1
Q
Electrodiagnostics
A
- it is a method of obtaining information about diseases by passively recording the electrical activity of body parts or by measuring their response to external electrical stimulus.
- is a branch of medical practice in which electrical tests are performed to evaluate excitability of nerves and muscles using DC and PC.
- The aim of electrodiagnositcs is to demonstrate the changes in excitability, occuring in the neuromuscular system which is sick
2
Q
Electrodiagnostic testing
A
- Is a powerful tool for diagnosing and developing treatment plans for patients with diseases of the peripheral nervous system and muscles
3
Q
The Electrodiagnostic examinations
A
- can provide essential information in cases of suspected peripheral nervous system disorders or injury
4
Q
Electrical stimulation should not be used under 3 conditions
A
- with patients having a pacemaker
- over the carotid sinus
- over the abdominal area during pregnancy
5
Q
Qualitative techniques
A
- involve observation of a type of muscle contraction in response to specific electrical pulses
6
Q
Quantitative Techniques
A
- are based on a quantitative determination of physical quantities, which are measurement of muscle excitability. Examples: strength-duration curve, chronaxie measurements
7
Q
Motor point
A
- a small area overlying muscle where aslight visible contraction is most easily elicited with a minimal amplitude(intensity) electrical stimulus
8
Q
A motor point of a nerve
A
- corresponds to a point on the skin, at which a nerve lies closest to skin surface
9
Q
A motor point of a muscle
A
- a point where a nerve enters into a muscle
10
Q
Traditional clinical electrical evaluation tests
A
- Reaction of degeneration test(RD)
- Strength-duration curve and chronaxie test
- nerve conducting tests
- clinical electromygraphy(EMG)
11
Q
Reaction of degeneration test(RD)
A
- This tests is a useful screening procedure for assessment of problems that may involve lower motor neurons
- Reaction of normally innervated muscle=it will respond with a brisk twitch when stimulated with a short-duration pulse lasting less than 1 ms and also when stimulated with longer pulse durations (for example 100 ms)
- Reaction of normally innervated muscle- it will respond with sustained or tetanic contraction if the pulses are applied in rapid succession
- Reaction of a muscle with peripheral denervation - it will not respond to a stimulus of 1 ms or shorter but will contract in a sluggish manner when the longer pulse duration stimulus is applied
12
Q
RD Test - using electrodes
A
- The electrode is used to search as precisely as possiible or the motor point of the muscle of interest
- The negative(cathode) electrode- is used as the active stimulating electrode over the motor point
13
Q
The first part of Classical RD test
A
- the motor point area is stimulated with a series of short-duration(less than 1ms) pulses
- a frequency of the stimulus-greater than 20Hz (a tetanic or sustained contraction)
- a waveform- monophasic or biphasic(assymmetrical)
14
Q
Reaction of a muscle in the first part of the classical RD test
A
- a tetanic contraction- a muscle is normally innervated
- a sluggish response or no response- peripheral denervation is likely to occur
15
Q
The second part of the classical RD test
A
- the involved muscle is stimulated with a long-duration pulse
- a monophasic pulse of atleast 100 ms duration or preferably longer
16
Q
Reaction of a muscle in the second part of the classical RD test
A
- a slow or sluggish response-contractile muscle tissue is present but the muscle is either partially or completely denervated
17
Q
Reaction of degeneration test(RD)-Part 2
A
- The RD test is usually not done until atleast 10 days after onset of the problem, so that the process of neural degenration can progress to a stage in which electrical changes would appear
- An abbreviated form of the test for reaction of degeneration may be used as a quick screening test for differentiating a muscle with normal peripheral innervation from a muscle with peripheral denervation
- The RD test is only a gross screening procedure and should not be expected to differentiate or precisely identify the location of pathology. The test may be indicated in conditions of unexplained paralysis
18
Q
Strength - Duration Curve and Chronaxie test
A
- 1930-1960 - strength - duration curves and chronaxie measurements were widely used for electrodiagnosis of peripheral nervous system disorders in these years
- Their frequency of use sharply declined with the development of nerve conduction testing and electromyography
- Three tests provide a reliable means of assessing the locatio,n, severity and progress of peripheral nerve - nerve degeneration and regeneration
19
Q
Chronaxie
A
- a minimal pulse duration of stimulus of twice rheobase strength that will cause the excitable cell membrane to discharge
20
Q
Strength - Duration Curve
A
- is obtained by imposition of values of the time and values of the intensity which produce the minimal muscle contraction in the coordinate system
- Plotting an S-D curve requires pulse duration ranging from 0.01 ms to 1000ms
- To plot the strength - duration curve rectangular pulses are use
21
Q
Rheobase
A
- a minimal intensity of stimulus amplitude(strength) required to eleicit a minimal visually perceptible muscle contraction (for 1000 ms impulse)
22
Q
Strength - Duration Curve Uses
A
Can be used for:
- evolution of variety of lower motor neuron pathologies
- Assessment of peripheral nerve injuries
These tests can provide reliable and accurate information on the status of peripheral innervation and denervation
23
Q
The intensity of the Stimulus (criteria of the intensity (amplitude) or strength and pulse duration or time of the stimulus)
A
must be strong to depolarize the membrane to its threshold level for excitability
24
Q
Time of the stimulus ( criteria of the intensity(amplitude) or strength and pulse duration or time of the stimulus)
A
the stimulus be of suffiecient duration to overcome the capacitance of the membrane
Q= i• t= constant
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To plot the strength- duration curve
* triangular pulses can be used
* using progressively shorter pulse durations , the values of stimulus amplitude which produce a minimal muscle contraction are recorded and then plotted on the graph
* chronaxie and rheobase can be determined from S-D curve
* Chronaxie
* 0.1-1ms (a muscle is normally innervated)
* 30-50ms ( fully denervated muscle)
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Strength- Duration Curve and Chronaxie Testing:
- Are as objective as nerve conducting testing and electromyography
- are non-invasive
- can provide valuable information on the status and progress peripheral nerve injuries
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Strength- Duration Curve and Chronaxie Testing, other applications:
- Can be for evaluation of peripheral neuritis, other peripheral nerve disease that may involve axonal degeneration and motor-neuron disease conditions
- the tests may be used to complement other evaluative procedures in differentiating between normal nerve tissue and neuropathology
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Electromygraphy (EMG)
* an assessment which provides a means of monitoring and evaluating electrical activity of muscle directly-without artificial stimulation
* advantage: characteristics of muscle can be studied during relaxation and voluntary contraction
* useful in evaluating electrical activity of lower motor neurons and muscle fibers, because electromygraphy helps in identifying electrical changes consistent with pathologic processes in these anatomic areas
* instrumentation required is similar to what is used in nerve conduction testing, but an electrical stimulator is not needed
* a sterile needle electrode is inserted directly into the muscle
* endogenous electrophysiologic activity produced by depolarization and repolarization of the muscle cell memebrane is transduced from the electrode and displayed on oscilloscope
* monopolar and concentric needle electrodes are most commonly used in routine EMG
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Electromygraphy (Electromygraphic activity is studied under the following conditions)
* while the muscle is at rest and is completely relaxed
* during a mild contraction, just strong enough to produce individual motor unit action potentials
* during a very strong contraction, held with enough force to recruit as many motor units as possible
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**Nerve Conducting Tests**: Purpose
- The purpose of these tests is to assess the time and quality of the conduction of neural impulses in peripheral motor and sensory nerves
- A controlled monophasic pulsed electrical stimulus is applied to the skin overlying a nerve
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**Nerve Conducting Tests**: Instrumentation
- a differential amplifier capable of detecting and accurately amplifying signals in a range from 2 mV to 50 mV
- an electrical stimulator that provides square wave monophasic pulsed stimulus from 0.05 to 1 ms, and output amplitude up to 500 V or 100 mA
- an oscilloscope
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**Nerve Conducting Tests**: Responses
- the stimulus frequency capability should be variable from signal to pulse trains of 50 Hz
- The responses are recorded from the specific sites of interest, which may be from:
\>Muscle in the motor nerve conduction tests
\>peripheral sensory nerves
\>the scalp in evokes potential studies
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**Nerve Conducting Tests**: Tests
The following tests are distinguished:
-motor nerve conduction
-f wave nerve conduction
-sensory nerve conduction
-h reflex response
These tests are useful in establishing or rulingout the presence of a peripheral neuropathy and determining and localizing a peripheral nerve entrapment or a plexopathy
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**Nerve Conducting Tests**: Another Feature of Assessment
Another Feature of the assessment of nerve conduction test results is differentiation, when possible between nerve conduction changes consistent with a demyelinating process and those seen with an axonal disorder.
