Diagnostic value of aquaporin-4-IgG live cell based assay in neuromyelitis optica spectrum disorders

Abstract

Objective Determine the utility of aquaporin 4 IgG (AQP4-IgG) testing (live cell-based assay) for Neuromyelitis Optica Spectrum Disorders (NMOSD). Methods We included Mayo Clinic patients (1/1/2018-12/31/2019) tested for serum AQP4-IgG by live cell-based flow-cytometric assay. Medical records were reviewed to assess if patients fulfilled 2015 NMOSD criteria. Results Of 1371 patients tested, 41 were positive (3%) and all fulfilled NMOSD criteria with AQP4-IgG (specificity = 100%). Only 10/1330 testing negative met NMOSD criteria without AQP4-IgG (sensitivity = 80%) and seven of these 10 were MOG-IgG positive. Conclusions AQP4-IgG by live cell-based assay was highly specific and without false positives in a high throughput setting.

Myelin Oligodendrocyte Glycoprotein Antibody-Associated Disease (MOGAD): A Review of Clinical and MRI Features, Diagnosis, and Management

“…In 2007, a seminal study by O'Connor et al showed that laboratory assays expressing MOG in its tridimensional conformational form (rather than linear epitopes targeted on denaturated proteins as with other assays) identified a sub-set of conformation-sensitive MOG-IgG in patients with acute disseminated encephalomyelitis (ADEM) or optic neuritis, but not in patients with MS (2). Subsequent studies using cell-based assays expressing human full length MOG on mammalian cells confirmed the detection of MOG-IgG in patients with non-MS demyelinating CNS disorders (16,17), including 30-70% of patients with seronegative NMOSD (18)(19)(20)(21). The spectrum of clinical-MRI manifestations associated with MOG-IgG is now recognized to extend beyond the NMOSD phenotype and the disease is referred to as MOGAD (22)(23)(24).…”

“…Two major limitations for a robust assessment of MOG-IgG seroprevalence in a population include: (1) MOG-IgG titer may drop to undetectable after disease attacks (i.e., MOGAD patients tested during remission may result negative and erroneously be excluded from a study); and (2) screening of large populations for epidemiology purposes increases the risk of false positive results (see also "Atypical clinical-MRI phenotypes and risk of false positivity" below). Similar problems are not encountered with AQP4-IgG+NMOSD for which antibody positivity persists over time and the risk of false positive results using cell-based assay technique is negligible (19).…”

Educational Case: Neuromyelitis optica

“… 15 A positive cell-based assay for AQP4-IgG has a specificity of 90.6%–100% for the diagnosis of NMOSD. 16 A cell-based assay has a slightly higher sensitivity (76%) and specificity (99%) when compared to a tissue-based assay (59.0%; 97.0%) and an enzyme-linked immunosorbent assay (65%; 97%). 15 AQP4 channels are present in the foot processes of astrocytes that are direct contact with the pia mater, capillaries, neurons and in ependymal cells.…”

Serum and Cerebrospinal Fluid Biomarkers in Neuromyelitis Optica Spectrum Disorder and Myelin Oligodendrocyte Glycoprotein Associated Disease

“…Indeed, some patients that tested positive on ELISA but negative with CBA had alternative diagnoses identified suggesting a potential for false positivity ( 21 ). Even though early reports preferred immunofluorescence over FACS ( 19 ), live cell-based assays (either live or fixed) either detected by FACS or by visual immunofluorescence have very high specificity ( 22 ). Immunohistochemistry may be useful to detect the typical AQP4-IgG staining patterns on rodent tissue composite, but then AQP4-IgG presence should be confirmed using CBAs ( 23 ).…”