Lessons from traumatic head injury for assessing functional status after brain tumour.

Assessment of global functional status plays a central role in describing outcome after traumatic head injury, but has played a relatively minor role as an endpoint in brain tumour studies. Advantages of functional status as an outcome include simplicity, objectivity, and interpretability, and it is particularly useful in conditions where cognitive impairment is common. Work in the field of traumatic brain injury, specifically on the Glasgow Outcome Scale (GOS), provides lessons in how the validity and reliability of global outcome assessment can be improved. Functional status is conceptually and empirically distinct from cognition and health-related quality of life, and neither of these can adequately substitute for it as an outcome. The strongest candidate for a global outcome measure in brain tumour work is the Karnofsky Performance Status (KPS). Many of the lessons from the GOS could be applied to improvement of KPS assessment. However, the KPS has additional limitations, particularly that it is not brain injury specific. Global functional status is potentially a useful outcome for brain tumour studies, but there is a gap in the tools currently available.