Electrodiagnosis.doc - Electrodiagnosis Electrodiagnosis deals with the reaction of muscles and motor nerves to electrical stimuli The altered

Electrodiagnosis.doc - Electrodiagnosis Electrodiagnosis...

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Electrodiagnosis Electrodiagnosis deals with the reaction of muscles and motor nerves to electrical stimuli. The altered electrical reactions may aid in diagnosis, prognosis or therapy in pathological conditions of the motor tract including the brain, spinal cord, peripheral nerves and the muscles. Using the electrical reactions of nerves and muscles as aids in diagnosis, one must always put in mind that these tests are only part of the evidence. The other part is being supplied by the clinical examination of the muscular strength, reflexes and sensory condition of the affected region. A knowledge of the clinical pathology of the central and peripheral nervous systems is, therefore, equally essential for the proper interpretation of the findings. The motor point of a normal muscle is usually located near the origin of the muscle belly, where the motor nerve enters the muscle; this area known as the “end plate zone” . In the nerve trunk, the motor point can be found where the position of the nerve is nearest to the skin. There may be several points of maximal irritability in the course of a long nerve. In pathological conditions leading to a reaction of degeneration, the motor point of a muscle is displaced distally and the motor point of a nerve disappears entirely. 1
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1. Alternating Current / Direct Current Electrical stimulation generally refers to surface electrode techniques. It stimulates the superficial nerve fibers, which in turn leads to nerve trunk and motor point in the muscles. Testing with faradic stimulation and interrupted direct currents was widely used in the past but it is not very accurate. The faradic-type current provides impulses with a duration of 0.1-1.0 msec and a frequency of 50 - 100 Hz. Interrupted direct current was used in impulses with a duration of 100 msec, repeated 30 times / minute. Factors such as temperature, swelling, dry skin, pain and infection may inhibit excitation. This test distinguishes between normal and denervated muscles. It should be put into consideration that: - Normal musculature responds to electrical stimulation by either alternating current (AC) or direct current (DC). - A poor or absent response to AC stimulation indicates the presence of neural damage “reaction of degeneration” (RD). If this occurs, DC will be preferable. - Sluggish response with DC indicates moderate to severe damage to the nerve. - Absent response with DC indicates nerve section (absolute RD). Electrical reactions of muscles and nerves: RD Muscle / Nerve Faradic current Interrupted direct current Normal reaction Muscle Nerve Tetanic contraction Brisk single contraction Partial R.D. Muscle Nerve Diminished response Diminished response Sluggish contraction Full R.D. Muscle Nerve No response No response Sluggish response Absolute R.D. Muscle Nerve No response No response 2
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Course of RD: Whether it is partial or full, the course can be divided into: 1) The initial stage: Lasts from 10 days to 2 weeks. After the first week, the nerve looses all response to tetanic stimulation; the muscle responds
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