Motor progression in Parkinson’s disease is non-linear and occurs in three distinct phases, all of which are affected by baseline variables such as gender, age at diagnosis, disease subtype, cognitive status and motor score, study findings indicate.
During a follow-up period of up to 9 years (minimum 3 years), the researchers found that motor score progression, defined as the change in Unified Parkinson’s Disease Rating Scale motor scores from baseline, ranged from 0.62% to 3.67% per year in their cohort of 576 patients (mean age 63.7 years, 57% men) with Parkinson’s disease.
However, the researchers note that the confidence intervals for motor progression were wide, indicating variability among the patients, who all underwent their baseline assessment within 2 years of diagnosis.
As well as individual variation, Louis Tan (National Neuroscience Institute, Singapore) and colleagues observed three distinct phases of motor progression. Phase I showed a significant 3.33-point (3.08%) improvement from baseline during the first 2 years.
During phase II, patients’ motor scores rose to their baseline level 2.0 to 2.5 years after diagnosis and remained stable for up to 7 years postdiagnosis.
And through phase III there was significant motor progression from year 7 until the end of follow-up, with an average progression rate of 1.96% per year during this time.
Tan and team also evaluated the effect of several baseline variables on motor progression.
They report in the European Journal of Neurology that men and women both showed improvements in the first year, but male scores returned to baseline levels more quickly and remained significantly higher than female scores up to 6.5 years postdiagnosis. From this point onwards, men and women showed a similar trend, indicating that women have a slower rate of progression in the early stages but a faster rate of progression during the later phase of the disease.
The team also found that older age at diagnosis (>50 years) was a predictor of greater progression, particularly after 4 years postdiagnosis, as was cognitive impairment. Indeed, patients with no cognitive impairment at baseline experienced significant improvements in motor score for up to 7 years, whereas the scores of those who were cognitively impaired had returned to baseline levels by 3.5 years.
Lower baseline motor score and akinetic-rigid subtype were also associated with greater progression of motor scores, but ethnicity, type of medication and baseline Hoehn and Yahr stage were not.
“Our results suggest that averaging the rate of change over long periods, as well as using extrapolated or projected rates, does not adequately characterize disease progression and might miss the intricacies within the different phases”, Tan and co-authors conclude.
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