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Abstract
Background: Detection of serum antibodies to myelin-associated glycoprotein (MAG) by Western blot (WB) is a valuable assay to diagnose a distinct type of demyelinating polyneuropathy with immunoglobulin M (IgM) monoclonal gammopathy. In this study, the diagnostic accuracy of a new and more practical ELISA to detect these antibodies was validated.
Methods: Routine WBs from 2 independent laboratories and ELISA were used to detect anti-MAG IgM in serum from 207 patients with neuropathy and controls. The sensitivity and specificity of these assays were compared and related to the patient clinical and electrophysiologic characteristics.
Results: In ELISA, anti-MAG antibodies were found in serum from 49 (72%) of 68 patients with demyelinating polyneuropathy and IgM monoclonal gammopathy. However, in this subgroup of patients, only 30 (44%) and 37 (54%) were positive in the 2 WBs. All of the patients positive in the 2 WBs were also positive in ELISA. A high correlation was found for IgM activity in ELISA to MAG and sulfate-3-glucuronyl paragloboside (SGPG) (Spearman ρ = 0.72, p < 0.0001), supporting the notion that the shared sulfated glucuronic acid moiety of MAG and SGPG is preserved. Most patients positive in anti-MAG ELISA had a slowly progressive sensory–motor demyelinating polyneuropathy, even if the WB was negative. In control groups, however, 4 WB-negative patients with a nondemyelinating monoclonal gammopathy–related polyneuropathy were positive in anti-MAG ELISA. The remaining samples were negative in ELISA.
Conclusion: ELISA is more sensitive than Western blot to diagnose anti–myelin-associated glycoprotein related polyneuropathy, although a positive serology may be found in other forms of polyneuropathy as well.
Glossary
- BTU=
- Bühlmann titer unit;
- IgM=
- immunoglobulin M;
- MAG=
- myelin-associated glycoprotein;
- ROC=
- receiver operating characteristic;
- SDS-PAGE=
- sodium dodecyl sulfate polyacrylamide gel electrophoresis;
- SGPG=
- sulfate-3-glucuronyl paragloboside;
- UMCU=
- University Medical Center of Utrecht;
- WB=
- Western blot.
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