Diagnostic Tests for Multiple Sclerosis (MS)
The diagnosis of multiple sclerosis requires a combination of clinical assessment, magnetic resonance imaging (MRI), cerebrospinal fluid analysis, and sometimes evoked potentials to demonstrate dissemination of lesions in both time and space. 1
Core Diagnostic Approach
No single test can definitively diagnose MS; diagnosis relies on demonstrating evidence of inflammatory-demyelinating injury within the central nervous system that is disseminated in both time and space 1, 2
MRI is the most sensitive and specific paraclinical test for MS diagnosis, showing characteristic lesions in the brain and spinal cord 1
Cerebrospinal fluid (CSF) analysis showing oligoclonal bands provides evidence of inflammation and immunological disturbance, particularly valuable when imaging findings are atypical or insufficient 1
Visual evoked potentials (VEP) can provide additional supportive evidence, especially when MRI abnormalities are few or have less specificity 1
MRI Criteria for MS Diagnosis
Brain and spinal cord MRI are used to demonstrate dissemination in space (DIS) and dissemination in time (DIT) of lesions 1
For dissemination in space, lesions must be detected in at least two of the following locations: periventricular, cortical/juxtacortical, infratentorial, or spinal cord 1
For dissemination in time, the presence of both gadolinium-enhancing and non-enhancing lesions on a single MRI, or a new T2 or gadolinium-enhancing lesion on follow-up MRI compared with baseline, is sufficient 1
Whole spinal cord imaging is recommended to define DIS, particularly in patients not fulfilling brain MRI criteria 1
Cerebrospinal Fluid Analysis
CSF analysis showing oligoclonal bands detected by established methods (preferably isoelectric focusing) that are different from any such bands in serum, or a raised IgG index, supports the diagnosis 1
CSF analysis is particularly valuable when clinical presentation is atypical or MRI findings do not fully meet diagnostic criteria 1
CSF results should be considered for clinically uncertain primary progressive MS cases 1
Other Diagnostic Tests
Visual evoked potentials showing delay with a well-preserved waveform can provide additional support for diagnosis 1
VEPs are particularly useful in situations with few MRI abnormalities or when MRI findings have less specificity (e.g., in older individuals with risk factors for microvascular ischemic disease) 1
Other types of evoked potential analysis contribute little to MS diagnosis 1
Diagnostic Categories
Following diagnostic evaluation, a patient is classified as having MS, "possible MS" (for those at risk but with equivocal evaluation), or "not MS" 1
The older terms "clinically definite" and "probable MS" are no longer recommended 1
Special Considerations
Diagnosis should be made with caution in patients with atypical presentations, such as those with dementia, epilepsy, or aphasia 1
Alternative diagnoses must always be considered, including other inflammatory demyelinating disorders, vascular, infectious, neoplastic, and metabolic conditions 3, 2
Biopsy is rarely needed but can confirm that a lesion is inflammatory and demyelinating, though it cannot on its own lead to a diagnosis of MS 1
The McDonald criteria have evolved over time to facilitate earlier diagnosis while maintaining diagnostic accuracy, with the most recent versions simplifying requirements for DIS and DIT 4, 5
Remember that MS diagnosis remains a partly subjective and partly objective process that is best made by an expert familiar with the disease and its differential diagnoses 1, 6.