Dr Moizuddin Khan Dr Beenish Mukhtar EMG and NCV Dr Moizuddin Khan Dr Beenish Mukhtar

Electrodiagnosis Electrodiagnostic (EDX) studies play a key role in the evaluation of patients with neuromuscular disorders. Among these studies are nerve conduction studies (NCV), repetitive stimulation, late responses (F-wave and H reflex), SSEP, blink reflexes and needle electromyography (EMG), in addition to a variety of other specialized examinations.

NCV’s and EMG NCV’s and needle EMG form the core of the electrodiagnostic study. These studies are performed first and usually yield the greatest diagnostic value. Performed and interpreted correctly, these studies yield critical information about underlying neuromuscular disorders . These are designed to investigate and diagnose the functioning of the nervous system

What is an NCV NCV, or Nerve Conduction Velocity, is an electrical diagnostic test that provides information about abnormal conditions in the nerves. Nerves are stimulated with small electrical impulses by one electrode while other electrodes detect the electrical impulse "down-stream" from the first electrode.

NCV wave form may look like this

Interpreting NCV When interpreting NCV, the distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission. Slower than normal speed could indicate nerve damage from direct trauma, demyelination, diabetic or peripheral neuropathy, viral nerve infection or nerve entrapment diseases like the Carpal Tunnel Syndrome among other conditions.

What is EMG? EMG, or Electromyography is a technique for evaluating and recording the electrical activity produced by muscles. An electromyogram detects the tiny amount of electricity generated by muscle cells when they are activated by the nerves connected to them.

Types of EMG There are two types of EMG: intramuscular EMG and surface EMG. The intramuscular EMG is the most common. It involves inserting a needle electrode through the skin into the muscle that is being studied. Surface EMG (SEMG) involves placing electrodes on the skin over the muscle to detect the electrical activity of the muscle. It is not used as often because it provides less useful information than the intramuscular EMG.

EMG EMGs can detect abnormal muscle electrical activity in many diseases and conditions, including inflammation of muscles, pinched nerves, damage to nerves in the arms and legs, disc herniation, and degenerative diseases such as muscular dystrophy and Myesthenia gravis, among others. The EMG helps doctors distinguish between muscle conditions that begin in the muscle and nerve disorders that cause muscle weakness.

EDX supports dx and appropriate care The information gained from EDX studies often lead to specific treatment strategies, medical treatment or surgery.

EDX support your clinical examination In practice, EDX studies serve as an extension of the clinical examination and should always be considered as such.

EDX Quantitates Nerve and/or Muscle Injury Provides Useful Data Regarding Nerve Injury Site Type Severity Duration Prognosis

Goals of EDX Testing | | Location Severity | | Location Severity ________|____________|_________ | | | | Muscle NMJ Nerve Anterior Horn

Nerve Conduction Studies Studies of the waveforms generated in the peripheral nervous system. – Motor nerve conduction (CMAP) Stimulation of a peripheral nerve while recording from a muscle innervated by that nerve. Sensory nerve conduction (SNAP) Stimulation a mixed nerve while recording from a mixed or cutaneous nerve

Terminology LATENCY (DL) Interval between the onset of a stimulus and the onset of a response. AMPLITUDE (AMP) The maximum voltage difference between two point. It is proportional to the number and size of nerve fibers that are depolarized. Provides an estimate of the amount of nerve tissue that is electrically active DURATION The time from onset to termination. Total duration measures the dispersion of all components. Measures the differences in conduction of the nerve fibers CONDUCTION VELOCITY (CV) The “speed” at which the nerve fibers are carrying the electrical stimulus between two sites. Comparison of conduction between two segments of the same nerve can localize a lesion.

Types of nerve conduction studies Sensory: typically antidromic - Commonly examined nerves: Sural, ulnar, median, occasionally radial, superficial peroneal or lateral femoral cutaneous nerve.

Sensory NCS Parameters Onset and peak latencies Conduction velocity determined by velocity of a very few fast fibers Amplitude determined by the number of large sensory fibers activated

Motor Nerve Conductions Vital part of EDX as this important for identifying demyelination and compression Need to do proximal and distal studies to evaluate for conduction velocity, conduction block, temporal dispersion Typical nerves: ulnar, median, peroneal, and tibial. Less common: radial, femoral, phrenic, spinal accessory, facial.

When to order EDX Mononeuropathy Mononeuropathy Multiplex Polyneuropathies Cranial neuropathies (Trigeminal Mononeuropathy (blink reflex) Radiculopathy Myopathy

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