Sunday 28 September 2014

Multiple Sclerosis MRI

A 30 y o female with recent sudden onset double vision referred for MRI Brain and Orbit screening.
Neurological notes mentions left 6th CN palsy.

This MRI brain, sagittal FLAIR shows multiple linear T2 hyper intense foci involving corpus callosum and peri ventricular white matter aligned at right angle to lateral ventricle.
Optic nerve evaluation within normal limits.

Imaging diagnosis : Multiple sclerosis.

Multiple sclerosis (MS)

Probable autoimmune-mediated demyelination in genetically susceptible individuals.
The diagnostic clue is multiple perpendicular calloso septal T2 hyperintensities.

Characteristic locations are periventricular white matter, along deep medullary veins in more than 85%.
50-90% calloso septal interface.
Infra tentorial in 10% adults, more common in children.
Often bilateral and asymmetric. The T2 hyper intensities become confluent with severity.

Size, linear to small, ~ 5-10 mm, linear, round, or ovoid; "beveled", "target", "Dawson finger", "lesion-in-a-lesion" appearance. Tumefactive lesions can be large up to several cms can mimic neoplasm.
T2w images are more sensitive than FLAIR for posterior fossa lesions.
"Tumefactive" MS can mimic neoplasm.

On DWI, Acute lesions may show restricted diffusion, concentric ring pattern on diffusion-weighted
images with hyperintense rim.

Post contrast T1w, transient enhancement during active demyelination. More than 90% disappear within 6 months, may be nodular (68%) , ring (23%), Semilunar, incomplete, or "horseshoe-shaped"

MRS : Reduced NAA (NAA/Cr), increased Choline (Cho/Cr). MRS may allow early distinction between relapsing-remitting and secondary progressive disease.

Perfusion MRI (contrast-enhanced T2*) : Low rCBV

MR diagnostic criteria: 

  1. More than 3 discrete lesions more than 5 mm.
  2. Lesions in characteristic location.
  3. Compatible clinical history.

Nuclear Medicine PET: increased Glucose utilization correlates with I NAA in lesions.

Differential diagnosis: 

Viral prodrome, monophasic illness.
Autoimmune-mediated vasculitis
Enhancing lesions spare callososeptal interface
"Beaded" angiogram appearance.

Lyme disease
Can be identical to MS (skin rash common)

Susac syndrome
Clinical presentation, course different from MS
Classic triad :
1. Eephalopathy, memory loss, confusion.
2. Branch retinal artery occlusions
3. Hearing loss
Self-limited (2-4 y duration, then stabilizes), monophasic,
Multifocal supratentorial WM lesions, always involves CC.

General Features
o Unknown; increase incidence in first-order relatives.
o Gene transcripts present/increased in MS lesions
o Unknown; probably virus and/or autoimmune-mediated in genetically susceptible individuals
o Activated T-cells attack myelinated axons
o Cox-2, iNOS may cause excitotoxic death of oligodendrocytes
Estimated 2,500,000 people in world have MS
Most common disabling CNS disease of young adults; 1:1000 in Western world

Staging, Grading or Classification Criteria
Major clinical subtypes
1. Relapsing-remitting (RR) (85% initial presentation)
2. Secondary-progressive (SP) aka relapsing progressive
• By 10 years 50%, and by 25 years 90% of RR patients enter SP progressive phase.
3. Primary-progressive (PP) aka chronic progressive
• 5-10% of MS population progressive from start
4. Progressive-relapsing (PR)
• Rare, defined as progressive disease with clear acute relapses, with/without full recovery
• Periods between relapses characterized by continuing disease progression

MS variants/subtypes
1. Marburg type: Younger patients, febrile prodrome, clinically fulminant, death in months
2. Devic type ("neuromyelitis optica"): Simultaneous optic/spinal demyelination
3. Schilder type ("diffuse sclerosis"): Extensive, confluent, asymmetric demyelination bilateral supra-/infratentorial parenchyma.
4. Balo type ("concentric sclerosis"): Large lesions with alternating zones of demyelinated/myelinated white matter.

Clinical Presentation
Most common signs/symptoms
Variable; initially impaired/double vision of acute optic neuritis (50% with positive MR develop MS)
Weakness, numbness, tingling, gait disturbances
Decrease Sphincter control, blindness, paralysis, dementia
Cranial nerve palsy; usually multiple, 1-5% isolated (CNs 5, 6 most common)
Spinal cord symptoms in 80%

CSF positive for oligoclonal bands.

Age: 20-40; peak onset = 30; 3-5% < 15, 9% > 50
Adults: M:F = 1 : 1.7 to 2
Children/adolescents: M:F = 1 : 5 to 10
All groups but Caucasian most common
Most often occurs in temperate zones

Natural History & Prognosis: 
45% patients not severely affected, nearly normal
More than 80% with "probable" MS, positive MR progress to clinically definite MS
In early RR, recovery often complete
Majority: Protracted course with progression of deficits
Late: Severe disability, cognitive impairment.

Immunomodulators and /or immunosuppressant.

Insensitivity of FLAIR for infratentorial lesions

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