Co-occurrence of different pathologies in dementia: implications for dementia diagnosis

The standard for differentiating between dementia subtypes is currently based on neuropathological changes and follows traditional nosological classifications. However, the high incidence of comorbid neuropathologies complicates the differentiation between dementia diagnoses in the clinic. The aim of this study was to investigate the grades of agreement between clinical and neuropathological diagnoses in neurodegenerative disorders, to compare them with rates found in previous studies, and to propose implications for dementia diagnostics. Patients, who donated their brains to the Brain Bank of Navarre (Pamplona, Spain), had been diagnosed with a neurodegenerative disorder during life (clinical diagnosis) and postmortem (neuropathological diagnosis). We studied a sample of patients with a short average time interval between the last clinical assessment and death (4.6 months). Overall, there was a mean grade of agreement of 44.0% between the clinical diagnosis and the pure neuropathological diagnosis (i.e., without co-morbid neuropathological disorders). This grade of agreement differed between dementia subtypes: e.g., 85% for prion disease, 49% for Alzheimer's disease, and 0% for Lewy body dementia. Our data confirm that co-occurrence of multiple neuropathological disorders is very common in individuals with dementia, and that the underlying neuropathology often differs from the neuropathology implied by the clinical diagnosis. These findings support a multidimensional approach to diagnosing dementia, in which dementia syndromes are not categorized into diagnostic subtypes, but are seen as syndromes characterized by a combination of various neuropathological dimensions.