• Parkinson’s disease
• measurement
• motor complications

The development of dyskinesias and motor fluctuations is a major concern related to dopaminergic treatment for Parkinson’s disease. These motor complications are common,¹ and can be a significant source of disability.^2,3 Numerous clinical trials have been conducted to compare treatments for their ability to delay, prevent, or reduce the severity of motor complications. Measuring motor complications is challenging because of the number of potentially important aspects, including frequency, intensity, predictability, phenomenology, as well as the need to rely on a subject’s understanding and awareness of these phenomena because they are transient, often under-recognised by the affected patient, and often cannot be observed directly by study personnel.

As shown in table 1⇓, the proportion of subjects experiencing motor complications with initial levodopa therapy recorded by several recent randomised, controlled trials of initial treatment of Parkinson’s disease varies considerably.^4–,¹³ For example, the proportion of subjects recorded as having dyskinesias at five years of follow up varies across studies from 5% to 41%. All of these trials recruited patients from similar populations who received levodopa in doses adjusted according to their individual needs. We examine the methods of measuring motor complications used in these trials as a source of variability in the results, and consider the implications of this variability for the results of clinical trials in this area and for the interpretation of the literature.

Table 2⇓ summarises the methods used to record motor complications in clinical trials of early treatment for Parkinson’s disease in which the occurrence of motor complications was a primary outcome.^4–,¹⁴ Potential sources of variability in the results …