AQP4IgGpositive

AQP4IgGpositive refers to the presence of immunoglobulin G antibodies against aquaporin-4 (AQP4) in a person’s serum or plasma. AQP4 is a water channel expressed on astrocytes in the central nervous system. Detection of AQP4-IgG is used as a biomarker for neuromyelitis optica spectrum disorder (NMOSD) and related inflammatory neurologic conditions. The cell-based assay is the preferred method for testing, with high specificity for NMOSD; positivity supports a diagnosis of NMOSD in the appropriate clinical context. False negatives can occur, and some individuals with AQP4-IgG–negative serology may still have NMOSD, particularly if clinically suspected.

AQP4-IgG positivity is strongly associated with inflammatory lesions of the optic nerves, spinal cord (often longitudinally extensive transverse myelitis), area postrema region (causing intractable nausea or hiccups), diencephalon, or brainstem, consistent with NMOSD. Pathophysiology involves antibody-mediated injury to astrocytes, complement activation, and secondary demyelination.

Diagnosis relies on compatible clinical features together with AQP4-IgG serostatus, supported by MRI findings. Seropositivity is typically considered in conjunction with core clinical characteristics, and MOG-IgG testing may be performed to distinguish from MOG antibody-associated disease.

Management focuses on preventing relapses and treating acute attacks, using immunosuppressive therapies such as corticosteroids for acute events and long-term agents (e.g., rituximab, azathioprine, mycophenolate; newer targeted therapies include eculizumab, inebilizumab, and satralizumab). The prognosis varies, but relapse prevention improves long-term outcomes.