Cerebrospinal fluid IgM index correlates with cranial MRI lesion load in patients with multiple sclerosis.

In multiple sclerosis intrathecal IgM synthesis correlates with an unfavourable disease course. Whether this reflects a pathogenic role of IgM, possibly in conjunction with complement, is a matter of debate. In a cross-sectional study we measured intrathecal synthesis of IgM and the complement component C3, and on cranial MRI lesion load and central brain atrophy in clinically active patients, 17 relapsing-remitting, 16 secondary progressive. Correlative analysis showed that in relapsing-remitting patients CSF IgM index correlated with cranial MRI T2 and T1 lesion load, and central brain atrophy; and the C3 index correlated with T2 lesion load. In secondary progressive patients CSF IgM index correlated with periventricular T2 lesion load. Our data are in favour of a pathogenic role of IgM in multiple sclerosis.