From the Guidelines
Parkinson's disease is diagnosed primarily through clinical evaluation, with key diagnostic features including resting tremor, bradykinesia, rigidity, and postural instability, as well as autonomic dysfunction, behavioral changes, and dementia 1. The clinical presentation of PD is characterized by these motor symptoms, which are related to progressive degeneration of the dopaminergic neurons in the substantia nigra projecting to the striatum.
- Key features include:
- Resting tremor
- Bradykinesia
- Rigidity
- Postural instability
- Autonomic dysfunction
- Behavioral changes
- Dementia The estimated interval between initial loss of dopaminergic neurons and the appearance of symptoms is approximately 5 years, after approximately 40% to 50% of the dopaminergic neurons in the substantia nigra have been lost 1. Imaging remains an essential diagnostic tool in the evaluation of a patient presenting with Parkinsonian symptoms, although it cannot confirm Parkinson's disease 1.
- Imaging modalities such as MRI or CT scans may be ordered to rule out other conditions, while DaTscan imaging can help support diagnosis in uncertain cases. A response to levodopa therapy often serves as a confirmatory diagnostic feature, with significant symptom improvement suggesting Parkinson's disease 1.
From the Research
Diagnostic Features of Parkinson's Disease
The diagnostic features of Parkinson's disease (PD) can be summarized as follows:
- The diagnosis of PD is predominantly clinical, based on a combination of the cardinal features of tremor, bradykinesia, and rigidity 2
- The clinical diagnosis of PD is based on the identification of some combination of the cardinal motor signs of bradykinesia, rigidity, tremor, and postural instability 3
- Rest tremor, bradykinesia, rigidity, and loss of postural reflexes are generally considered the cardinal signs of PD 4
- Other clinical features include secondary motor symptoms (eg, hypomimia, dysarthria, dysphagia, sialorrhoea, micrographia, shuffling gait, festination, freezing, dystonia, glabellar reflexes) and non-motor symptoms (eg, autonomic dysfunction, cognitive/neurobehavioral abnormalities, sleep disorders and sensory abnormalities such as anosmia, paresthesias and pain) 4
- A good response to dopaminergics is an important diagnostic criterion for PD 5
- Dopamine transporter single-photon emission computed tomography can improve the accuracy of diagnosis when the presence of parkinsonism is uncertain 6
Differential Diagnosis
The differential diagnosis of PD essentially lies between other conditions resulting in tremor, of which essential tremor is the commonest, and other akinetic-rigid syndromes, including:
- Progressive supranuclear palsy
- Multiple system atrophy
- Toxins and other degenerative disorders
- Diffuse Lewy body disease
- Corticobasal degeneration 2
- Subcortical vascular disease 5
Diagnostic Criteria
Three levels of diagnostic confidence are differentiated: Definite, Probable, and Possible, based on clinical criteria alone, with neuropathologic confirmation required for the diagnosis of Definite PD 3