Multiple sclerosis is a chronic demyelinating disease that has a reputation for recurrent illness of unpredictable length and severity. A multifocal demyelinating process in cerebral hemisphere white matter results in various combinations of weakness, ataxia, vision difficulties, and parasthesias, frequently ending in paralysis. Thus, the clinical symptoms, especially early in the disease, can be mimicked by a considerable number of other conditions.

Cerebrospinal fluid laboratory findings. Routine CSF test findings are nonspecific, and when abnormality is present, the standard CNS test results are similar to those of aseptic meningitis. The CSF total protein is increased in about 25% of cases (literature range, 13%-63%). The cell count is increased in about 30% of cases (literature range, 25%-45%), with the increase usually being mononuclear in type and relatively small in degree.

The CSF gamma-globulin (IgG) level is increased in 60%-80% of cases (literature range, 20%-88%). Technical methods such as radial immunodiffusion produce more accurate results than electrophoresis. Problems have been recognized in interpretation of CSF gamma-globulin values because elevated serum gamma-globulin levels can diffuse into the CSF and affect values there. Many investigators analyze a specimen of serum as well as of CSF to see if the serum gamma-globulin level is increased. Several ratios have been devised to correct for or point toward peripheral blood protein contamination. The most widely used is the CSF IgG/albumin ratio. Albumin is synthesized in the liver but not in the CNS and therefore can be used to some degree as a marker for serum protein diffusion into the CSF or introduction into the CSF through traumatic lumbar puncture or intracerebral hemorrhage. The IgG/albumin ratio is based on the theory that if serum leaks or is deposited into spinal fluid, albumin and IgG will be present in roughly the same proportion that they have in serum; whereas a disproportionate elevation of IgG relative to albumin suggests actual production of the IgG within the CNS. The normal CSF IgG/albumin ratio is less than 25% (literature range, 22%-28%). About 70% of MS patients have elevated IgG/albumin ratios (literature range, 59%-90%). The IgG/albumin ratio is a little more specific for MS than increase of IgG by itself. However, many conditions produce increased IgG within the CNS, such as chronic CNS infections, brain tissue destruction, CNS vasculitis, systemic lupus erythematosus and primary Sjцgren’s syndrome involving the CNS, and various demyelinating diseases.

Another way to estimate CNS production of IgG is the IgG index, which is (CSF IgG level/CSF albumin level) ч (serum IgG level/serum albumin level). This index is reported to be abnormal in about 85% (range, 60%-94%) of definite MS patients. A third method for estimating CNS IgG production is the IgG synthesis rate formula of Tourtellote. Sensitivity of this method is about 85% (range, 70%-96%). Consensus seems to be that the IgG index is slightly more sensitive and reproducible than the IgG synthesis rate. Both can be influenced by altered blood-brain barrier permeability or presence of blood in the CSF as well as the various conditions other than MS that induce CNS production of IgG antibody.

Another useful test is based on the observation that patients with MS demonstrate several narrow bands (“oligoclonal bands”) in the gamma area when their spinal fluid is subjected to certain types of electrophoresis (polyacrylamide gel, high-resolution agarose, or immunofixation; ordinary cellulose acetate electrophoresis will not demonstrate the oligoclonal bands). Oligoclonal banding is present in 85%-90% of MS patients (literature range, 65%-100%. Some of this variation is due to different methods used). Similar narrow bands may be found in subacute sclerosing panencephalitis, destructive CNS lesions, CNS vasculitis, lupus or primary Sjцgren’s syndrome involving the CNS, diabetes mellitus, and the Guillain-Barrй syndrome. A similar but not identical phenomenon has been reported in some patients with aseptic meningitis.

Antibodies have been produced against myelin components, and a radioassay for myelin basic protein (MBP) is available in some reference laboratories. The MBP level is reported to be increased in 70%-80% of patients with active MS (literature range, 62%-93%), depending to some extent on the status of active demyelination. Incidence is less if the disease is not active or if steroid therapy is being given. The various demyelinating conditions other than MS also produce abnormal MBP assay results. The MBP level may also be increased in destructive CNS lesions such as a CVA, in some patients with the Guillain-Barrй syndrome, and in some patients with CNS lupus erythematosus.

Summary. Of the various laboratory tests for MS, the two most widely used are the spinal fluid IgG index and presence of oligoclonal bands. Of these, the best single test is probably oligoclonal banding. CT and MRI can often demonstrate focal demyelinized areas in the CNS, with CT reported to show abnormality in 40%-60% of patients with definite MS and MRI positive findings in about 90% (range, 80%-100%). Neither CT nor MRI is currently able to differentiate MS with certainty from other CNS demyelinizing diseases.