Serum and cerebrospinal fluid proteins and the blood-brain barrier in Alzheimer's disease and multi-infarct dementia.

Serum concentrations of IgG, IgA, IgM, haptoglobin, transferrin, prealbumin and albumin quantitated nephelometrically in 22 patients with Alzheimer's disease (AD), 29 patients with multi-infarct dementia (MID) and their age-matched controls were normal. Cerebrospinal fluid (CSF) albumin and CSF/serum ratio for albumin were higher in AD and MID patients compared to controls, but no significant differences were found between AD and MID. Patients with MID had elevated CSF IgG, IgA, IgM and prealbumin levels compared to controls and to AD. An increased CSF IgG index was found in 5 MID patients but none of the AD patients. Thus, the blood-brain barrier permeability is often increased in MID as well as in AD. There is no increased intrathecal IgG synthesis in AD but it may occur in MID.