Dutch researchers said they have found a way to distinguish atypical Parkinson's disease from the more common standard form: asking patients if they can still ride a bicycle.
When the question was put to 111 consecutive patients with Parkinson's disease, nearly all those who said it had become impossible were subsequently determined to have the atypical form, according to Bastiaan Bloem and colleagues at Nijmegen Medical Center in the Netherlands.
"Simply asking about cycling abilities could be added to the list of red flags that can assist clinicians in their early differential diagnosis of parkinsonism," they reported in the Jan. 8 issue of The Lancet.
They noted that it is often clinically difficult to determine whether patients with clear symptoms of Parkinson's disease have an atypical form that, as the disease progresses, includes symptoms not normally seen in the typical presentation.
Whereas "regular" Parkinson's disease is caused by loss of dopaminergic neurons in the substantia nigra, patients with atypical disease also show degeneration in the striatum. The underlying cause of atypical versus typical disease may also differ.
The difference is important both for advising patients on what to expect in the future and for recruitment in clinical trials of Parkinson's disease therapies, noted Bloem and colleagues, who conducted structured interviews with 156 Parkinson's patients who had not yet received a definitive diagnosis.
At study entry, patients were asked if they had ridden a bicycle before developing symptoms and, if so, whether, when, and why they no longer could. The 45 patients who said they were not bike riders were excluded from the analysis.
The final determination of whether patients had atypical or typical Parkinson's disease was made three years after the initial interview, on the basis of response to treatment, neurological exams, and MRI studies. Typical disease was diagnosed in 45 patients and atypical syndromes in 66.
During the baseline interview, 36 patients said they were no longer able to ride a bicycle. Of those, only two were later diagnosed with typical Parkinson's disease.
Bloem and colleagues indicated the loss of cycling ability was seen for all subtypes of atypical disease.
"Regression analysis revealed no significant effect of age, parkinsonism, or ataxia on the ability to cycle, suggesting that this was an independent marker of atypical parkinsonism," they added.
The researchers also suggested that the "more extensive extranigral pathology" seen in atypical forms may be responsible for the inability to manage a bicycle.
"Cycling requires a highly coordinated interplay between balance, coordination, and rhythmic pedalling of the legs," they pointed out. As a result, small defects in any of these components could disrupt cycling ability, they argued.
However, because the study was conducted in the Netherlands -- where, as the baseline data showed, many adults ride bicycles regularly -- the findings may not be generalizable to U.S. patients.
Neurologists in the U.S. contacted by MedPage Today and ABC News agreed that the findings were intriguing and made sense from their own clinical experiences.
"Atypical parkinsonism patients do tend to have more balance issues, and a complicated motor task requiring intact balance may provide a reasonable prognostic clue," said Dr. Mark Stacy of Duke University in an e-mail.