How specific is the clinical diagnosis of Parkinsons Disease?
In one clinical pathological study using the data from the Arizona Study of Aging and Neurodegenerative Disorders, only 80 of 97 (82%) cases diagnosed at first visit with probable PD had neuropathologically confirmed Parkinsons Disease (Adler et al., 2014).
Furthermore, only 8 of 15 (53%) diagnosed with probable Parkinsons Disease with less than 5 years of disease duration had the diagnosis confirmed at autopsy, whereas 72 of 82 (88%) with ≥5 years of disease duration had pathologically confirmed Parkinsons Disease.
Thus, clinical diagnosis of Parkinsons Disease identifies patients who will have pathologically confirmed Parkinsons Disease with a sensitivity of 88% and specificity of 68%.
Although the presence of rest tremor, bradykinesia, and rigidity has been thought in the past to be highly predictive of the correct diagnosis, this study found that response to dopaminergic drugs and levodopa-related motor complications were most helpful in making an accurate diagnosis of Parkinsons Disease.
Furthermore, only 20% to 26% of untreated cases who would be considered candidates for drug trials had accurate diagnosis of Parkinsons Disease.
These studies show that patients with typical symptoms may have variable pathologic findings; conversely, typical pathologic findings can be expressed by dissimilar signs.
Findings of asymmetric onset, no evidence for other causes of parkinsonism, and no atypical features of Parkinsons Disease increase the specificity of the clinical diagnosis.