Peripheral Nervous System Flashcards
West Nile virus
- May infect lower motor neurons / anterior horn cells
- Type of arbovirus
- Most have no symptoms, but 20% have moderate to severe symptoms
- WNV can cause encephalitis or meningitis as well
- WNV meningitis is characterized by presence of a “coarse tremor” in upper extremities
Radiculitis
Inflammation of the spinal nerve roots
In the cervical spine, disk herniation affects the __.
In the lumbar spine, disk herniation affects the __.
In the cervical spine, disk herniation affects the lower of the two vertebral nerves (ex, a C3-C4 herniation affects C4).
In the lumbar spine, disk herniation affects the nerve below the level of the joint (ex, an L4-L5 herniation affects S1)
Spinal stenosis at the level of the cervical spine produces ___.
Spinal stenosis at the level of the lumbar spine produces ___.
Spinal stenosis at the level of the cervical spine produces symptoms of spinal cord compression at and below the level of the stenosis.
Spinal stenosis at the level of the lumbar spine produces cauda equina syndrome.
Carpal tunnel syndrome
- Compression of the median nerve within the carpal tunnel of the wrist
Cubital tunnel syndorme
- Compression of the ulnar nerve as it passes through the cubital tunnel of the elbow
Axonopathies
Glove and stocking distribution
Affect peripheral nerves in order of length
Myelinopathies
Demyelination
Affects peripheral nerves randomly
Myasthenia gravis vs Lambert Eaton myasthenic syndrome
In myasthenia gravis, the autoantibody target is ___. In Lamber Eaton myasthenia, the target is ___.
In myasthenia gravis, the autoantibody target is the acetylcholine receptor. In Lamber Eaton myasthenia, the target is the voltage-gated calcium channels.
Diagnosing myasthenia gravis
- Screen for anti-AChR and anti-Muscle-specific tyrosine kinase (MuSK)
- 90% of patients with systemic myasthenia have one, 50% of patients with ocular myasthenia have one
- Screen for thymoma
- Repetitive nerve stimulation test
- Amplitude of action potential decreases w/ repetitive stimulation
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Ice pack test
- If a patient has ptosis, leave an ice pack over eye for 2 min. Ptosis should go away if due to myasthenia gravis
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Endrophonium challenge
- Inhibits AChE, should temporarily alleviate symptoms.
Diagnosing Lamber-Eaton Myasthenia
- Screen for anti-VGCC
- Screen for neoplasia (especially small cell lung cancer)
- Repetitive nerve stimulation test
- Amplitude of action potential increases w/ repetitive stimulation
Long-term treatment of myasthenia gravis and Lamber Eaton myasthenia
- Remove thymoma, if present
- Treat cancer
- Neutralize autoantibody w/ plasma exchange or IVIg
- Long-term immunosuppression
- Prednisone or steroid-sparing agents
- For myasthenia gravis, pyridostigmine
- For Lamber-Eaton syndrome, 3,4-diaminopyridine
How does 3,4-diaminopyridine work?
It blocks the potassium channels on the pre-NMJ neuron, causing accumulation of positive charge as Ca2+ flows in through the free VACCs and facilitating ACh release to the NMJ.
Hints that weakness may be due to autoimmune disease at the NMJ
Fluctuating weakness with diurnal variation, which is sometimes temperature-dependent.
Findings on EMG
- Monitor at rest for fibrillation potentials, indicating irritability of the nerve likely due to nerve damage
- Monitor during action for motor unit potential analysis
- Damaged and irritable nerves will have much more jagged and higher amplitude impulses, as opposed to the slow and orderly impulses in an organized rhythmic contraction
Findings on Nerve conduction studies
- Amplitude correlates to # of functional neurons in the nerve
- Latency from initiation to peak. Surrogate for degree of nerve myelination.
- Repeat testing over different nerve segments, which may suggest very focal neuropathy that is likely due to compression.
Deep tendon reflex and nerves
A good way to track progress in patients being treated for myasthenia gravis
Monitoring the amount of ptosis in each eye
The muscles controlling ocular muscles are preferentially affected in myasthenia gravis. Ptosis and double vision are among the most common manifestations of the disease.
