Diagnostic Criteria for Multiple Sclerosis

Imaging Requirements

The American Academy of Neurology recommends a standardized brain MRI protocol including axial T1-weighted sequences before and after contrast, axial T2-weighted and proton-density (or T2-FLAIR) sequences, and sagittal 2D or isotropic 3D T2-FLAIR sequences, with a single dose of gadolinium-based contrast and a minimum 5-minute delay after injection 1
A 1.5T or 3.0T scanner with 3D acquisitions or 2D with 3-mm thick slices and no gap is recommended for brain MRI 2
Spinal Cord MRI should include sagittal imaging with dual-echo (proton-density and T2-weighted) conventional/fast spin-echo, STIR (alternative to proton-density-weighted), and contrast-enhanced T1-weighted spin-echo (if T2 lesions present), and should cover cervical, thoracic, and lumbar regions 1, 2

The National Multiple Sclerosis Society recommends requiring at least 3 of the following 4 criteria: one or more gadolinium-enhancing lesions or nine T2-hyperintense lesions, one or more infratentorial lesions, one or more juxtacortical lesions, and three or more periventricular lesions 3
The McDonald criteria require demonstration of lesions in the central nervous system with dissemination in space (DIS) and time (DIT), with no better explanation for the clinical presentation, and are supported by guidelines from societies such as the National Multiple Sclerosis Society, with a strength of evidence considered high for these diagnostic criteria 3, 4
The diagnostic evaluation of MS should include evaluating clinical presentation for typical MS symptoms, performing MRI of brain and spinal cord, considering CSF analysis when MRI findings are insufficient or atypical, and performing VEP if necessary, with the goal of demonstrating DIS and DIT, as supported by the Annals of Neurology in 2001 3
The following table outlines the McDonald criteria for MS diagnosis based on clinical presentation:

Clinical Presentation	Additional Data Needed for MS Diagnosis
Two or more attacks; objective clinical evidence of 2+ lesions	No additional tests required
Two or more attacks; objective clinical evidence of 1 lesion	DIS by MRI or 2+ MRI lesions consistent with MS plus positive CSF
One attack; objective clinical evidence of 2+ lesions	DIT by MRI or second clinical attack
One attack; objective clinical evidence of 1 lesion	DIS by MRI or 2+ MRI lesions plus positive CSF AND DIT by MRI or second attack
Insidious neurological progression suggestive of MS	DIS by specific MRI criteria AND DIT by MRI or continued progression for 1 year [3, 4]

For patients aged >50 years or with vascular risk factors, more stringent criteria (e.g., higher number of periventricular lesions) should be considered 2
In pediatric cases (especially <11 years), special care is needed in interpretation 2
A lesion in the optic nerve is added as an additional central nervous system area for DIS criteria 4
DIT can be demonstrated by a new T2 or gadolinium-enhancing lesion on a follow-up MRI compared to a baseline MRI, or the simultaneous presence of gadolinium-enhancing and non-enhancing lesions at any time point, as recommended by the International Panel on the Diagnosis of Multiple Sclerosis 3
The following table outlines differential diagnosis for various clinical presentations:

Type	Differential Diagnosis	Additional Testing
Limbic encephalitis	HSV, VZV, HHV6	CSF viral PCR, CSF VZV IgG/IgM
Cortical/subcortical	ADEM, tumefactive MS, CJD	MOG-IgG, CSF JCV PCR, CSF prion panel
Striatal encephalitis	CJD, WNV, toxic encephalopathy	Prion panel, WNV IgM, toxicology screen
Brainstem encephalitis	Listeria, viral, CLIPPERS	CSF bacterial culture, viral PCR [5]

VEPs are highly valuable for detecting demyelinating lesions in the optic pathways, with delayed P100 latency being a sensitive indicator of demyelination, and can detect subclinical optic nerve involvement even when routine ophthalmological examinations are normal, as supported by the American Academy of Neurology 3
VEPs are useful in monitoring diseases that can affect the visual pathways, such as optic neuritis, compressive lesions, toxic and nutritional optic neuropathies, and hereditary optic neuropathies, as recommended by the International Society for Clinical Electrophysiology of Vision (ISCEV) 6
Cerebrospinal fluid analysis can provide supportive evidence for the immunological and inflammatory nature of the lesion(s) when MRI criteria are not sufficient, MRI findings are non-specific, or the clinical presentation is atypical, as recommended by the National Multiple Sclerosis Society and International Panel on MS Diagnosis 3

MS must be distinguished from conditions that can mimic its clinical or radiological features, including hypoxic-ischemic vasculopathy, inflammatory diseases and vasculitis, non-MS idiopathic inflammatory diseases, toxic, metabolic, and infectious diseases, and neuromyelitis optica spectrum disorders, as emphasized by the Annals of Neurology in 2001 3
The diagnosis of MS remains partly subjective and partly objective, and is best made by a neurologist with expertise in MS who is familiar with the disease, its differential diagnoses, and the interpretation of paraclinical assessments, as recommended by the International Panel on MS Diagnosis 3
Biopsy is rarely needed but can confirm inflammatory demyelination when diagnosis remains uncertain despite thorough evaluation, according to the International Panel on MS Diagnosis 3
The diagnostic process should be thorough, as MS is a diagnosis with significant implications for treatment and prognosis, with an overall life expectancy less than the general population, as suggested by the National Institute of Neurological Disorders and Stroke 3