Parkinson's Disease
Parkinson's disease [54, 79, 187] was first described in 1817 by the English physician James Parkinson [74], after whom it is named. It is a neurodegenerative disorder of the central nervous system characterized by progressive, primarily motor disturbances. Its causes are poorly understood.
The clinical picture of this disease is the consequence of neuron loss in the locus niger [38] and impairment of the nigrostriatal tracts [31]. The disease usually begins between the ages of 45 and 70 [74]. It is the second most common neurodegenerative disease [79, 91] after Alzheimer's disease.
Parkinson's disease is distinguished from Parkinsonian syndromes [191], which arise from various origins, are generally more severe, and respond inconsistently to treatment.
Pathophysiology :
It is a neurodegenerative condition characterized by the premature death of neurons, essentially those in the substantia nigra (locus niger) [187]. This part of the brain, located at the midbrain-diencephalon junction, is involved in movement control, partly through the secretion of a neurotransmitter: dopamine [41].
The loss of dopaminergic neurons results in an insufficient quantity of dopamine within the striatum; the progressive nature of the disease explains why it remains undetected for many years. Initial clinical signs only appear after the destruction of approximately 70% of the neurons [192] in the locus niger.
Over time, other neural structures may be affected, involving other neurotransmitters responsible for controlling other faculties such as memory, emotions, balance, blood pressure, sphincters, and sexuality [191].
Diagnosis :
The symptoms of Parkinson's disease are diverse. They are not always highly specific, and the disease may begin with vague disturbances such as peri-articular pain, depression, or fatigue. At the onset of the disease, symptoms are characterized by their unilateral nature [79, 91]. These symptoms include:
- Tremors [69]: These manifest primarily at rest, persist even during sleep, and worsen with emotion. They mainly affect the upper limbs, particularly the hands; the head does not shake. They often cause social embarrassment but rarely result in major disability.
- Akinesia [185]: Difficulty initiating or continuing a movement, and the loss of automatic movements.
- Body rigidity [187]: Excessive muscle tension results in permanent stiffness, increased resistance to movement, a short-stepped gait, falls, loss of balance, and forward curvature of the spine.
- Loss of facial expression: The face becomes inexpressive.
Treatment :
The treatment of Parkinson's disease has seen considerable progress in recent years.
Medications :
No drug has demonstrated efficacy in stopping the progression of Parkinson's disease [193, 194]; there is no curative treatment. Current medicinal protocols remain purely symptomatic [96].
Levodopa or L-dopa [187] is a dopamine precursor used therapeutically because dopamine itself does not cross the blood-brain barrier [1, 41]. L-dopa provides symptomatic relief for many patients. It is converted into dopamine in the brain to meet the needs of regions lacking it. However, after several years of treatment, Levodopa gradually becomes less effective [31].
Other drugs may be administered alone or alongside L-dopa: dopamine agonists [79], enzymes that inhibit dopamine degradation [178], or enzymes that inhibit the breakdown of Levodopa in the blood. Other treatments may be administered to reduce tremors, such as anticholinergic medications [185], which are prescribed alone or in combination with the previously mentioned treatments.
Certain symptoms, such as loss of balance, drops in blood pressure, mood disorders, or memory impairment, respond poorly to antiparkinsonian drugs because they are caused by damage to other brain circuits that do not involve dopamine, thus requiring other types of medication.
Deep brain stimulation :
When medications no longer provide the expected benefits, it is possible for certain patients to have electrodes implanted in specific brain regions, connected to a stimulator (pacemaker), to improve the functioning of the damaged areas [69].
Physical rehabilitation :
Alongside drug treatments, physical rehabilitation (physiotherapy [193], occupational therapy [191] , and speech therapy [195] ) is an indispensable complement. It helps maintain the flexibility necessary to pursue motor activities.