myelination disorders Flashcards
CNS myelin
oligodendrocyte- responsible for axon myelination in the CNS (analogous to schwann cell in the PNS), small round dark nulcei with short processes (oligo
Each oligodendrocyte provides a myelin sheath to several axons, a cytoplasmic process of the oligodendrocyte wraps around the axons and the external surfaces and cytoplasmic surfaces fuse
Myelin components- myelin basic proteins (MBP)- plasma membrane bound, proteolipid protein (PLP structural component of myelin
de and dys myelination
de myelination- destruction of myelin with relative preservation of axons- acquired disorders (ms, acute disseminated encephalomyelitis, central pontine myelinolysis, progressive multifocal leukoencephalopathy (PML), neuromyelitis optica (NMO)
Dysmyelination- failure to form myelin normally- leukodystrophy- discussed in metabolic disease session
MS
most common demyelinating disease of CNS, demyelination is multifocal (disseminated in space) and lesions are of different ages (disseminated in time), epidemiology- prevalence of approximately 1/1000 persons, W>M, peak age of onset 20-40, occurs more frequently in northern climes environmental etiology
Family twin/racial studies- familial rates, lowest in Af am, jap, chi, asians form ind pak
Ms classification
Classic type
Rapidly progressive types- Acute- marburg type, concentric sclerosis (Balos disease)
MS pathology
Grossly plaques of demyelination- depressed, irregular, firm (sclerosis- hard)
Usually occur in - periventicular white matter, optic nerves and chiasm, brainstem and spinal cord tracts, cerebellum, also occur in gray matter
types of MS plaques
active plaque- macrophages with myelin debris, perivascular lympocytes, reactive astrocytes, relative preservation of axons
Inactive plaque- few or no macrophages, few lymphocytes, myelin loss with axonal preservation, fibrillary astrocytes
Shadow plaque- partial myelin absence (either due to incomplete myelin loss or partial remyelination)
acute disseminated encephalomyelitis ADEM
monophasic demyelinating disease, acute onset, associated with recent viral illness, or immunization signs or symtoms occur 1-2 weeks following
also called perivenous encephalomyelitis and post infectious encephalomyelitis
headache lethagy and coma if diffuse brain involvement
80% complete recovery
Pathology- perivenous demyelination with axonal preservation, polymorphonuclear leukocytes PMNs early and lymphocytes later
Pathogenesis- immune response to pathogen associated antigens cross reacts to myelin ags that results in myelin damage
neuromyelitis optica, devic disease
relapsing synchronous bilaterl optic neuritis and spinal cord lesions, W>M, asians and af am >caucasians
Median age of onset is 39
path- necrosis- not just demyelination with inflammatory cells , Aquaporins (AQP4)- membrane water channels that help maintain astrocytic foot processes (autoantibodies induce complement- dependent cytotoxicity, leukocyte infiltration, cytokine release, and BBB breakdown), lead to oligodendrocyte death, myelin loss
AQP4 specific igG antibodies detectable in 60-90% of NMO pts
Central pontine myelinolysis (osmotic demyelination syndrome)
Monophasic process- loss of myelin with relative preservation of the axons and neurons in basis pontis–> limb weakness (quadriplegia), gaze / speech abn, dysphagia, hypotension, may affect extrapontine sites
Most commonly associated with too rapid correction of hyponatremia, associted with alcoholic liver damage, post liver transplant, chronic malcourishment/debilitation extensive skin burns
MS common problems
Optic neuritis is very common
Will not affect the peripheral nerves
Periventricular, juxtacortical, cortical infratentorial, sp cd invovlement are the most common
Autoimmunity in MS
Autoimmunity is a failure of an organism to recognize its own tissues as self which can lead to an immune response against its own cells and tissues
It is not known what triggers the onset of MS Genetic factors MHC, Environmental factors
B cell and T cell with blood brain disorder
Ms pathology
MS is believed to be driven by autoreactive CD4 T cells with specificity for antigens expressed by oligodendrocytes which comprise myelin, Myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG), proteolipid protein (PLP)
It is generally believed that myelin specific T cells get activated in the periphery then cross the BBB, where they are reactivated and initiates destruction, activation and expansion of autoreactive CD4T cells, breakdown of the BBB, infiltration of immune cells into the CNS, De myelination and remyelination, axonal and neuronal degeneration
T cells in MS
Strongest genetic risk facotr of development of MS is the MHC class 2 DR2 DRb1 1501 During activation differentiate into effector T cells
Th1 signiture cytokine is IFNy, Th17 cytokin is IL17A
B cells in MS
ectopic germinal centers
AStocytes that mess with BBB
Microglia damage and repair
Axonal loss and progression
axons actually die along with the demyelination
