emg fundamental

Fundamentals of NerveConduction Studies & EMG

Goal of EDXGoal of EDX

Localization SeverityLocalization Severity

Muscle Nerve NMJMuscle Nerve NMJ

Fiber type Pathology Temporal CourseFiber type Pathology Temporal CourseSensory Axonal Hyper acuteSensory Axonal Hyper acuteMotor demyelinating AcuteMotor demyelinating AcuteMixed SubacuteMixed Subacute Acquired Hereditary ChronicAcquired Hereditary Chronic

Nerve Conduction Studies

A medical test where peripheral nerves are electrically stimulated and responses are recorded over nerve or muscle

Nerve Conduction Studies include

1) Routine Studies

A) Motor nerve conduction

B) Sensory nerve conduction

C) Late responses

2) Special Studies

Repetitive Stimulation, SSEP, MEP, VEP

Motor nerve conduction studies

1. Electrodes placed over muscle

2. Supra maximal stimulus applied over nerve to muscle

3. Compound motor action potential recorded (CMAP)

Motor nerve conduction studies

1. Stimulus repeated at second site

2. Second CMAP recorded

3. Distance measured between stimulation sites (cm)

Data reported for motor studies:

1. Distal latency

2. Amplitude of CMAP (each site)

3. Conduction velocity between sites

(calculated)

Data compared to normal data and

interpretation provided

Sensory nerve conduction studies

1. Electrode placed over sensory cutaneous

branch of nerve

2. Stimulus applied to nerve

3. Sensory nerve action potential recorded

(SNAP)

Late responses: F-waves

1. F-waves results from small number of motor neurons activated by antidromic

(back-firing)

2. Variable in amplitude and latency

3. Commonly minimum latency is measured

4.Supra maximal stimulus are applied

H ReflexH Reflex

1- It is a true reflex (it has afferent, synaps & 1- It is a true reflex (it has afferent, synaps & afferent pathway)afferent pathway)

2- Elicited by stimulation of tibial nerve & 2- Elicited by stimulation of tibial nerve & recording from soleus musclerecording from soleus muscle

3- Need sub maximal stimulation3- Need sub maximal stimulation

NCS: limitations

1. Painful stimulations

2. Temperature sensitive (S>M)

3. Assess mainly large fibers

4. Most useful for nerve conditions

Electromyography

Definition: A medical test where electrical

impulses are recorded from muscle at rest

and while contracting.

The recording is made by

1. needle – from a needle inserted in the

selected muscle

2. surface – from an electrode placed on the

skin over the selected muscle

Electromyography

1. Motor neuron or nerve diseases cause

larger units firing rapidly

2. muscle disorders give rise to smaller MUPs that fire early

NCS: Diagnostic Utility

1. Nerve diseases

2. Nerve root disease

3. Muscle disorders

4. Neuromuscular Junction disorder

Contra indication of NCS & EMGContra indication of NCS & EMG

1- Patient with artificial peacemaker1- Patient with artificial peacemaker

2- Patient with bleeding disorder2- Patient with bleeding disorder