Functional cognitive disorder: dementia’s blind spot - a reply

Extract
We welcome the comments from Kapur et al.1 and the opportunity to clarify the meaning of internal inconsistency. This is not equivalent to identifying fluctuations over time, since that could occur for many reasons. Rather, the defining feature of internal inconsistency is contrasting function and dysfunction, ideally demonstrable at the same time, analogous to Hoover’s sign in functional motor weakness. Function should be tested using different approaches to see if discrepant results are obtained. This would indicate a lack of factors other than attention and focus that can explain it. When one encounters either temporal variability, or subjective cognitive concern but no objective deficit, this is not in itself specific enough to represent internal inconsistency. Instead, it should be a flag to explore and contrast the specific tasks that the person is, and is not, able to perform. This must be considered in the context of the patient’s whole presentation, and relevant differentials considered.