Objective To determine the effect of intravenous immunoglobulin (IVIG) on brain atrophy and cognitive function in mild cognitive impairment (MCI) due to Alzheimer's disease (AD).

Methods 50 participant 50–84 years of age with amnestic MCI were administered 0.4 g/kg 10% IVIG or 0.9% saline every 2 weeks for a total of 5 infusions (2 g/kg total dose) in a randomised double-blinded design. MRI brain was completed at baseline, 12  and 24 months. Cognitive testing was completed at baseline and every 4 months. Participants were stratified into early and late (LMCI) MCI stages. Average annualised per cent change in ventricular volume was computed as a measure of brain atrophy.

Results There was significantly less brain atrophy (p=0.037, adjusted for MCI status) in the IVIG group (5.87%) when compared with placebo (8.14%) at 12 months; at 24 months, the reduction in brain atrophy no longer reached statistical significance. The LMCI participants who received IVIG performed better on Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog; p=0.011) and Mini-Mental State Examination (MMSE; p=0.004) at 1 year; these differences were not present after 2 years. There was no difference in conversion to AD dementia between the treatment and control groups after 2 years; however, at 1 year, there were fewer conversions from LMCI to AD dementia in the IVIG group (33.3%) when compared with control group (58.3%).

Conclusions This exploratory study provides limited evidence that a short course of IVIG administered in the MCI stage of AD reduces brain atrophy, prevents cognitive decline in LMCI and delays conversion to AD dementia for at least 1 year; however, this effect of IVIG appears to wane by 2 years.

Trial registration number ClinicalTrials.gov, NCT01300728.