Cerebrospinal fluid IgM, IgA, and IgG indexes in systemic lupus erythematosus. Their use as estimates of central nervous system disease activity.

Paired serum and cerebrospinal fluid (CSF) specimens from 13 patients with systemic lupus erythematosus (SLE) and central nervous system involvement (CNS-SLE) were studied for CSF IgM, IgA, and IgG indexes (indicators of intrathecal immunoglobulin synthesis) and CSF-serum albumin quotient (Q albumin) (an indicator of blood-brain-barrier function). We also studied 20 patients with noninflammatory neurologic diseases and seven patients with SLE without CNS involvement for comparison. In addition to an increase in the CSF IgG index, IgM and IgA indexes also were elevated in patients with CNS-SLE. All three indexes decreased significantly when CNS manifestations subsided by successful treatment. The Q albumin was normal in most patients. The elevation of CSF immunoglobulin indexes may be a result of polyclonal B-lymphocyte activation within the CNS, rather than the leak of immunoglobulins from the systemic circulation into the CNS. Since these indexes reflect CNS disease activity in SLE, they may be a successful tool for the management of SLE.