Sample Outline: Electrodiagnosis

Electrodiagnosis

The detection of electrical reaction of muscles and nerves for diagnosis, prognosis and therapy by the use of electrotherapeutic current and electromyography. It is the study of electrical activity in motor units when stimulated by electrical pulses.

Uses:

1. Presence of normal and abnormal electrical excitability

2. Limits of pathology

3. Involvement of motor and sensory components

4. Presence of demyelination and axonopathy

5. Know the extent of pathological changes

Physiological Basis of Electrodiagnosis

1. Stimulation of Nerve Fibers

-Electrical potential of nerve is 90 mv

-demonstrates accommodation

2. Stimulation of Muscle fibers

- potential difference of 70 mv

3. Refractory Period- amount of time takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following an excitation

- absolute

-relative

4. Accomodation – the ability of the tissue to adapt itself to slowly increasing intensity

- Law of Dubois of Reymond

- in denervated muscle , it has lost power of accommodation except for long duration and slow rise peak intensities will be able to produce a brisk contraction

5. Action Potential

-impulse

-ability of a nerve and muscle membrane to develop transient changes in potential which is transmitted from one point to another

6. Reaction of Degeneration – the failure of the muscle to contract when stimulate by a tetanizing current

-Partial Reactioon of Degeneration

-Full/Complete Reaction of Degeneration

-Absolute Reaction of Degeneration

7. Polarity Reversal

Cathode is more effective in normal nerve, partial and complete denervation

Anode is effective in degeneration with atrophy

**sometimes in complete or partial denervation, the reverse may occur. Try both

Contraindications

1. Pacemakers/ patient depending on cardiac device

2. Over the carotid sinus

3. Abdominal area during pregnancy

Sites of Involvement

1. UMNL

2. LMNL

3. Neuromuscular Transmission Disorder

4. Myopathies

5. Functional Disorders

Clinical Applications

*Anterior Horn Cells

Poliomyelitis

Progressive Muscular Atrophy

ALS

Syringomyelia

*Nerve Root

Prolapsed

IV disc traction injuyry

Trauma

*Nerve Axon

Neuritis

GBS

*Myoneural Junction

MG

*Muscle Fibers

Myopathy

Dystrophy

*Plexus

Traction Injury

Wounds

Waveforms used in Electrodiagnosis

1. Rectangular

-Rheobase

-Chronaxie

-Nerve Excitability Test

-SDC

2. Rectangular and Triangular

- Galvanic/Faradic

Methods of Electrodiagnosis

1. Rheobase and Chronaxie Test

*Rheobase- measured using the cathode on the motor point of the nerve or bipolar technique

- it is the intensity of current needed to produce a minimal perceptible and palpable contraction

N ormal Value = 2-18 mA or 5-35 V

*Chronaxie- time necessary to induce minimal visible contractions with the stimulus twice the rheobase

Normal Values = < 1 ms

2. Pulse Ratio

- Ratio of the intensity of the current needed to produce a muscle contraction with 1 ms duration to that required if the duration of the pulse is 100 ms.

- A crude test:

Innervated- little or no difference but always lesser than 2.2:1

Denervated- > 2.5:1

Complete Degeneration- no response to 1

3. Nerve Excitability Test

- An electrical test which uses a short duration pulsed low frequency current to determine the state of excitability and conduction of a nerve trunk

- Performed 1 -2 days after onset of paralysis and repeated periodically

- Stimulating Points of Nerve Trunk

a. Facial Nerve- 3 branches are anterior to the mastoid

b. Erb’s points- lower inner angle of supraclavicular fossa

c. Ulnar nerve- upper point- above the medial epi of the elbow

Lower point- just above the wrist near the ulnar border

d. Radial Nerve- halfway down the arm posteriorly

e. Tibial Nerve- slightly above the center of the popliteal crease

f. Common peroneal nerve- medial to biceps tendon at the poplietal crease

g. Deep peroneal nerve- just behind of fibula

h. Superficial peroneal nerve- one cm below the deep peroneal nerve

4. Strength Duration Curve

- Intensity/time curve, intensity/duration curve

- A curve obtained by joining points that graphically represent the threshold values along the ordinate for various durations of stimulus displayed along abscissa

5. Reaction of Degeneration Test

-a gross screening test to differentiate a muscle with (N) peripheral innervations from a muscle with peripheral denervation

- done 10 days after the onset of the problem

-aka Galvanic Faradic Test

6. Nerve Conduction Test

-asses the time and quality of the conduction of neural impulses In peripheral motor and sensory nerves

Reference: Electrophysical Agent by Wadsworth