The rate of diagnostic accuracy is lower in early disease and higher in later disease and is improved by medication response and other factors.
The rate of accuracy for a clinical diagnosis of Parkinson disease (PD) is only 26% in untreated patients and patients with PD that is not clearly responsive to medication, according to the findings of a new study. The rate increases to 53% in patients with early PD (less than 5 years of disease duration) responsive to medication and to more than 85% in patients with medication-responsive PD of longer duration.
Adler and colleagues from the Parkinson’s Disease and Movement Disorders Center, Department of Neurology, and Department of Biostatistics, Mayo Clinic, Scottsdale, Arizona, and other centers conducted their study with data from the Arizona Study of Aging and Neurodegenerative Disorders to determine the predictive value of a clinical PD diagnosis. They used 2 clinical diagnostic confidence levels, PossPD (never treated or not clearly responsive to medications) and ProbPD (responsive to medications). Neuropathologic findings were used as the gold standard in determining the accuracy of diagnosis.
In 9 of 34 PossPD cases and 80 of 97 ProbPD cases, PD was confirmed based on the first visit. PD was confirmed in 8 of 15 ProbPD cases with less than 5 years of disease duration and in 72 of 82 cases with 5 years or more of disease duration. According to final diagnosis at time of death, 91 of 107 ProbPD cases had confirmed PD. Diagnostic accuracy was improved by medication response, motor fluctuations, dyskinesias, and hyposmia.
The study provides Class II evidence that a clinical diagnosis of PD identifies patients who will have pathologically confirmed PD, with sensitivity and specificity of 88% and 68%, respectively, the researchers stated. They noted that caution is needed when interpreting clinical studies of PD, especially studies of early disease that do not have autopsy confirmation, and that the need for a tissue or other diagnostic biomarker is reinforced.
The study was published online before print on June 27, 2014, in the journal Neurology.
In an accompanying editorial, Rajput and Rajput from the Movement Disorders Program Saskatchewan, University of Saskatchewan/Saskatoon Health Region, Canada, maintained that when all the PD cases reported by Adler et al. are compared with the PD cases in previous reports, the diagnostic accuracy is remarkably similar, indicating that the clinical diagnostic capabilities for PD have not advanced substantially over the last few decades. They suggested that the challenge is to find methods or tools to accurately predict the underlying pathology in the earlier cases.