Demyelinating diseases of the CNS (Week 3--Vinters) Flashcards
Multiple Sclerosis epidemiology
Demyelinating disease of the CNS (most common)
Young adults 20-40 years old
Females more
How do you diagnose MS
No single diagnostic test for MS
Clinical diagnosis supported by laboratory testing
CNS lesions in more than 1 neuroanatomic location and on more than 1 occasion
MRI, evoked potentials (visual, somatosensory and brain stem), CSF analysis (IgG synthetic rate, more commonly, oligoclonal bands)
Patient may be given diagnosis of clinically definite MS, laboratory-supported definite MS, clinically probably MS or laboratory probably MS
Clinically definite MS
2 attacks and clinical evidence of 2 separate lesions
OR
2 attacks, clinical evidence of 1 lesion and laboratory evidence of another lesion
Laboratory-supported definite MS
2 attacks, either clinical or laboratory evidence of one lesion and CSF IgG or oligoclonal bands
OR
1 attack, clinical evidence of 2 separate lesions and CSF IgG or oligoclonal bands
OR
1 attack, clinical evidence of 1 lesion and laboratory evidence of another and CSF IgG or oligoclonal bands
Clinically probably MS
2 attacks and clinical evidence of 1 lesion
OR
1 attack and clinical evidence of 2 separate lesions
OR
1 attack, clinical evidence of 1 lesion and laboratory evidence of another
Laboratory-supported probably MS
2 attacks and CSF IgG or oligoclonal bands
Note: 2 attacks must involve different parts of the nervous system, must be separated by one month and must have each lasted at least 24 hours
Expanded Disability Status Scale (EDSS)
Grading scale to document disability in an MS patient
Ranges from 0 (normal exam) to 10 (death due to MS)
- 5 means minimal disability in 2 functional systems
- 5 means requirement for constant bilateral assistance (canes, crutches, braces) to walk about 20 meters; severe disability in 2+ functional systems
Documentation that patient’s EDSS score is increased from one exam to the next is objective marker for disease progression
Possible clinical courses of MS
Most (85%) begin with relapsing-remitting course which then gives way to secondary chronic progressive course (gradual increase in EDSS score but no more abrupt relapses)
Primary progressive course unusual and never associated with abrupt relapses (occurs in men with later onset of disease, 40+ years old)
Neuropathologic lesions found within the CNS of MS patients
Usually patient will have both acute and chronic lesions at any given time
Acute: active inflammation (usually around venules) involving T lymphocytes and macrophages; demyelination with phagocytosis of myelin debris
Chronic: no infiltrative lymphocytes or macrophages, devoid of myelin at center, astrocytic proliferation and hypertrophy (astrogliosis) within centers and at periphery of demyelinating plaques, evidence of abortive attempts at remyelination found as sparse thin rims of myelin around axons
General appearance of brain slice of patient with MS
MS plaques are well demarcated regions of demyelination with relative preservation of underlying axons (gelatinous areas surrounded by normal white matter)
Are axons preserved in MS?
Used to be thought that axons were spared but recent data shows that there is significant axon loss
Pathogenesis of axonal injury not known but may be causesd by sustained influx of Na+ then Ca2+ into axons/neurons
Rare variants of MS
Balo’s concentric sclerosis: concentric alternating bands of demyelinated/myelinated white matter
Fulminant/acute MS/Marburg variant: mass lesion
Devic’s disease/neuromyelitis optica: demyelination in optic nerve and spinal cord; AQP4 autoantibodies (often simultaneous)
Does MS affect white or grey matter?
Of course affects white matter tracts but affects gray matter too, including cerebral cortex which may contribute to cognitive impairment
Note: not all people with MS get cognitive impairment, but IF there is cortex affected then they will
Genetic and environmental causes of MS
We don’t know the etiology of MS!
Evidence for genetic causes: disease associated with immune response genes (HLA); increased risk for 1st degree relatives and more in monozygotic twins
Evidence for environmental causes: outbreaks of MS when immigrants come in; geographic distribution not uniform–less around equator; kids migrate before 15 adopt risk of region they migrated to but after 15 keep home risk (maybe environmental agent acts on developing immune system)
Is there an asociated infectious agent for MS?
No single agent associated with MS
May be that we haven’t found it/them yet and may be that there is none
Broad immunosuppressive therapy is beneficial in MS (maybe not a causative agent)
Maybe various viruses activate autoimmunity to myelin in nonspecific ways
Experimental autoimmune encephalomyelitis (EAE)
Animal model for MS
EAE in SJL strain of mice is particularly useful as MS model since is characterized by relapsing remitting disease course with gradual progression
Mice immunized with myelin proteion (MBP) so create antibodies to MBP –> after 10-14 days are sacrificed and draining lymph node cells (LNCs) placed in culture with MBP (LNCs will attack MBP, and be “MBP stimulated LNCs”) –> MBP stimulated LNCs transferred to naive recipient mouse (LNCs attack naive mouse’s MBP) –> mice develop inflammatory demyelinating lesions within the CNS 7-10 days after transfer
What types of cells are necessary for the transfer of disease in EAE?
CD4+ lymphocytes that are specific for myelin proteins MBP, PLP, etc (if specific for ovalbumin, disease will NOT be transferred)
What must the myelin specific T lymphocytes produce to transfer disease?
T lymphocytes must produce TH1 cytokines (IFN gamma, TNF) upon activation with antigen
Probably because these cytokines act on endothelial cells of BBB to increase permeability and permit entry of immune cells from blood into CNS (possibly a key initiating event in MS)
Note: TH2 cytokines are protective
Full explanation of immunopathogenesis of MS
CD4+ myelin protein specific circulating T lymphocytes are in activated state –> produce TH1 cytokines (IFN gamma, TNF) –> cytokines cause opening of BBB –> T lymphocytes and macrophages enter CNS and cause inflammation and myelin injury –> demyelination
Not clear how axonal injury occurs
Use of MRI in neuro-imaging MS
Serial MRIs show that MS lesions appear and/or enlarge even when patient is clinically stable
Gadolinium enhancement on T1 images indicates areas of active inflammation as lymphocytes and macrophages open the BBB early in lesion development
T2 images show enlarging lesions and atrophy, axonal loss late in disease process
Patient will have heterogeneous picture of lesions with some actively inflamed and others chronic and associated with gliosis and axonal loss
Progression shows less gadolinium enhancement and more atrophy on MRI
MS treatment
Acute: solu-medrol followed by prednisone taper over 2 weeks
Prophylaxis: interferon beta, IFN-1b, Betaseron; interferon beta, IFN-1a, avonex; copolymer 1 (copaxone), glatiramer acetate
Non-MS demyelinating lesions (rare)
Leykodystrophies
Progressive multifocal leukoencephalopathy (PML)
Central pontine myelinolysis (CPM)
Acute disseminated encephalomyelitis (ADEM)
Leukodystrophies
Dysmyelinating disorders
Rare, usually present in infants and children but sometimes adults
Progressive neurologic decline with spasticity
Result from breakdown of abnormally formed myelin
Most cases due to well-characterized genetic abnormalities of enzymes important in forming and maintaining normal CNS myelin
Neuropathology shows diffuse white matter pallor, brain atrophy, affects both cerebral hemispheres symmetrically
VERY rare
Progressive multifocal leukoencephalopathy (PML)
Destructive myelin lesions usually asymmetrical within cerebral hemispheres
Unlike MS because show patchy “moth-eaten” areas of myelin (poorly demarcated regions) with cystic areas of injury (may look like infarct) and myelinated fiber loss (can also involve brainstem and cerebellum) caused by opportunistic infection of the brain by papovavirus (JC virus) in immunosuppressed patients
Most commonly seen in AIDS patients
Rare
Central pontine myelinolysis (CPM)
Central region of well demarcated demyelination in mid-pons, and axonal injury in severe cases
Linked to rapid correction of severe hyponatremia (“osmotic demyelinating syndromes”)
Brainstem of 8-10% of orthotopic liver transplant patients in autopsy
Clinical correlates not well characterized, but probably flaccid quadriparesis if corticospinal tracts (pass thru basis pontis) affected
In some, can be shown by MRI and is reversible
Toxic leukoencephalopathies result from action of toxins on CNS myelinated axons (recreational drugs or chemotherapeutic agents)
Softening of area by palpation on autopsy specimen if severe
Acute disseminated encephalomyelitis (ADEM)
Occurs a few weeks after vaccination or systemic viral infection
Resolves 1-6 months
Neuropathologically perivenous areas of demyelination throughout CNS and variably extensive lymphocytic infiltrates
Probably clinically reversible
No macroscopic changes on gross inspection of brain, only congested blood vessels and questionable areas of demyelination
Very rare
How is spinal cord affected by MS
Spinal cord is affected by MS
MS plaques do NOT respect tract boundaries (it is NOT Wallerian Degeneration)
Just get demyelination of a big part of the spinal cord including many different spinal tracts
