Lower brain diffusivity in postpartum period compared to late pregnancy: results from a prospective imaging study of...

A positive correlation has been observed between multiple sclerosis (MS) disease activity status and the apparent diffusion coefficient (ADC) of the brain. Moreover, the relapse frequency of MS has been reported to decrease during pregnancy and increase postpartum. The aim of this study was to evaluate whether ADC histograms correlate with MS activity during pregnancy and postpartum, with a leading hypothesis that the ADC would increase postpartum compared to pregnancy.

Magnetic resonance imaging, as well as diffusion-weighted imaging, was performed in 19 patients with relapsing-remitting MS once during the third trimester and once 4-12 weeks postpartum. Brain tissue was extracted from nonbrain tissue with an automated computer program, and whole-brain histograms were generated. New or growing T2 lesions in postpartum images were counted on T2-weighted images.

In conventional brain magnetic resonance imaging, a significant increase in T2-lesion load was seen in postpartum images; 58% of patients showed signs of disease activity on their postpartum scan. Despite of this, and contrary to the original hypothesis, whole-brain ADC values were significantly lower in the postpartum period compared to the time of pregnancy.

This is the first study to address the ADC of the brain during pregnancy and postpartum period. We hypothesize that the higher ADC values observed during pregnancy in this study reflect the physiological status of the cerebral vasculature during pregnancy (generalized vasodilatation of downstream resistance arterioles and an increase of endothelial permeability), which overwhelm the alterations in ADC values normally seen related to MS activity.