Abstract
Analysis of cerebrospinal fluid (CSF) proteins is useful in the detection of inflammatory conditions where intrathecal synthesis of immunoglobulins take place. Multiple sclerosis (MS) is an inflammatory disorder of the brain and spinal cord in which focal lymphocytic infiltration leads to damage of myelin and axons. Patients with multiple sclerosis and other demyelinating disorders, such as Subacute Sclerosing Panencephalitis, neurosyphilis, neuro-Lyme disease, cysticercosis, Systemic Lupus Erythematosus often have elevated cerebrospinal fluid (CSF) IgG concentrations due to intrathecal synthesis.Quantitatively this can be investigated with the aid of IgG index, which is the ratio of IgG concentration in the CSF-serum to albumin concentration in the CSF-serum. The IgG index reference range is 0,3 to 0,7. It is elevated in about 70% of MS patients. Qualitatively one of the best methods to detect intrathecal IgG synthesis has been to examine CSF for the presence of oligoclonal bands (OCB ...
Analysis of cerebrospinal fluid (CSF) proteins is useful in the detection of inflammatory conditions where intrathecal synthesis of immunoglobulins take place. Multiple sclerosis (MS) is an inflammatory disorder of the brain and spinal cord in which focal lymphocytic infiltration leads to damage of myelin and axons. Patients with multiple sclerosis and other demyelinating disorders, such as Subacute Sclerosing Panencephalitis, neurosyphilis, neuro-Lyme disease, cysticercosis, Systemic Lupus Erythematosus often have elevated cerebrospinal fluid (CSF) IgG concentrations due to intrathecal synthesis.Quantitatively this can be investigated with the aid of IgG index, which is the ratio of IgG concentration in the CSF-serum to albumin concentration in the CSF-serum. The IgG index reference range is 0,3 to 0,7. It is elevated in about 70% of MS patients. Qualitatively one of the best methods to detect intrathecal IgG synthesis has been to examine CSF for the presence of oligoclonal bands (OCBs) after separation of proteins by electrophoresis. IgG in normal CSF migrates as a faint diffuse zone, but in demyelinating diseases IgG migrates as discrete oligoclonal bands. Two or more IgG bands in CSF that are not detectable in corresponding serum reflect a local B-cell response accompanying Central Nervous System (CNS) inflammation. The gold standard method of demonstrating OCBs is thought to be electrophoresis of paired serum and CSF samples with isoelectric focusing (IEF) followed by immunofixation. However this method has not been adopted by many laboratories demanding a lot of time and effort.The purpose of this study was to compare the gold standard method of IEF followed by immunofixation with a commercially available technique which is semi-automated, which uses high-resolution agarose gel electrophoresis (HRAGE) directly followed by immunofixation with a peroxidase-labeled anti-IgG antiserum to detect OCBs. Additionally IgG index was calculated and compared to the results of the two quantitative methods. Paired serum and CSF samples collected from 225 patients admitted to the Department of Neurology, Athens General Hospital "G. Gennimatas" during a period of thirty six months, with the clinical suspicion of multiple sclerosis were studied for the presence of oligoclonal bands.Isoelectric focusing with IgG immunofixation was performed according to Keir and al. High-resolution agarose gel electrophoresis (HRAGE) followed by immunofixation was performed at the HYDRASYS System apparatus (SEBIA) according to the instructions of the manufacturer. The IgG index was calculated according to the type (IgGCSF/IgGserum) / (AlbumineCSF/Albumineserum). Albumine and IgG were measured using nephelometry. Values higher than 0,7 were considered positive.The agreement between the two methods (HRAGE and IEF) was 98.7% and kappa index was 0.97 (p<0.001) indicating excellent agreement between the two methods. Considering IEF as the gold standard method, among the 91 samples found to be positive with that method, 88 were also identified to be positive with HRAGE. The agreement between HRAGE and IgG index was 84.0% and kappa index was 0.65 (p<0.001) indicating good agreement between IgG index calculating and HRAGE. From the 72 samples that were classified as positive depending on the IgG index, 62 were positive with the HRAGE method. Among the patients with normal IgG index values, 28 had OBs in their CSF. On the other hand, 9 patients with elevated IgG index values, where negative for OBs.One can conclude that when CSF testing for the detection of OBs is considered necessary the semi-automated commercially available technique, which uses high-resolution agarose gel electrophoresis (HRAGE) directly followed by immunofixation with a peroxidase-labeled anti-IgG antiserum can sufficiently replace the more laborious and time consuming gold standard technique of IEF. The lower count of bands derived with the HRAGE technique, though, could affect the results in challenging situations. The quantitative IgG index cannot replace the qualitative procedures, but can become an informative, useful tool in several courses.
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