From the Guidelines
Cerebrospinal fluid (CSF) analysis is crucial for diagnosing neuromyelitis optica (NMO), and it typically shows pleocytosis with a predominance of neutrophils, with a white blood cell count often exceeding 50 cells/μL, and protein levels usually elevated (>100 mg/dL). In NMO, CSF findings can mimic CNS infection with neutrophil pleocytosis, impaired blood-CSF barrier function, and a lack of CSF-restricted oligoclonal bands 1. The most specific laboratory test for NMO is serum aquaporin-4 immunoglobulin G (AQP4-IgG) antibody testing, which has high specificity (>99%) but variable sensitivity (60-90%) 1. If AQP4-IgG is negative but NMO is still suspected, testing for myelin oligodendrocyte glycoprotein (MOG) antibodies should be considered, as some patients with NMO-like presentations are MOG-antibody positive 1. Some key CSF findings that may indicate NMO include:
- Neutrophilic CSF pleocytosis or CSF WCC > 50/μl 1
- No CSF-restricted OCB as detected by IEF at first or any follow-up examination 1 CSF analysis should be performed during acute attacks before treatment initiation for optimal diagnostic yield, as immunosuppressive therapy can alter the findings 1. It's also important to consider other diagnostic criteria, such as MRI findings, clinical symptoms, and serology results, to confirm the diagnosis of NMO 1.
From the Research
CSF Labs for NMO
- The cerebrospinal fluid (CSF) profile of AQP4-Ab positive patients with NMO or its formes frustes has been analyzed in a study published in the Journal of the neurological sciences 2.
- The study found that CSF-restricted oligoclonal IgG bands, a hallmark of MS, were absent in most patients, and if present, intrathecal IgG synthesis was low, transient, and restricted to acute relapses.
- CSF pleocytosis was present in around 50% of samples, and albumin CSF/serum ratios, total protein, and CSF L-lactate levels correlated significantly with disease activity and the length of spinal cord lesions in patients with acute myelitis.
Key Findings
- AQP4-Ab positive NMOSD is characterized by CSF features that are distinct from those in MS 2.
- The presence of CSF oligoclonal bands (OCBs) in NMOSD patients is associated with higher CSF cell counts and a higher likelihood of concomitant connective tissue disease and other autoimmune antibodies 3.
- The diagnostic criteria for NMO have evolved over time, and the identification of AQP4-IgG antibodies has played a significant role in the diagnosis and management of the disease 4, 5, 6.
Laboratory Characteristics
- The study published in Frontiers in immunology found that OCBs+ patients had higher CSF cell counts, higher IgG index, and more relapses within 36 months compared to OCBs- patients 3.
- The presence of OCBs in NMOSD patients may predict more frequent relapses, but not a more serious illness 3.
- The CSF findings in AQP4-Ab positive NMOSD patients differ significantly from those in MS, and these differences are important for the differential diagnosis of MS and NMOSD 2.