Objective To investigate the effect on survival of treatment with memantine in patients with dementia with Lewy bodies (DLB) and Parkinson's disease with dementia (PDD).

Methods 75 patients with DLB and PDD were included in a prospective double-blinded randomised placebo-controlled trial (RCT) of memantine, of whom long-term follow-up was available for 42. Treatment response was recorded 24 weeks from baseline and measured by Clinical Global Impression of Change (CGIC). The participants were grouped as responders (CGIC 1–3) or non-responders (CGIC 4–7). The 24-week RCT was followed by open-label treatment and survival was recorded at 36 months.

Results After 36-month follow-up, patients in the memantine group had a longer length of survival compared with patients in the placebo group (log rank x²=4.02, p=0.045). Within the active treatment group, survival analysis 36 months from baseline showed that the memantine responders, based on CGIC, had higher rates of survival compared with the non-responders (log rank x²=6.595, p=0.010). Similar results were not seen in the placebo group.

Conclusions Early treatment with memantine and a positive clinical response to memantine predicted longer survival in patients with DLB and PDD. This suggests a possible disease-modifying effect and also has implications for health economic analysis. However, owing to the small study sample, our results should merely be considered as generating a hypothesis which needs to be evaluated in larger studies.

Trial registration number ISRCTN89624516.