Clinimetric issues of screening for responsiveness to intrathecal baclofen in dystonia

Summary.

Objectives. In this study we address clinimetric issues that pertain to the screening of responsiveness to intrathecal baclofen (ITB) in dystonia. Methods. Eight patients with severe dystonia, who did not respond to oral medication, were evaluated in a double-blind placebo controlled ascending dose screening procedure, which included a randomised sequence of injections of 25, 50 and 75 μg baclofen and placebo. Self-assessments of dystonia severity on a visual analogue scale (VAS) and the Dyskinesia Rating Scale (DRS) were carried out at baseline 1, 4 and 8 hours after a bolus injection. Results. Compared to the VAS, the DRS lacked responsiveness in all patients. Baseline scores of the VAS scores varied considerably between and within patients and underscore the need to express response scores in relation to the baseline. After placebo administration some patients showed a persistent improvement of about 30% across the day, while at some assessments improvements of >50% were noted. Based on the aforementioned findings, a responsiveness coefficient was used which relates the baclofen effect size to the non-specific score changes that may occur as a placebo effect or as random fluctuations in dystonia. Four patients with a responsiveness coefficient >2 received pump implantation and did well on continuous infusion of ITB. Several side effects occurred during the screening procedure, but none interfered with the execution of the screening procedure. Conclusions. This study demonstrates important clinimetric issues that need to be taken into account when screening for responsiveness to ITB.