Neuromyelitis optica (NMO) is a severe demyelinating disease that affects the optic nerve and spinal cord. It is considered a variant of multiple sclerosis; however, prognosis is worse and management approach differs from that of multiple sclerosis. Differentiating NMO from more common causes of transverse myelitis (TM), particularly secondary to systemic infection, is important for prognostic and therapeutic reasons.
The diagnosis of NMO is dependent upon the identification of antibodies against aquaporin‐4. Aquaporin‐4 is the principal water channel in the central nervous system – controlling water movement between the brain, CSF and blood. It is a component of the dystroglycan protein complex located in the astrocyte foot processes at the blood brain barrier.
The original method of detection of anti‐NMO‐IgG is indirect immunofluorescence (IIF) using a composite of frozen mouse sections including cerebellum, midbrain and kidney medulla. The typical staining pattern must include staining of the renal papilla, located in the medulla of the kidney; staining around the blood vessels, pial surfaces and the Virchow‐Robin space in the cerebellum and midbrain.
We observed atypical NMO‐IgG‐like IIF staining in a patient with TM secondary to systemic melioidosis. As atypical staining could be mistaken for NMO‐IgG, we evaluated the presence of NMO‐IgG‐like IIF staining patterns in a range of patients with systemic infections. Sera from patients with serological evidence of acute infection caused by common bacterial/viral pathogens and other controls were tested using IIF. No patients fulfilled clinical or radiological criteria for NMO. IIF staining was interpreted according to the original description of NMO‐IgG.1 Several NMO‐IgG‐like IIF patterns were detected and while different staining combinations of central nervous system microvessels, pia, subpia, Virchow‐Robin space and renal papilla tubules were detected, overall patterns were atypical compared with that originally defined.1
This study demonstrates the importance of experience in interpretation of IIF and strict adherence to the original NMO‐IgG description1 to ensure the correct interpretation in patients with systemic infections that may be complicated by TM. Given clinical implications of a diagnosis of NMO, standardisation in reporting NMO‐IgG IIF to reduce the risk of reporting atypical NMO‐IgG‐like patterns as NMO‐IgG is required.
1. Lennon VA, Wingerchuk DM, Kryzer TJ, et al
. A serum autoantibody marker of neuromyelitis optica: distinction from multiple sclerosis. Lancet
2004; 364: 2106-2112.