Laboratory Work for Acute MS Flare
For an acute MS flare in a patient with established MS, routine laboratory testing is generally not necessary unless you need to exclude infection or other mimics triggering the symptoms.
Core Laboratory Approach
The laboratory workup during an acute MS flare differs fundamentally from initial diagnostic evaluation. Since the diagnosis is already established, testing should be targeted and purposeful:
Essential Testing (Only When Clinically Indicated)
- Complete blood count (CBC) with differential - Order this if you suspect infection as a trigger or mimic of the flare, particularly if the patient has fever or systemic symptoms
- Urinalysis and urine culture - Critical to exclude urinary tract infection, which commonly triggers pseudoexacerbations in MS patients
- Basic metabolic panel - Useful if considering corticosteroid treatment (check glucose, electrolytes, renal function) or if metabolic derangements might explain symptom worsening
When CSF Analysis May Be Warranted
CSF studies are NOT routinely needed for established MS flares 1. However, consider lumbar puncture in specific scenarios:
- Atypical presentation that raises concern for alternative diagnosis
- Suspicion of CNS infection (meningitis/encephalitis)
- Concern for neuromyelitis optica spectrum disorder (NMOSD) if longitudinally extensive transverse myelitis is present 2
- First clinical event where diagnosis remains uncertain
If CSF is obtained, the relevant studies include:
- Cell count and differential (elevated WBCs suggest infection or other inflammatory process)
- Protein and glucose
- Oligoclonal bands (for diagnostic purposes only, not monitoring) 3
- Consider infectious studies if clinically appropriate
Critical Differential Diagnosis Testing
The 2010 McDonald criteria emphasize that exclusion of alternative diagnoses is imperative 4. For acute flares with atypical features, consider:
Red Flag Scenarios Requiring Additional Testing
- Age >50 years or vascular risk factors: These patients need more stringent evaluation to avoid misdiagnosis 5
- Longitudinally extensive spinal cord lesions (≥3 segments): Check aquaporin-4 antibodies (AQP4-IgG) to exclude NMOSD 2
- Optic neuritis with atypical features: Consider AQP4-IgG and MOG antibodies
- Systemic symptoms: ANA, ESR may be considered but have poor specificity 6
Common Pitfalls to Avoid
Over-testing: A 2023 survey found neurologists order an average of 17.2 tests for possible MS, many with poor specificity that can lead to false positives, increased costs, and diagnostic delay 6
Confusing pseudoexacerbation with true relapse: Infection, fever, and metabolic disturbances cause temporary worsening without new inflammation. Always check for UTI and systemic infection before assuming true relapse
Unnecessary repeat CSF analysis: Oligoclonal bands do not change with disease activity and should not be repeated for monitoring 1, 3
Ordering biomarkers not ready for clinical use: While neurofilament light chain (NfL) and GFAP show promise for monitoring, they are not yet standardized for routine clinical decision-making in acute flares 7
Practical Algorithm
For established MS patient with acute symptom worsening:
First, determine if this is true relapse vs. pseudoexacerbation
- Check temperature, review for infection symptoms
- Order: CBC, urinalysis/culture
If considering corticosteroid treatment:
- Order: Basic metabolic panel, glucose
If presentation is atypical or diagnosis uncertain:
- Consider MRI with gadolinium (more useful than labs)
- Consider AQP4-IgG if spinal cord involvement is extensive
- CSF only if infection or alternative diagnosis suspected
Do NOT routinely order: ESR, ANA, thyroid function, vitamin levels, or repeat oligoclonal bands for established MS flares
The key principle: Laboratory testing during MS flares should be targeted to exclude mimics and ensure safe treatment, not to confirm the flare itself—that determination is clinical and radiological.