Compressive and Demyelinating Disorders Flashcards
Demyelination can occur in:
a. peripheral nervous system only
b. central nervous system only
c. both
both
Demyelination in the central nervous system is…
damage to oligodendrocytes
Demyelination in the peripheral nervous system is…
damage to Schwann cells
what is the most common mechanism of injury for demyelination in the CNS?
damage to the processes, usually an autoimmune mechanism (multiple sclerosis)
what is the most common mechanism of injury for demyelination in the PNS?
○ Genetic deficits that impair the ability of Schwann cells to compact or produce myelin sheaths
○ Autoimmune – self-reactive antibodies, antibody complexes, or cytotoxic T-cells damage Schwann cells
what is multiple sclerosis?
immune-mediated disease directed against the CNS -> loss of myelin and eventual loss of axons
is multiple sclerosis more common in men or women?
3x more frequent in women
what is the peak incidence for multiple sclerosis?
between 20-40
true or false? * MS progresses straight to a chronic inflammatory picture with no preceding acute inflammation
true, typical of most autoimmune diseases
what are the 2 phases of MS
○ 1st phase (active plaques): presence of typical leukocytes found during chronic inflammation
▪ Destroy myelin and oligodendrocytes that form it, though new oligodendrocytes can still be generated
Major leukocytes:
* CD4+ Th (likely mostly Th1 and Th17) and B-cells
* Macrophages (recruited and derived from microglia) and cytotoxic T-cells
○ 2nd phase (inactive plaques): loss of axons (and eventually neurons) with limited to no leukocytic infiltration and prominent gliosis
explain active plaques
leukocytes are recruited from the circulation, across the BBB
Helper T-cells initiate an immune response against myelin (MBP which helps to compact the many layers of the myelin sheath)
These helper T-cells recruit other leukocytes into white matter (cytotoxic T-cells, macrophages) and activate them
- Cytotoxic T-cells seem to attack oligodendrocytes
* MBP-specific B-lymphocytes are also recruited into the CNS and produce anti-MBP antibodies – these also seem to help destroy the myelin sheath
what is a flare?
period of worsened neurological symptoms
what causes flares in MS?
Buildup of helper T-cells and cytotoxic T-cells in the CNS that attack white matter components and B-cells that produce myelin-specific antibodies
As flares continue, there seem to be areas where lymphocytes reside “permanently” these are called
lymphocytic follicles
where are the lymphocytic follicles most prominent?
around the meninges and blood vessels
what are inactive plaques
plaques without prominent inflammation
With loss of myelin and oligodendrocytes, axons tend to
degenerate
explain how the axons degenerate
- “destabilization” of action potentials
- Fewer action potentials -> reduced trophic support for neurons – leading to neuronal cell death
- Expression of NMDA receptors on “ naked” axons and calcium-mediated cytotoxicity – glutamate is also toxic to oligodendrocytes
Following demyelination, what happens to allow for action potential conduction
additional sodium channels are redistributed along the axon
what are the most common initial symptoms of MS
- paresthesia’s in one or more extremities, the trunk, or one side of the face
- Weakness or clumsiness of a leg or hand
- Visual disturbances
what is the L’hermitte’s phenomenon
Sensation of an “electrical shock” running down the back and along the limbs
what is Uhthoff sign which is very common in MS patients
a transient worsening of neurologic function (initially described as blurry vision after a hot bath), with heat exposure, physical exhaustion (exercise), infection, or dehydration
what is the symptom and history checklist called for clinical diagnosis of MS
MacDonald’s criteria
what is the treatment of MS
no cure, steroids can be used for acute flares, immunomodulators can be used for chronic treatment
