In a patient with clinically established multiple sclerosis and MRI lesions meeting dissemination‑in‑space criteria, what additional investigations are needed before starting disease‑modifying therapy?

Additional Investigations in Clinically Established MS with MRI Meeting DIS Criteria

In a patient with clinically established multiple sclerosis and MRI lesions meeting dissemination-in-space criteria, the critical additional investigation needed is exclusion of alternative diagnoses—this remains the cornerstone before starting disease-modifying therapy, even when imaging criteria are met 1.

Essential Diagnostic Algorithm

1. Rule Out MS Mimics (Mandatory)

The 2024 McDonald criteria explicitly state that exclusion of better alternative explanations for clinical or imaging findings is the key first diagnostic step 1. This is non-negotiable regardless of how convincing the MRI appears.

Specific investigations to exclude mimics:

• Serum testing for:

  • Anti-AQP4 antibodies (to exclude neuromyelitis optica spectrum disorder)
  • Anti-MOG antibodies (to exclude MOG antibody disease)
  • Vascular risk factors and inflammatory markers
  • Infectious serologies if clinically indicated

• CSF analysis when:

  • MRI findings are not entirely diagnostic 2
  • Features are unusual for MS 2
  • Patient demographics are atypical (older age, unusual presentation)
  • Diagnostic uncertainty exists despite meeting imaging criteria

2. Assess for Dissemination in Time (If Not Already Demonstrated)

Even with established clinical MS and DIS on MRI, you need evidence of DIT:

• Concomitant gadolinium-enhancing and non-enhancing lesions on a single scan fulfills DIT 1
• New T2 lesions on follow-up MRI compared to baseline 1
• CSF-specific oligoclonal bands can substitute for MRI evidence of DIT 2

3. Complete Anatomical Assessment

Brain AND spinal cord imaging is recommended at diagnosis 1:

• Whole spinal cord MRI to demonstrate additional lesions and support DIS
• Helps exclude alternative diagnoses (particularly important for distinguishing from AQP4+ NMOSD and MOGAD)
• Provides baseline for future monitoring

Optic nerve assessment (now the fifth anatomical location in 2024 criteria) 1:

• Fat-saturated MRI sequences if optic neuritis suspected
• Visual evoked potentials as alternative
• Optical coherence tomography (discussed in companion guidelines)

4. Advanced MRI Markers (When Available and Diagnostic Uncertainty Exists)

Susceptibility-sensitive imaging for highly specific MS markers 1:

• Central vein sign (CVS): Lesions with central veins are pathologically specific for MS
• Paramagnetic rim lesions (PRLs): Indicate chronic active inflammation specific to MS
• These can substitute for DIT or additional anatomical locations when conventional criteria are insufficient

Critical Pitfalls to Avoid

The major risk is overdiagnosis 2. The 2010-2024 McDonald criteria revisions increased sensitivity but created potential for false positives when:

• MRI findings are interpreted without pertinent clinical and laboratory information 2
• Radiologists lack expertise in recognizing the full range of abnormalities that support or refute MS diagnosis 2
• Non-specific white matter lesions (vascular, migraine-related) are misinterpreted as MS 3

A study of 220 patients referred for suspected MS based on incidental brain MRI findings found:

• Only 35.4% actually fulfilled McDonald criteria
• Only 8% had true radiologically isolated syndrome
• 97% of initially suspected cases were confirmed as non-MS after structured analysis 3

Baseline Investigations Before Starting DMT

Once MS diagnosis is confirmed:

1. Baseline MRI with gadolinium (brain and spinal cord) 1

   • Serves as reference for future monitoring
   • Documents disease burden
   • Informs prognosis

2. CSF examination (if not already done) 2

   • Particularly relevant when MRI is not entirely diagnostic
   • Oligoclonal bands support diagnosis
   • Helps risk-stratify patients

3. Screening specific to planned DMT:

   • JC virus antibody status if considering natalizumab 4
   • Hepatitis B/C, HIV, varicella zoster serology
   • Complete blood count, liver function tests
   • Cardiac evaluation for certain agents

When CSF Analysis Is Particularly Important

CSF testing is no longer required by 2010-2024 criteria for relapsing MS 2, but remains highly relevant in:

• Patients where MRI is not entirely diagnostic 2
• Atypical features or unusual presentations 2
• Primary progressive MS (helps support diagnosis) 5
• Older patients or those with vascular comorbidities
• When distinguishing from other inflammatory CNS disorders

The 2015 MAGNIMS guidelines explicitly state that CSF findings might be relevant in patients for whom MRI is not entirely diagnostic or reveals unusual features 2.

Bottom Line

Before starting disease-modifying therapy, you must:

1. Exclude alternative diagnoses (anti-AQP4, anti-MOG antibodies at minimum)
2. Confirm both DIS and DIT are met (or use CSF oligoclonal bands to substitute for DIT)
3. Obtain complete baseline imaging (brain, spinal cord, ± optic nerve)
4. Consider CSF analysis if any diagnostic uncertainty exists
5. Perform DMT-specific screening based on planned therapy

The emphasis has shifted toward earlier diagnosis, but diagnostic specificity must be maintained to avoid the serious consequences of misdiagnosis and inappropriate treatment with potentially harmful disease-modifying therapies 2.