There are no specific diagnostic tests to detect Parkinson's disease. The diagnosis is usually made after a clinical analysis by the neurologist.
The diagnostic criteria for this disease have been defined by the UK Brain Bank. Parkinson's disease is diagnosed if the patient has akinesia (motor initiation disorder) and at least one of the following two symptoms :
Resting tremors, of low amplitude and disappearing during a voluntary movement
Rigidity of the limbs or hypertonia. When the neurologist flex and extend the limb, it will resist and moves with "jerky" motions. This is called the "cogwheel" phenomenon.
It is important to note that these motor symptoms appear when about 80% of the dopaminergic neurons have been affected in the substantia nigra.
Confirm the diagnosis
The diagnosis of the disease can be confirmed by some specific characteristics:
Early symptoms of the disease: loss of olfaction, constipation...
Good response to dopaminergic treatment
If there is any clinical doubt, the neurologist may request an MRI or DAT-SCAN.
MRI allows an anatomical analysis and detects a degeneration of the dopaminergic neurons of the substantia nigra, resulting in a depigmentation of the area.
The DAT-SCAN (dopaminergic transporter) allows a functional analysis and, by injecting a radioactive agent, detects the activity of dopaminergic transporters. A decrease in the activity of these transporters will confirm the diagnosis.
Is it possible to misdiagnose ?
There are many conditions with symptoms similar to idiopathic Parkinson's disease. This is called "differential diagnosis". The following disorders should be considered in the diagnosis:
Parkinsonian syndromes due to neuroleptics. One of the first hypotheses to consider when the characteristic symptoms of the disease are detected. Neuroleptics will block dopamine receptors and can sometimes cause akinesia or hypertonia.
"Parkinson-plus" syndromes. These syndromes include progressive supranuclear palsy (PSP), multisystematic atrophy (MSA), cortico-basal degeneration (CBD) or dementia with Lewy bodies. These syndromes generally respond poorly to dopaminergic treatment and present a more rapid and pronounced evolution compared to Parkinson's disease.
Essential tremor. It is sometimes difficult to differentiate between tremor caused by Parkinson's disease and essential tremor. Essential tremor is usually bilateral (not unilateral as in PD) and will be less intense when the limbs are at rest.
Today, the diagnosis of Parkinson's disease is based mainly on clinical observations. Current studies aim to develop new diagnostic tests based on the early detection of biomarkers. An early diagnosis of Parkinson's disease allows the rapid implementation of an adapted treatment and limits the progression of neurodegeneration as early as possible.