MULTIPLE SCLEROSIS;
It’s an Autoimmune Antibody mediated attack on Oligodendrocytes in the white matter of the Central Nervous System.
Myelin: within the CNS, it’s made by Oligodendrocytes while in Peripheral nervous system it’s made up of Schwann cell. So MS doesn’t affect peripheral nervous system. So MS should not affect spinal nerves or cranial nerves as they are part of peripheral nervous system. So lower motor type of involvement ( decreased reflexes, decreased tone etc) is not feature of MS. Remember optic nerve is an extension of brain & isn’t a part of PNS. Central connections of cranial nerves can be affected which will be counted as supra nuclear involvement.
Cell bodies of the neurons doesn’t have myelin, so cell bodies are no affected. Hence MS doesn’t affect grey matter or cranial nerve nuclei or anterior horn of spinal cord. As MS doesn’t affect cell bodies, so it can’t explain Seizures ( seizures are abnormal activation of cell bodies in grey matter).
MS is loss of Myelin sheath, so brain volume is not increased , so MS can’t explain raised ICP ( only exception is Tumourous variety of MS which can give mass affect & confused with SOL).
MS is damage to myelin sheath which can be regenerated. But the extent of regeneration may not be 100%, so recovery will be variable. Repeated damage to myelin sheath will cause cumulative damage & hence permanent neurological deficit. Also with repeated insults ( relapsing-remitting) to
Myelin sheath, axons get damaged as well. So repeated episodes of the attacks on myelin can cause permanent damage. Some time regeneration doesn’t occur , so damage is irreversible & progressive, rather than episodic. Sometime damage is slow & smouldering,so it presents as slowly progressive disease without any recovery.( primary progressive). So MS can be Relapsing-Remitting or
Relapsing-Remitting followed by Secondary Progressive, or Primary Progressive or Single Attack disease with no relapse.
Progressive means no regeneration of myelin causing permanent damage. Remitting means with repair of myelin sheath & some or complete recovery of the attack. To mart progressive means Progressive right from the first episode. Secondary progressive means that it was relapsing/ remitting to start with & later on changes to progressive pattern.
MS is Autoimmune disease mediated via antibodies produced by lymphocytes in brain; so CSF may have lymphocytes depending on the disease activity. However predominant findings will be elevated CSF globulins ( as its antibody mediated disease). Infective causes leak albumin, while immune causes raise globulins. This is also called albumin-cytological dissociation. These globulins will be oligoclonal ( infections has polyclonal while tumours has monoclonal globulins). Since its disease limited to CNS we don’t find oligoclonal bands in blood ( unlike some other disease)
Autoimmune diseases are more common in females of reproductive age due to abnormal MHC II ( HLA-D) which makes them prone to autoimmune diseases like MS etc. female sex hormones & natural tendency to tolerate foetal antigens also contribute to lose control on immune system. Being autoimmune disease role of immunosuppression is there.
Disseminated Sclerosis is another name of MS: Disseminated in time &/or place. So lesions can be scattered in various parts of the CNS ( disseminated in space). Some of these lesions may be clinically silent & may be detected by evoked potentials or MRI. Common sites are peri-ventricular, corpus callosum, cerebellum, brain stem, optic nerve, MLF,spinal cord ( but can be anywhere).
Disseminated in times means different areas of CNS affected at different times. So disease course is important to follow.
Sclerosis means Gliosis ( term used alternate to fibrosis in neurology) is replacement of demyelination areas by glial cells. These areas or demyelinated areas are detected as plaques on MRI,
MRI: T1 sees Myelin as white & grey matter as grey. T2 is opposite to T1, hence sees myelin as grey & nonyelin area as white. So demyelination lesions appear grey on T1 & white on T2. T2 FLAIR suppresses fluid & make demyelination bright.
Pan MRI from Brain to Spinal cord is needed to detect s the lesions disseminated in place including silent lesions is needed. Visual, somatosensory or auditory evoked potentials also help to detect uni ally silent lesions. CSF is helpful as stayed above.