Epidemiological studies in Thailand have reported that inflammatory demyelinating diseases (IDDs) commonly affect the optic nerve and spinal cord. We investigated the diagnostic utility of aquaporin (AQP)-4-IgG testing in 31 consecutive patients evaluated for CNS IDDs in 3 academic Thai hospital neurology clinics between February 2008 and January 2009. Patients were classified into 3 clinical diagnostic groups: Neuromyelitis optica (NMO, n=10) multiple sclerosis (MS, n=5) and unclassified IDD (n=16). All sera were tested blindly by cell binding (Euroimmun) assay (CBA). Sera were also tested by indirect immunofluorescence assay (IFA) and ELISA (RSR/Kronus). After initial screening by CBA, AQP4-IgG was detected in 6 NMO patients (60%); 3 of the 4 seronegative cases were receiving immunosuppressants. AQP4-IgG was detected in 13 unclassified IDD cases (81%), but in no MS cases. Cell binding assay and ELISA were more sensitive than IFA (p=0.0004). The 81% seropositivity rate in "unclassified" patients suggests that AQP4 autoimmunity accounts for a significant proportion of Thai CNS inflammatory demyelinating disease, especially those with optic neuritis or transverse myelitis, with or without abnormal brain MRI, in whom a specific diagnosis or clear-cut treatment approach is unclear.
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