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New Treatments for Entrapment Neuropathies

The facial nerves and peripheral cranial nerves can be studied. The facial nerve is probably the most common, and here we see a dramatic - not only slowing of motor conduction in the perineal nerves of this individual affected with Guillain-Barré - but a marked temporal dispersion of the muscle action potential, which should be a nice uniform diphasic potential as we are used to seeing. Here we see, because of segmental demyelination in the cranial nerve in this individual affected with a rather diffuse form of Guillain-Barré involving the cranial nerves, the phenomenon called temporal dispersion of the muscle action potential. That’s very characteristic of demyelinating disease. There’s no question that demyelination is occurring in Guillain-Barré.

In amyotrophic lateral sclerosis, because of the motor neuron disease, there is some transmissive defect in some patients with this condition. Certainly a more marked problem is with the loss of the anterior horn cell, but if the anterior horn cell is dying, in fact the synaptic efficiency deteriorates. We see here a decrement which may be nearing 10%, which is the limit that we set for that, and we see here it exaggerates much the way a myasthenia gravis patient would appear.

This brings us around to reminding you that the pathologies that underlie some of these abnormalities of motor or sensory conduction are of generally two basic types; one in which there is demyelination as a result of pressure, ischemia or metabolic disorder, toxic disorder, that will produce segmental demyelination and produce marked swelling of the motor or sensory conduction. Or there may be an axonal degeneration with loss of certain fibers, large fibers, producing a modest reduction in the motor or sensory conduction times. Wallerian degeneration is the kind of degeneration secondary to transection or injury that occurs at the distal axon.

The needle EMG shows us denervation of muscles. We see one here being examined with a concentric needle electrode, which would yield evidence - with the insertion of the needle - of the presence of motor unit potentials if the muscle is contracted. If the muscle is not contracting of course there is no motor unit activity. But these small biphasic, triphasic components are muscle action potentials, motor unit potentials, and these are quantifiable. Usually you range between 500 and 1,000 microvolts. There are spontaneous potentials we can find in muscles that have axonotmesis and degeneration. While we are in degeneration, this denervation activity which are fibrillations and positive waves, are very sensitive indicators of axonal disruption and degeneration. Vesiculations occur commonly. These are very large, almost single units firing abnormally during rest when they shouldn’t be firing and these vesiculations are a hallmark of motor neuron disease.

Repetitive discharges occur in certain metabolic disorders. Grouping of two or three motor units occur in thyroid disease and some individuals may show, in the course of a needle EMG study, muscle cramps which are really not specific or diagnostic. Here we see examples of insertional activity in a normal individual, and here in one who insertion is followed by a train of positive waves and fibrillation potentials characteristic of denervated activity. Here we see an unusual prolongation of the insertional activity called a myotonic discharge, and these are seen in certain myotonic dystrophies; myotonia congenita.

Here we see a patient with a needle insert here and a lot of increased insertional activity. Sometimes verging on myotonia, but certainly a lot of denervation potential. Small fragmented fibs and positive waves that we are seeing here regularly, and with contraction of very small duration, action potentials characteristic of a muscle disease; and in fact, the biopsy here shows this inflammatory myopathic changes with central nuclei and these tentorial changes that we see in the muscle fiber characteristic of an inflammatory myopathy with regeneration and degeneration of fibers side by side.

Be careful of the young mother who is in the third trimester and who is complaining of carpal tunnel symptoms and you are able to confirm that. I would follow, before offering surgery or intervening in that individual, I would wait until after delivery. Because it is remarkable how many carpal tunnels emerge during gestation, and in fact after delivery had resolved.