The onset of treatment is almost always accompanied by a significant improvement or even disappearance of the signs of the disease. This period of great efficacy, sometimes called the "honeymoon period", usually lasts several years.

After this period, which is more or less prolonged, the effectiveness of the treatment diminishes; the dosage of the medication must then be increased, which exposes the patient to undesirable effects; in addition, the response to the treatment changes and fluctuations appear (the symptoms worsen and then diminish or even disappear several times during the day), as well as abnormal movements such as dyskinesias (rapid uncontrolled movements of certain parts of the body), dystonia (stiffness of certain parts of the body), or periods when the body is blocked: this is the stage of motor complications. It is then necessary to increase the doses, increase the frequency of drug intake, combine several drugs or even other treatments.

Treatments for Parkinson's disease

There is no cure for the disease. However, there are drugs that can compensate for the dopamine deficiency and thus reduce certain symptoms.

Anti-Parkinson drugs that mimic the effects of dopamine;
Drugs that inhibit the enzymes that break down dopamine;
Deep brain stimulation: reserved for people with a significant disability linked to motor fluctuations or dyskinesias, and who are able to withstand the procedure (under 70 years of age);
Administration of apomorphine via a subcutaneous pump or continuous L-dopa via a gastric tube;
Physiotherapy to improve walking;
Speech therapy to improve swallowing and speech disorders.

Not to be confused with...

Parkinson's disease is distinguished from other Parkinsonian syndromes, which have the same symptoms (known as extrapyramidal symptoms) but which do not have the same cause or the same course; in particular : the use of neuroleptics or certain other drugs; repeated cerebrovascular accidents (strokes), known as "lacunar states"; other degenerative neurological diseases that are rarer than Parkinson's disease (multi-system atrophy, diffuse Lewy body disease) ; hydrocephalus (excess cerebrospinal fluid in the brain); disorders of copper and iron metabolism; certain types of manganese, cobalt, mercury and carbon monoxide poisoning; repeated head trauma (boxer syndrome); certain brain tumours (very rare).