Motor Nerve problems

Ayromlou H, Mohammad-Khanli H, Yazdchi-Marandi M, Rikhtegar R, Zarrintan S, Ej Golzari S, Ghabili K
Electrodiagnostic evaluation of peripheral nervous system changes in patients with multiple sclerosis.

There is supportive evidence that multiple sclerosis (MS) could potentially affect the peripheral nervous system. We assessed peripheral sensory and motor nerve involvement in patients with MS by a nerve conduction velocity test.
METHODS: We studied 75 patients who had a relapsing-remitting or secondary progressive pattern. We measured amplitude, latency, conduction velocity, Hoffmann reflex (H-Reflex), and F-Waves.
RESULTS:The amplitude of the right tibial, right proneal, left tibial, left proneal, and left median (leg) motor nerves was less than the mean for the normal population. Right ulnar (arm) sensory conduction in the patients showed an amplitude that was less than that of the normal population; there was no significant change in the amplitude of other sensory nerves. Latencies of the right and left median and right proneal motor nerves and left ulnar sensory nerves were statistically less than that of the normal population. Mean motor conduction velocity and F-wave conduction did not differ significantly from the normal population. H-reflex latencies of the right and left lower limbs were significantly more prolonged than those of the normal population.

CONCLUSION:Our results suggest possible peripheral motor nerve abnormalities in MS patients, especially with the amplitude of the motor nerves; however, our results do not demonstrate any significant difference among the nerve conduction velocity parameters of sensory nerves between MS patients and the normal population.

The H-reflex (or Hoffmann’s reflex) is a reflectory reaction of muscles after electrical stimulation of sensory fibres (Ia afferents stemming from muscle spindles) in their innervating nerves (for example, those located behind the knee). The H-reflex test is performed using an electric stimulator, which gives usually a square-wave current of short duration and small amplitude (higher stimulations might involve alpha fibres, causing an F-wave, compromising the results), and an EMG set, to record the muscle response. That response is usually a clear wave, called H-wave, 28-35 ms after the stimulus, not to be confused with an F-wave. An M-wave, an early response, occurs 3-6 milliseconds (thousandth of a second.. after the onset of stimulation. The H and F-waves are later responses. As the stimulus increases, the amplitude of the F-wave increases only slightly, and the H-wave decreases, and at supramaximal stimulus, the H-wave will disappear. The M-wave does the opposite of the H-wave. As the stimulus increases the M-wave increases. There is a point of minimal stimulus where the M-wave is absent and the H-wave is maximal.

H-reflex is analogous to the mechanically induced spinal stretch reflex (for example, knee jerk reflex). “The primary difference between the H-reflex and the spinal stretch reflex is that the H-reflex bypasses the muscle spindle, and, therefore, is a valuable tool in assessing modulation of monosynaptic reflex activity in the spinal cord.” Although stretch reflex gives just qualitative information about muscle spindles and reflex arch activity; if the purpose of the test to compare performances from different subjects, H-reflex should be used. In that case, in fact, latencies (ms) and amplitudes (mV) of H-wave can be compared.

H-reflex amplitudes measured by EMG are shown to decrease significantly with applied pressure such as massage and tapping to the cited muscle. The amount of decrease seems to be dependent on the force of the pressure, with higher pressures resulting in lower H-reflex amplitudes. H-reflex levels return to baseline immediately after pressure is released except in high pressure cases which had baseline levels returned within the first 10 seconds.

After about 5 days in zero gravity, for instance in orbit around Earth, the h-reflex diminishes significantly. It is generally assumed that this is due to a marked reduction in the excitability of the spinal cord in zero gravity. Once back on Earth, a marked recovery occurs during the first day, but it can take up to 10 days to return to normal. 

MS has been described as a CNS disease. Sensory nerves originate in the periphery and end up in the spinal cord. Motor nerves start in the CNS and contact the muscle. Nerve conduction studies showing a latency(delay)may suggest demyelination and loss of amplitude may reflect axon loss. In this study they found problems in the motor nerve pathways.

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