Demystifying Electrodiagnostic Studies

Demystifying Electrodiagnostic Studies RICHARD RADECKI M.D. Spine Orthopedic & Rehabilitation Center 700 Lomas Three Woodward Center Albuquerque, NM 87102 505.242.1711 Common reasons for NCS/EMG • Symptoms – Numbness/tingling – Extremity or radicular pain – weakness • Physical findings – Reflex loss or asymmetry – Weakness – Sensory loss • Touch • Temperature • proprioceptive Terms in NCS/EMG studies • Nerve conduction studies • Electromyographic studies • Motor nerve conduction studies • Sensory nerve conduction studies • • • • • • • Latency Amplitude Duration Area Conduction velocity F-wave H-reflex Terms in NCS/EMG studies Insertional activity • Fibrillation potentials – Positive sharp waves • Fasciculation potentials • Complex repetitive discharges • Myotonic discharges • Myokymic discharges Voluntary activity MUAP (Motor Unit Action Potentials) • Amplitude • Duration • Recruitment Nerve Conduction Studies • Studies of the waveforms generated in the peripheral nervous system. – Motor nerve conduction • Stimulation of a peripheral nerve while recording from a muscle innervated by that nerve. – Sensory nerve conduction • Stimulation a mixed nerve while recording from a mixed or cutaneous nerve Electromyography • Electric picture of the muscle. • The electric activity recorded by a needle electrode in muscle fibers during firing singly or in groups near the electrode. NCS: Latency • Interval between the onset of a stimulus and the onset of a response. NCS: Amplitude • The maximum voltage difference between two points • 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. NCS: Duration • The time from onset to termination. • Total duration measures the dispersion of all components. • Measures the differences in conduction of the nerve fibers. NCS: Area • The space under the curve of the waveform. • Area provides the most direct estimate of the amount of functioning nerve tissue that is generating the waveform. NCS: Conduction Velocity • 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. NCS: F-wave • Represents the activation of a motor nerve with subsequent conduction toward the spinal cord and return of conduction back “down” the nerve. • Used to assess the more proximal segments of a peripheral motor nerve. NCS: H-reflex • Due to a spinal reflex. • Represents the activation of a sensory nerve with subsequent conduction toward the spinal cord and return of conduction back “down” the motor nerve. • Used to assess conduction along the proximal segment of sensory fibers and the entire length of the motor fibers. EMG Analysis • Insertional activity • Spontaneous activity – Abnormal electrical patterns • Voluntary activity – Appearance of the motor unit (nerve and muscle unit) action potential Insertional activity • Electrical activity caused by insertion or movement of a needle electrode. • The amount of activity may be described as normal, increased or reduced. – Increased (Denervated muscle, myopathies) – Reduced (Replacement by fat or connective tissue) Spontaneous Activity • Fibrillation potentials • Positive sharp waves • Fasciculation potentials • Myotonic discharges • Complex repetitive discharges • Myokymic discharges • Cramps • Neuromyotonic discharges Fibrillation Potentials • “Ticking clock” • Any muscle fiber that is not innervated can be expected to fibrillate. • Therefore, both diseases involving the nerve, neuromuscular junction and the muscle show fibrillation potentials. • Positive sharp waves. Fibrillation Potentials • Lower motor neuron diseases: – Radiculopathies – Peripheral neuropathies – Mononeuropathies – Plexopathies – Anterior horn cell diseases Fibrillation Potentials • Neuromuscular junction diseases: – Myasthenia gravis – Botulinum intoxication • Muscle diseases: – Myositis – Duchenne and Myotonic dystrophy – Rhabdomyolysis – Muscle trauma Fasciculation potentials • “Raindrops on a roof” • These are most common in chronic nerve disorders: – Nerve root compression – Amyotrophic lateral sclerosis – Peripheral neuropathy – Tetany – Thyrotoxicosis Complex Repetitive Discharge • “Motor boat” • CRD’s are seen commonly in chronic diseases of the nerve and muscle. – Neuropathies: chronic radiculopathies and neuropathies, polio, ALS, and spinal muscular atrophy. – Myopathies: Polymyositis, Duchenne dystrophy, etc. Myotonic Discharge • “Dive bomber” • These are seen in diseases of the muscle. – Polymyositis – Myotonic dystrophy Myokymic Discharges • “Marching soldiers” • May be seen in the following disorders: – Extremity • Chronic nerve compression (e.g. Carpal tunnel) • Radiation plexopathy – Facial • Polyradiculopathy • Multiple sclerosis MUAP • Motor Unit Action Potential • Electric activity of a single motor unit. – A motor unit consists of the anterior horn cell, its axon, the neuromuscular junctions, and all of the muscle fibers innervated by the axon. Motor Unit Action Potential Amplitude Motor Unit Action Potential Duration EMG: Recruitment • When a muscle is voluntarily contracted a single motor unit may fire. • As the muscle is further contracted more motor units are added or recruited. • Normally, recruitment of additional motor units occurs at relatively low levels of effort. EMG: Recruitment • If there is a loss of MUPs with any disease process the recruitment is reduced. – Loss of nerve – Conduction block at the neuromuscular junction – Sufficient loss of muscle fibers EMG: Recruitment • If more motor units are activated than would be expected for the muscle force exerted this is called rapid recruitment. – myopathies Motor Nerve Study Left Median Nerve Rec Site: APB STIM SITE Wrist Elbow Left Ulnar Nerve Rec Site: ADM STIM SITE Wrist B.Elbow A.Elbow Lat (ms) Norm Lat Dur (ms) Amp (mV) Area (mVms) Dist (mm) C.V. (m/s) 4.7 8.9 <4.2 5.9 6.3 4.2 3.5 15.8 13.3 80 210 49.4 Lat (ms) 3.5 6.4 9.7 Norm Lat <3.7 Dur (ms) 5.6 6.2 6.5 Amp (mV) 6.7 7.0 6.1 Area (mVms) 17.0 18.3 17.6 Dist (mm) 80 190 150 C.V. (m/s) 65.1 46.2 Sensory Nerve Study Left Median Nerve Rec Site: Wrist STIM SITE Thumb Left Ulnar Nerve Rec Site: Wrist STIM SITE Lat (ms) 4.3 Norm Lat <3.5 Dur (ms) 0.1 Amp (uV) 11.9 Dist (mm) 140 C.V. (m/s) 32.4 Lat (ms) Norm Lat Dur (ms) Amp (uV) Dist (mm) C.V. (m/s) 5th dig 3.2 <3.5 0.9 15.3 140 43.3 Patient: Sex: Age: I.D.#: Jane Doe Female 58 2797 Test Date: 02/27/03 History/Comments: Left upper extremity pain and parethesias. Motor Nerve Study Left Median Nerve Rec Site: APB STIM SITE Wrist Elbow Left Ulnar Nerve Rec Site: ADM STIM SITE Wrist B.Elbow A.Elbow Lat (ms) 4.7 8.9 Norm Lat <4.2 Dur (ms) 5.9 6.3 Amp (mV) 4.2 3.5 Area (mVms) 15.8 13.3 Dist (mm) 80 210 C.V. (m/s) 49.4 Lat (ms) 3.5 6.4 9.7 Norm Lat <3.7 Dur (ms) 5.6 6.2 6.5 Amp (mV) 6.7 7.0 6.1 Area (mVms) 17.0 18.3 17.6 Dist (mm) 80 190 150 C.V. (m/s) 65.1 46.2 Sensory Nerve Study Left Median Nerve Rec Site: Wrist STIM SITE Thumb Lat (ms) 4.3 Norm Lat <3.5 Dur (ms) 0.1 Amp (uV) 11.9 Dist (mm) 140 C.V. (m/s) 32.4 Left Ulnar Nerve Rec Site: Wrist STIM SITE Lat (ms) Norm Lat Dur (ms) Amp (uV) Dist (mm) C.V. (m/s) 5th dig 3.2 <3.5 0.9 15.3 140 43.3 Questions Thank You!