About three-quarters of patients suspected to have early Parkinson’s disease (PD) eventually prove to have other conditions, a study shows.
“This inaccuracy was present despite that all cases were examined by a small group of movement disorder specialists as opposed to many neurologists and geriatricians who examined the cases in other studies”, say lead researcher Charles Adler (Mayo Clinic, Scottsdale, Arizona, USA) and colleagues.
All of the 89 patients in the study had at least two out of three cardinal signs of PD: resting tremor, bradykinesia and cogwheel rigidity. Of these patients, 34 were classified as having possible PD, because they were untreated or had been treated for too short a time to assess their response to dopaminergic medications.
But just nine of these patients with possible PD ultimately had the disease confirmed on autopsy, giving a positive predictive value (PPV) of just 26%.
“This is a critical finding given the number of studies attempting to find biomarkers or disease-modifying treatments in very early PD cases”, the researchers write in Neurology. They say that the low proportion of patients with an accurate diagnosis “has the potential of severely compromising the likelihood of observing an adequate effect size in a trial.”
A further 97 patients were considered to have probable PD because they responded to dopaminergic medications. Among these patients, the PPV was 53% for those with a disease duration of less than 5 years at first visit, but 88% for those with a longer disease duration.
“[T]his finding supports the clinical and pathologic finding that subjects with other forms of parkinsonism may respond to dopaminergic medications early in the disease course”, notes the team.
Although more patients with probable PD and all three cardinal signs had autopsy-confirmed PD than those with just two signs, at 90% versus 76%, this difference was not statistically significant. An accurate diagnosis was significantly more likely in patients with motor fluctuations and/or dyskinesia than in those without, which the researchers say is “not surprising because fluctuations and dyskinesia help to determine responsiveness to dopaminergic medication.”
There were 16 patients with probable PD of more than 5 years’ duration who did not actually have the condition. These patients had a variety of autopsy findings, including seven with progressive supranuclear palsy and six with neurodegeneration. Three patients had no findings that accounted for their parkinsonism, and they did not have drug-induced symptoms.
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