CEREBROSPINAL-FLUID TAU-PROTEIN AS A BIOCHEMICAL MARKER FOR ALZHEIMERS-DISEASE - A COMMUNITY-BASED FOLLOW-UP-STUDY

Objectives-Biochemical markers for Alzheimer's disease would be of gre at value, especially to help in diagnosis early in the course of the d isease. A pronounced increase in CSF tau protein (CSF-tau) is found in most patients with Alzheimer's disease. However, the specificity has to be further studied, as an increase in CSF-tau has also been found i n other dementias, especially in vascular dementia. As most previous C SF studies have been based on selected inpatients, it was considered o f special interest to examine the diagnostic potential of CSF-tau in a community population based sample of consecutive patients with dement ia. Such patient material has been examined at the Pitea River Valley Hospital in Northern Sweden since 1986, and includes all those with me mory disturbances in the community. The aim was also to study if an in crease in CSF-tau is found early in the disease process, and whether C SF-tau changes during the progression of disease. Methods-Participants : Community population based sample of 75 demented patients (43 with A lzheimer's disease, 21 with vascular dementia, and 11 with mixed Alzhe imer's disease/vascular dementia), 18 healthy subjects, and 18 neurolo gical controls. A follow up investigation (including analysis of a new CSF sample) was performed in all patients after about one year. Main outcome measures-Concentrations of total (both normal tau and PHF-tau) tau in CSF, clinical measures (duration and severity of dementia), an d apoE polymorphism. Results-CSF-tau was markedly increased in Alzheim er's disease, 41/43 (95%) patients had values above the cut off level (mean+2 SD) in controls (306 pg/ml). High CSF-tau concentrations were also found in most patients with vascular dementia, preferentially in patients with vascular dementia without progressive leukoaraiosis on C T, whereas patients with vascular dementia with progressive leukoaraio sis had normal CSF-tau. Concentrations of CSF-tau were stable at one y ear follow up in both patients with Alzheimer's disease and patients w ith vascular dementia, and there was no correlation between CSF-tau an d either duration or severity of dementia. Conclusions-The findings co nfirm the high sensitivity of CSF-tau for the diagnosis of Alzheimer's disease, but high CSF-tau was also found in vascular dementia, result ing in a lower specificity. However, high CSF-tau is preferentially fo und in patients with vascular dementia without progressive leukoaraios is, which may constitute a group with concomitant Alzheimer's disease pathology. High CSF-tau may be present during the whole course of the disease in Alzheimer's disease. Possibly, therefore, the same high CSF -tau concentrations may be present before the onset of clinical dement ia. Follow up studies on such patients will tell whether analysis of C SF-tau is useful as a biochemical marker for early Alzheimer's disease .