Chapter 23 - Demyelinating diseases of the nervous system

Questions

Define the following terms:

demyelination, Guillain-Barre syndrome, multiple sclerosis, Schwann cell, oligodendrocyte, cytoalbuminologic dissociation.
Demyelination is an inflammatory attack on myelin.
Guillain Barre syndrome is a monophasic illness characterized by a cell-mediated immune attack on peripheral nervous system myelin.
Multiple sclerosis is a condition characterized by inflammatory, demyelinating lesions in the central nervous system separated in space and time.
The Schwann cell is the cell in the peripheral nervous system that creates myelin.
The oligodendrocyte is the glial cell in the central nervous system that creates myelin.
Cytoalbuminologic dissociation is the finding of high protein in the cerebrospinal fluid without many (usually less than 6) white blood cells. This is a characteristic of Guillain-Barre syndrome but is not completely diagnostic.


23-1. What is a good working definition of multiple sclerosis?

Answer 23-1. Multiple sclerosis is defined as multiple inflammatory white matter lesions separated in space and time.

23-2. What causes multiple sclerosis?

Answer 23-2. The cause is unknown although the rate is higher in certain families and certain genetic types. It is also higher in certain locations (particularly at higher latitudes), but where you spend your first 15 years appears to determine risk (higher the further away from equator). There is an immune attack on oligodendroglia, although the trigger is not clear.

23-3. Can a patient with a single episode of demyelination be diagnosed with MS?

Answer 23-3. Single episodes cannot be diagnosed as definite multiple sclerosis, although sometimes scans can detect evidence of prior as well as recent events that fulfill criteria.

23-4. What are the patterns of presentation for MS?

Answer 23-4. MS may be relapsing remitting, secondarily progressive, primary progressive or rapidly progressive.

23-5. What are common symptoms of MS?

Answer 23-5. Symptoms are scattered in the nervous system. They often affect optic nerves (vision loss), dorsal columns (loss of sensation), corticospinal tract (spastic weakness), cerebellar pathways (incoordination, dysarthria), medial longitudinal fasciculus (double vision on lateral gaze), spinal trigeminal tract (face numbness or pain) and control of the bladder. Lhermitte sign consists of an electric sensation down back and/or legs with neck flexion. This is due to irritation of cervical spinal cord sensory tracts.

23-6. Are certain portions of the nervous system not affected by MS?

Answer 23-6. MS does not directly damage neuron cell bodies and therefore does not result in basal ganglia symptoms. It does not result in LMN damage, damage to cranial nerve nuclei, or damage to peripheral nerves. It also does not produce aphasia or affect memory (until late in the condition).

23-7. What supportive tests are there for the diagnosis of MS?

Answer 23-7. There are many supportive tests for MS (none is perfect). MRI shows T2 and flair hyperintensities in periventricular distribution in well over 90% of patients. Some of these lesions may be enhancing (if they happened in the last 3 months). CSF shows oligoclonal bands and elevated IgG synthesis in over 80% of patients. Evoked potentials that may show problems with sensory systems that are not known from clinical exam. However, none of these (except serial MRIs) can show whether lesions are separated in space and time.

23-8. What other conditions can produce symptoms similar to MS?

Answer 23-8. You must rule out other conditions producing disseminated lesions such as lupus, Lyme, HIV, sarcoidosis, neurosyphilis, B12 deficiency, brucellosis, HTLV-1.

23-9. What is Guillain Barre syndrome (acute inflammatory demyelinating polyradiculoneuropathy - AIDP)?

Answer 23-9. Guillain-Barre syndrome is a monophasic demyelinating disease affecting peripheral nerves.

23-10. What causes Guillain-Barre syndrome?

Answer 23-10. Guillain-Barre syndrome may be triggered by certain infections. It is a cell-mediated immune attack on nerve roots with a lymphocytic infiltration in perivenous pattern.

23-11. What laboratory findings are supportive of the diagnosis of Guillain-Barre syndrome?

Answer 23-11. CSF shows high protein but few white blood cells (cytoalbuminologic dissociation).

23-12. What is the usual clinical picture for Guillain-Barre syndrome?

Answer 23-12. Symptoms develop over days to weeks, usually resolving over weeks to months. It often proceeds in an ascending fashion though it may even start in the cranial nerves. It can paralyze all muscles (including respiration) and produce autonomic nervous system instability. Reflexes are lost early on, even in clinically unaffected muscles. Autonomic instability can be fatal as can respiratory arrest, infection or pulmonary embolus. Guillain-Barre syndrome does not affect central nervous system. Patients usually recover (about 20% have residual).

23-13. What treatments help in Guillain-Barre syndrome?

Answer 23-13. Treatment with plasmapheresis or human immune globulin infusions may speed recovery. Steroids don't help the conditon.

23-14. What is chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)?

Answer 23-14. CIDP is a condition that has an appearance of chronic and demyelination of peripheral nerves. It is associated with subacute weakness and sensory loss and (as opposed to AIDP) responds to steroids and other immunosuppressives (including plasmapheresis and human immune globulin infusion).