Parkinson's disease
Diagnosis
Because no diagnostic tests have been developed to distinguish PD from other forms of parkinsonism, PD remains a clinical diagnosis, based on the clinician's ability to recognize its characteristic signs and associated symptoms, especially in the early stages. An accurate clinical diagnosis is fundamental to the expectation that pharmacotherapy of PD will be effective. In general, the other forms of parkinsonism respond poorly to antiparkinson drugs. [1]
DaTscan
Striatal dopamine transporter imaging using 123I-FP-CIT single-photon emission computed tomography (DaTscan) can reliably distinguish patients with PD and other parkinsonian syndromes associated with nigrostriatal degeneration (ie, MSA, PSP, and corticobasal degeneration [CBD]) from controls or patients with essential tremor (ET), but it cannot differentiate PD and the other parkinsonian syndromes from one another. The available evidence suggests that the overall accuracy of DaTscan for parkinsonian syndromes is equal to but not better than the accuracy of a carefully obtained clinical diagnosis. If one assumes that the detection of a striatal dopamine deficiency by DaTscan is the diagnostic gold standard for parkinsonian syndromes, then the sensitivity of the clinical diagnosis is high in both early and advanced PD. However, the specificity varies with the duration of the illness; the clinical diagnosis in advanced PD has a high specificity, while the clinical diagnosis in early PD has a specificity of only 67 percent. [1]
Based upon data and expert clinical experience, use of DaTscan is suggested for the following scenarios: [1]
- Patients for whom the diagnosis is unclear after serial clinical evaluations, such as those with long-standing ET whose tremor evolves to have characteristics of PD but fails to respond unequivocally to levodopa
- Patients suspected of having drug-induced parkinsonism (striatal uptake of the isotope should be normal in this setting)
