Depression and apathy can be significant problems in progressive supranuclear palsy (PSP). Using PRISMA guidelines, this systematic review examined prevalence estimates for depression and apathy in PSP, and, how different methods of definition may influence results. 29 studies meeting inclusion/exclusion criteria were identified: 12 on depression, 9 on apathy, and 8 on both. Studies were stratified according to whether a diagnostic criteria, rating scale or screening question methodology was employed. The weighted mean prevalence was 59.7% for depression (sample size = 473) and 58.3% for apathy (sample size = 858). Results for depression using diagnostic criteria or rating scales were similar whereas screening questions were associated with considerable inconsistency. Depression prevalence appeared to be influenced by apathy but not somatic symptoms. Most apathy studies relied only on a screening question method. Depression and apathy are common in PSP but there is a need for consensus on how they are defined (both tools and cut-off scores). In particular, more studies probing apathy in greater detail than a simple screening question are required.
Keywords: apathy; depression; progressive supranuclear palsy.