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Amyloidosis and Neuropathy

  • Probably 1st described in early 18th century-Wainewright described amyloid involving the liver.
  • When stained with Congo red, it produces an apple-green birefringence when viewed under polarized light.
  • Several types of Amyloidosis
    • Primary-no evidence of preceding or coexisting disease except multiple myeloma.
      • Divided into two groups-with/without multiple myeloma.
    • Secondary-coexistence with other conditions such as RA or chronic infection.
    • Localized-involvement of a single organ without evidence of generalized involvement.
    • Familial
    • Senile
    • Endocrine
    • Dialysis arthropathy
  • Cutaneous nerve biopsy is the only certain method to recognize Amyloidosis in a peripheral nerve.
  • Systemic symptoms-weakness, fatigue most frequent occurs 50% of pts. Also ankle edema, hepatomegaly, macroglossia (large tongue), purpura (neck and face, upper eyelids)
  • Carpal tunnel syndrome or peripheral neuropathy found in 1/6 of with primary Amyloidosis, usually present at least one year prior to dx. Peripheral neuropathy involves sensory more than motor, lower extremity more than upper extremity, distal more than proximal. Dysautonomia often severe due to small non-myelinated pathology.
  • Prognosis:  mean duration of pts with primary type within one month of dx at Mayo-13 months. Only 7% survived more than 5 yrs.

CIDP

CIDP
·       Chronic Inflammatory Demyelinating Polyradiculoneuropathy-acquired PN of presumed autoimmune basis; chronically progressive or relapsing/remitting forms.·

  • Sx develop sub-acutely or insidiously over weeks to months.
  • Contrasts with AIDP that develops acutely over few days or weeks.·
  • Responds to immune modulating treatment. Responds to steroid, IVIg. Plasma exchange, other immunosuppressive meds may be also used.·
  • Early signs/sx:  paresthesia; painful sx such as burning/searing jabbing pain less common.  Tremors, limb/gait ataxia, loss of balance may reflect impaired proprioception. Significant disability may occur.
  • ·       Link with pre-ceding viral or bacterial infection less apparent than AIDP.
  • ·       Macrophage induced segmental demyelination usually accompanied by nerve edema and infiltrates of mononuclear inflammatory cells.

·       Pathology

  • ·       Symmetric neuropathy with proximal nerves (even CNS) involved.
  • ·       Paranodal, internodal segmental demyelination.  ?macrophage induced
  • ·       Perivascular lymphocytes frequently seen in epineurium
  • ·       Some axonal degeneration.
  • ·       Edema, epineural and endoneural inflammation.
  • ·       Onion bulb formation, scarring.
  • ·       No strong evidence for characteristic antibody.
  • ·       Anatomic-motor greater than sensory; large greater than small fiber; proximal (root/plexus/proximal nerves) more than distal nerves.

·       Diagnostic criteria

  • ·       Symmetric proximal/distal weakness.
  • ·       Sensation especially proprioception impaired; numbness/tingling/parasthesia.
  • ·       Generalized motor/sensory neuropathy; multifocal inflammatory demyelination.
  • ·       Cranial nerves may be affected.
  • ·       Disease progression for longer than 8 weeks or relapsing course mandatory for dx.

·       Lab findings

  • ·       Protein content in CSF elevated; lymphocyte count less than 10/mm.
  • ·       Inflammatory demyelination with nerve biopsy; maybe some axonal loss.
  • ·       Trial of therapy may aid dx.

·       EMG/NCS

  • ·       Slow motor/sensory NCV
  • ·       Sensory SNAP responses may be absent.
  • ·       Strong emphasis on focal conduction block/increased temporal dispersion in several motor nerve segments.
  • ·       Little/no positive sharp wave, fibrillation activity.

 

Multifocal Motor and Sensory Demyelinating Neuropathy

   CIDP varient-affects upper limbs in asymmetric fashion.

·       Different designations

  • ·       Multifocal motor and sensory demyelinating mononeuropathy (MDSMM)
  • ·       Upper limb-predominate multifocal chronic inflammatory neuropathy.
  • ·       Multifocal acquired demyelinating motor and sensory neuropathy (MADSAM)

 

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All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

Critical Illness Polyneuropathy

Critical Illness Polyneuropathy
The neuromuscular syndrome of acute limb and respiratory weakness that commonly accompanies patients with multi-organ failure and sepsis constitutes critical illness polyneuropathy. It is a major cause of difficulty in weaning off the patient from the ventilator after respiratory and cardiac causes have been excluded.

It is usually an axonal motor-sensory polyneuropathy, and is usually associated with or accompanied with a coma producing septic encephalopathy. The neuropathy is usually not apparent until the patient’s encephalopathy has peaked, and may be noted only when the brain dysfunction is resolving. Patients usually have a protracted hospital course complicated by multi-organ failure and the systemic inflammatory response syndrome. Elevated serum glucose levels and reduced albumin are risk factors for nerve dysfunction, as is prolonged intensive care unit stay.

Polyneuropathy may develop after only one week of the systemic inflammatory response syndrome, but the frequency tends to correlate with the duration of the severe illness.

Electrophysiologic findings are those of a pure axonal degeneration, affecting motor greater than sensory fibers. Conduction velocities and distal latencies are relatively intact, but there is a reduction in the compound muscle and the sensory nerve action potentials. Needle EMG reveals fibrillation potentials and positive sharp waves indicating active denervation. Even in the more advanced stages of critical illness polyneuropathy, conduction velocities and distal latencies remain relatively normal, emphasizing the purely axonal nature of the neuropathy. In the acute setting, if sensory response is normal, a diagnosis of critical illness “motor” polyneuropathy should not be made without excluding myopathy.

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Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

Diabetic Neuropathy

Diabetic Neuropathy
PathophysiologyThe factors leading to the development of peripheral neuropathy in diabetes are not understood completely, and multiple hypotheses have been advanced. It is generally accepted to be a multifactorial process. Important contributing biochemical mechanisms in the development of the more common symmetrical forms of diabetic polyneuropathy likely include the following:Polyol pathway

• Hyperglycemia causes increased levels of intracellular glucose in nerves

• Leads to saturation of the normal glycolytic pathway.

• Extra glucose is shunted into the polyol pathway

• Converted to sorbitol (sugar alcohol) and fructose by the enzymes aldose reductase and sorbitol dehydrogenase.

• Accumulation of sorbitol and fructose

• Lead to reduced nerve myo-inositol, (An isomer of glucose that has traditionally been considered to be a B vitamin although it has an uncertain status as a vitamin and a deficiency syndrome has not been identified in man. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1379) Inositol phospholipids are important in signal transduction.)

• Leads to decreased membrane Na+/K+ -ATPase activity, impaired axonal transport, and structural breakdown of nerves, causing abnormal action potential propagation.

• This is the rationale for the use of aldose reductase inhibitors to improve nerve conduction.4

While most cells require the action of insulin for glucose to gain entry into the cell, the cells of the retina, kidney, and nervous tissues are insulin-independent, so glucose moves freely across the cell membrane, regardless of the action of insulin. The cells will use glucose for energy as normal, and any glucose not used for energy will enter the polyol pathway.

Advanced glycation end products (AGE)

The nonenzymatic reaction of excess glucose with proteins, nucleotides, and lipids results in advance glycation end products that may have a role in disrupting neuronal integrity and repair mechanisms through interference with nerve cell metabolism and axonal transport.5

Oxidative stress

The increased production of free radicals in diabetes may be detrimental via several mechanisms that are not fully understood. These include direct damage to blood vessels leading to nerve ischemia and facilitation of AGE reactions. Despite the incomplete understanding of these processes, use of the antioxidant alpha lipoic acid may hold promise for improving neuropathic symptoms.

Main Pathologic features of diabetic neuropathy.

• Loss of myelinated and unmyelinated fibers.

• Myelinated nerve fiber loss may be diffuse or patchy.

• Clusters of regenerating fibers may be abundant.

• Thickening of endoneurial blood vessels.

• Increased durability and rigidity of Schwann cell basal laminae.

 

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All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

EMG exam

The EMG exam

With an intramuscular electrode, recordings are made with the muscle at rest and working to view for evidence of neurogenic or myogenic pathology. Waveforms are observed on the oscilloscope, mediated through the EMG needle electrode and amplifier.
Insertional activity

Normal muscle will have a significant characteristic with EMG exam. Brief insertional activity will be observed on the oscilloscope when the needle is moved through the sarcolemma, referred to as injury potentials. Muscle that is fibrotic and severely atrophied from myopathy or long standing denervation will have reduced insertional activity.
Spontaneous abnormalities

A normal muscle at rest will have a characteristic silent baseline. Spontaneous abnormalities may be seen in a muscle suffering from acute denervation. Fibrillation and positive sharp waves are commonly seen after nerve injury, the origin of such is postulated to be due to a metabolic change within the muscle after denervation, or the result of increased post synaptic receptor sensitivity to acetylcholine after denervation. The fact that curare does not inhibit fibrillation in the wake of denervation argues against the latter theory. Fibrillation and positive sharp waves are the result of spontaneous discharge of a single muscle fiber.
Other forms of spontaneous abnormalities include complex repetitive discharges and fasciculation potentials. Complex repetitive discharges are the result of several muscle fibers spontaneously firing through ephaptic transmission, with one fiber serving as a pacemaker. Fasciculation potentials are the result of the spontaneous discharge of a motor unit, are commonly benign in origin, but may be seen with other EMG abnormalities in diseases such as ALS.

fibs
fibrillation, positive sharp wave activity at rest

Volitional EMG Exam

After observing the muscle at rest, EMG activity accompanying volitional effort is observed. Electrical activity accompanying motor unit discharge will be recorded with the EMG needle, amplified and viewed on the oscilloscope screen. The amplitude and configuration of the motor units is observed, as well at the recruitment order and motor unit firing frequency.
Normal motor unit recruitment will be orderly and graded, according to Henneman’s size principle. With minimal effort, small motor units are recruited, firing at a particular frequency. With increased effort, these motor units will increase firing rate, with larger motor units recruited with more demand on the muscle. Innervated motor unit discharge will be synchronous across the X-axis, and be biphasic, triphasic, or quadriphasic in shape. The amplitude of the normal motor unit observed on the oscilloscope usually is less than 5 mV, with small amplitude motor units recruited first, larger motor units usually recruited with more forceful effort.
In neurogenic pathology, the number of motor units that are available for muscle force is compromised. The remaining motor units tend to fire more rapidly in order to comply with demand on the muscle for more force. This is referred to as late, decreased, or neurogenic recruitment. There is decreased number of motor units recruited per contraction force compared to normal. The shape of the motor unit after re-innervation will tend to be polyphasic, as its discharge will no longer be synchronous, due to collateral sprouting. A motor unit with five or more phases is referred to as polyphasic. Small amplitude polyphasic motor units are observed with early or immature re-innervation. With chronic re-innervation, the amplitude of the motor unit will increase, as will its duration, owing to the greater size of the new motor unit. A motor unit greater than 5 mV is referred to as a giant motor unit, and consistent with longer standing re-innervation.
polyphasic
polyphasic motor unit potential
In myogenic pathology, the number of motor units available for discharge is not compromised. However, the contractile strength of each motor unit is reduced due to sick muscle fibers. With little demand upon the muscle, a greater number of motor units needs to be recruited in order supply the necessary force. This is referred to as early, increased, or myogenic recruitment. The amplitude of the motor units will be decreased, and may appear polyphasic. Some of the polyphasia observed may simply be several individual motor units abutting in time.
Incomplete motor unit activation will be observed when a patient’s effort is reduced because of pain, fear, hysteria, or malingering. In this instance, the recruitment pattern observed will be normal in number per contraction force, with normal amplitude, shape, and firing frequency.

 

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All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

EMG Spontaneous Abnormalities

EMG Spontaneous Abnormalities

EMG spontaneous abnormalities

Fibrillation
Positive sharp waves
Fasciculation potentials
Complex repetitive discharges
Myokymic potentials
Myotonia
Fibrillation

Originate from spontaneous firing of single muscle fiber
Detectable 2-3 weeks after “denervation”
Initial positive deflection, negative spike
consistent with axonal degeneration
may be seen in acute myopathy
sound like rain on tin roof or fat frying in a pan
Positive sharp waves

Originate from spontaneous firing of single muscle fiber
May appear earlier than fibs
Initial positive deflection without negative spike
Sound like ticking of clock
Fasciculation potential

Spontaneous discharge of all or part of a motor unit
Muscle fasciculation visible clinically as “twitching” or worm like movements
Appear similar to volitional MUP; must make sure muscle at rest
May be benign or pathologic
Complex Repetitive discharges

Result of ephaptic activation of neighboring muscle fibers
One muscle fiber acts as generator
Non specific abnormality; hyper-irritable muscle membrane
Sound like motor boat or motor cycle
Abruptly start or stop
Myokymic Potentials

Represent rhythmic firing of “grouped” MUPs
“grouped fasciculations”
sound like footsteps of marching soldiers
always pathologic
common in radiation induced brachial plexopathy
Myotonic discharge

“dive bomber” sound
waxing and waning of amplitude, frequency
induced by tapping muscle or moving needle
represent “delayed relaxation” of muscle fibers
seen in Myotonic dystrophy, myotonia congenita

 

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Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

E-Stim

E Stim

 Direct CurrentThe simplest source of energy for direct current is a battery, where chemical reactions produce an excess of electrons at the one pole (cathode), and a deficiency of electrons at the other pole (anode).  When connected through a closed circuit, electrons flow from an area of high concentration (cathode), to an area of low concentration (anode).sea waterAlthough the movement of particles is from negative to positive poles, by convention, current (I), is defined by moving from positive to negative terminals. 

Voltage or EMF (electron moving force) may be thought of as the storage of energy behind a dam. This amount of stored energy is analogous to potential difference.

 

Current flow occurs only when a circuit is closed (or the dam is opened).  Current will flow from area of excess to deficiency until the source is exhausted, or difference is eliminated. The strength of the current flow is measured in amperes, or milliamperes.

 

current flow

 

Historically described as galvanic current, unidirectional flow of charged particles is referred to as direct current, or monophasic.  Flow of current may be continuous or interrupted. Interrupting the current into pulses (making and braking the circuit) will have the affect of depolarization of nerve or muscle.  Continuous DC ( un-interrupted) current has applications in iontophoresis and wound healing.

 

Current waveform plotted in graph form by convention is represented by the X-axis as a function of time, and Y-axis as a function of current magnitude.

 

image005

Interrupted DC current.  Four monophasic pulses of undefined current strength or duration.

image007

Each “twin peak” represents one mono-phasic pulse of undefined current amplitude. The pulse duration measures 100 usec.; phase duration undefined.

high voltage

 

The duration of the phase along the X-axis is referred to as the phase duration.

Phase duration can be affected by the waveform configuration. In the first instance, the pulse and phase duration is equal; in the second the phase duration is shorter than the pulse duration, due to its configuration.

 image011

 

 

 

Alternating Current

Alternating current is defined as bi-directional flow of charged particles.  To produce this type of current, the voltage applied across the circuit is periodically reversed, allowing electrons to flow in one direction, and then the other.  The result is a biphasic pulsed current.  Each pulse contains a phase below and above the X-axis.

 

Each pulse may be further defined by whether or not opposing phase configurations is symmetric or asymmetric.

 

Top drawing-4 biphasic pulses; bottom drawing-2 biphasic pulses.

image013

 

The duration of the phase above the x-axis is added to the duration of the phase below the x-axis to determine the pulse duration.  Interpulse and interphase intervals are self-explanatory.

 

image015

 

Polar affects and phase charge

The area under the curve of each phase is a function of the phase charge, expressed in coulombs.  The greater the area, the greater the amount of phase charge.  The amount of charge is applicable to how much energy is being introduced physiologically, and if any polar affects will occur.

 

image017

Faradic Current

Historically, a waveform referred to as faradic was introduced subsequent to simple make and brake galvanic (monophasic pulsed) current.  It was more comfortable than pulsed DC, as its duration was usually shorter.  It also had less polar effects due to its waveform.

 

Faradic current-assymetric biphasic pulse.

 

image019

Russian Current

Developed as a tool for Russian athletes, it was thought that a high frequency pulse had the effect of lowering resistance and therefore allowing for more efficient delivery of current.

 

Continuous sine wave (polyphasic) waveform with a carrier frequency of 2500 Hz, modulated to yield 50 pulses.

russian

 

“High Volt” Stimulation

Monophasic pulsed current with very short phase duration (5-20 usec) and very high peak current amplitude (2000 to 2500 mA).  This waveform may prove beneficial for treating edema.

  

High voltage monophasic pulsed “twin peak” current

 

image023

Regulation and Modulation of Electrical Stimulation

 

·       Waveform selection controls

Many devices allow the selection of a particular type of waveform (russian, faradic, etc).  Others will provide only one type of current waveform.  It is important to review operation manuals to identify what type of current waveform that is available.

 

·       Amplitude controls

Output is regulated in volts, amps, or both.  Some sort of measurement scale is usually observed, but may have no direct relationship to the amount of current or voltage being applied.

 

·       Balance controls

When more than two electrodes are available, this will allow more stimulation to be directed to one particular electrode set.

 

·       Frequency controls

Permit the variation of number of pulses per second.  This may be labeled rate, burst rate, or frequency.  Some machines (russian) may have frequency established automatically.

 

·       Duty cycle

Allows a cycle stimulation followed by a rest period during the treatment time established.

 

·       Ramp time

Permit modulation of amplitude, frequency, or duration of the current gradually.  Usually, ramping the amplitude is utilized to allow for gradual onset of a strong muscle contraction.  Some machines also allow for “ramp off” allowing for gradual relaxation of muscle contraction.  This may also be labeled surge time, or slope time.  Some machines will automatically ramp certain waveform characteristics.

 

·       Constant or continuous mode

Allow for “continuous” trains of stimulation at waveforms established automatically or manually, without a duty cycle.  This will allow the clinician the ability to establish a certain level of stimulation and desired muscle contraction prior to choosing a particular duty cycle.

 

·       Alternate or reciprocal mode

Permits the use of more than one set of electrodes; cycling stimulation between the sets of electrodes.

 

·       Treatment timer

Self-explanatory.  Allows clinician to set time of stimulation session.

 

·       Wimp  switch

Some machines permit a on/off switch to be utilized by the patient through a cord to the machine, in the event the patient needs to turn the current off.

 

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All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com

Excitation Contraction Coupling

Excitation Contraction Coupling

muscle
Muscle fiber anatomy/structure
• Epimysium; connective tissue covering the muscle.• Muscle fibers are grouped into fascicles, covered by perimysium.• Endomysium; connective tissue covering each individual muscle fiber.• Sarcolemma; thin surface membrane of the muscle fiber.• Sarcoplasm ; semi-fluid plasm and intracellular content of the muscle fiber.• Myosin and Actin are myo-fibrils, arranged in parallel within the sarcoplasm, responsible for muscle fiber contraction.

• Myosin molecules are thick filaments.

• Thin filaments made of actin molecules bound to troponin and tropomyosin.

• A sarcomere is a sub-unit within the muscle fiber, capable of contraction. It consists of strands of actin and myosin arranged in parallel.

• Transverse tubule (T-tubule). Transverse orientation with relation to muscle fiber; structurally internal to the muscle fiber cell, but contains extracellular fluid. Muscle action potentials travel through T tubules to into the muscle.

• Longitudinal tubule ( Sarcoplamic reticulum); expand to form bulbous Terminale Cisternae at the junction with T-tubules. Longitudinal tubules do not contain sarcoplasm or extra-cellular fluid. Two Terminale Cisternaes and one interposed T-Tubule form a triad in longitudinal sections of muscle.

muscle1
Excitation-contraction coupling refers to the link between the electrical impulse nerve event and the mechanical component of muscle fiber twitch.
• Nerve impulse at the motor end plate spreads over the outer surface of the muscle fiber, through the T-tubules, coming into contact with Terminal Cisternae and then the Longitudinal tubules. • Ca++ is released from the Longitudinal tubules (Sarcoplasmic Reticulum) into the sarcoplasm.
muscle2
• Ca++ binds to troponin within the sarcoplasm, resulting in bridge formation between actin and myosin filaments.• Cross bridge formation causes actin fibers to slide relative to the thicker myosin strand.• Calcium is sequestering into the sarcoplasmic reticulum (in the presence of adenosine-triphosphate) breaking the existing bridge, relaxing the contraction.
muscle3

 

Contents of this web site © Ray Jurewicz
All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com Web Site design by Larry Berman and Chris Maher

Friedrich’s Ataxia

Friedrich’s Ataxia     Spinocerebellar Degeneration
·       Autosomal recessive; present symptoms late childhood/early adult.·       Ataxic gait, loss of dexterity.·       Pathology-posterior root fibers, sensory fibers of peripheral nerve degenerate. Dorsal root ganglion cell loss.  Central loss also in posterior/lateral columns of spinal cord.

·       Corticospinal fiber loss leads to weakness of the legs, extensor plantar responses.

Evoked sensory SNAP responses small or absent.  Normal motor NCS

Contents of this web site © Ray Jurewicz
All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com Web Site design by Larry Berman and Chris Maher

Glossary of EPS terms

Glossary

Action potential-The all or none, self -propogating, non-decrementing voltage change recorded from an excitable cell.
Amplitude-The maximal voltage difference between two points, usually measured baseline to peak
Anode-The positive terminal of a source of electrical current.
Antidromic-Said of an action potential or of its stimulation causing the action potential that propogates opposite to the normal (dromic or Orthodromic) one for that fiber—i.e., conduction along motor fibers toward the spinal cord and conduction along sensory fibers away from the spinal cord. Contrast with Orthodromic.
Artifact-A voltage change generated by a biological or nonbiological source other than the ones of interest. The stimulus artifact is the potential recorded at the time the stimulus is applied and includes the Electrical or shock artifact, which is potential due to the volume conducted electrical stimulus. The stimulus and shock artifacts usually precede the activity of interest. A Movement artifact refers to a change in the recorded activity due to movement of the recording electrode.
Axonotmesis- Nerve injury characterized by disruption of the axon and myelin sheath but with preservation of the supporting tissues, resulting in axonal degeneration distalk to the injury site.
Baseline-The potential difference recorded form the biological system of interest while the system is at rest.
Bipolar needle electrode-A recording electrode with two insulated wires side by side in a metal cannula whose bare tips act as the active and reference electrodes. The metal cannula may be grounded.
Cathode-The negative terminal of a source of electrical current.
Chronaxie- See Strength-Duration curve.
Complex repetitive discharge-Polyphasic or serrated action potentials that may begin spontaneously or after needle movement. They have uniform frequency, shape, and amplitude, with abrupt onset, cessation, or change in configuration. Amplitudes range form 100 uV to 1 mV and frequency of discharge from 5-100 Hz.
Compound Muscle Action Potential (CMAP)-The summation of nearly synchronous muscle fiber action potentials recorded from a muscle commonly produced by stimulation of the nerve supplying the muscle.
Compound Sensory Nerve Action Potential- The action potential recorded by stimulation of mixed nerve with sensory stimulation, or by stimulating sensory fibers and recording from mixed nerve, or stimulating and recording from sensory fibers.
Concentric needle- Recording electrode that measures potential difference between the bare tip of the central wire (active electrode) is flush with the bevel of the cannula (reference electrode).
Conduction block- Failure of an action potential to be conducted past a particular point in the nervous system.
Conduction Velocity-Speed of propagation of an action potential along a muscle or nerve.
End plate activity- Spontaneous electrical activity recorded with a needle near or in the muscle end plate; packets of acetylcholine are mechanically disrupted by the needle.
End plate noise- Graded, non- propogating potential recordings resulting from mechanical disruption of packets of acetylcholine.
Fasciculation- The random, spontanous twitching of a group of muscle fibers which may be visable from the skin.
Fasciculation potential- The electrical potential associated fasciculation which has the dimensions of a motor unit potential that occurs spontaneously as a single discharge.
Fibrillation- The spontanous discharge of individual muscle fiber which are not ordinarily seen through the skin.
Fibrillation potential- The electrical activity associated with fibrillating muscle fibers, reflecting the action potential of a single muscle fiber, occurring spontaneously. Fibrillation is commonly seen with axonal denervation, but is also reported in myogenic pathology, in particular inflammatory muscle disease.
F wave- A late compound action potential evoked from a muscle with supramaximal electrical stimulation to the nerve. Compared with the M wave of the same muscle, the F wave has a reduced amplitude and variable configuration and a longer, more variable latency. The F wave is due to the antidromic activation of motor neurons.
Ground electrode- An electrode connected to a large conducting body (such as earth), use as a common return for electrical circuit and as an arbitrary zero potential reference point.
H reflex (H wave)- A late compound muscle action potential having a consistent latency evoked regularly, when present, form a muscle by an electrical stimulus to the nerve. The H wave is recorded by stimulation of the sensory Ia fibers, which synapse and cause orthodromic activation of the alpha motor neuron. With supramaximal stimulation, the H wave is inhibited.
Insertional activity- Electrical activity caused by insertion or movement of a needle electrode.
Interference pattern- Electrical activity recorded from a muscle with a needle electrode with voluntary contraction.
Late response- A general term used to describe an evoked potential having a longer latency than the M wave. See H or F wave.
Latency- Interval between the onset of a stimulus and the onset of the evoked response.
Membrane instability- Tendency of a cell membrane to depolarize spontaneously or after mechanical irritation or voluntary activation.
Miniature end plate potential- when recording with microelectrodes, discharges recorded at the myoneural junction; thought to be due to small quanta of acetylcholine released spontaneously.
Monopolar needle electrode- A solid wire, usually of stainless steel, coated, except at its tip, with insulating material; usually used as a recording cathode, used with a reference anode electrode place on the skin.
Motor Unit- The anatomic unit of an anterior horn cell, its axon, the neuromuscular junction, and all the muscle fibers innervated by the axon.
Motor unit action potential (abbr. MUAP)- Action potential reflecting the electrical activity of a single anatomic motor unit. It is the compound action potential of those muscle fibers within the recording range of an electrode.
Motor unit territory- The area in a muscle over which the muscle fibers belonging to an individual motor unit are distributed.
Myotonia- The clinical observation of delayed relaxation of muscle after voluntary contraction or percussion. The delayed relaxation may be electrically silent or accompanied by propagated electrical activity such as myotonic discharge.
Myotonic discharge- Repetitive discharges at rates of 20-80 Hz; Potential forms are recorded after voluntary muscle contraction, or after muscle percussion, and are due to independent, repetitive discharges of single muscle fibers. The amplitude and frequency of the potentials must both wax and wane to be identified as myotonic discharges. This change produces a characteristic music sound in the audio display of the EMG due to corresponding change in pitch, which has been likened to the sound of a “dive bomber”
Neuropraxia- Failure of nerve conduction, usually reversible, due to metabolic or microstructural abnormalities without disruption of the axon.
Neurotmesis- Partial or complete severance of a nerve, with disruption of the axons, myelin sheaths, and the supporting connective tissue, resulting in degeneration of the axons distal to the injury site.
Orthodromic- Propagation of an impulse in the direction the same as physiologic conduction; e.g., conduction along motor nerve fibers towards the muscle and conduction along sensory nerve fibers toward the spinal cord.
Phase- That portion of a wave between the departure from, and the return to, the baseline.
Polyphasic potential- an action potential with five or more phases. Seen with EMG exam, usually consistent with re-innervation. Reportedly seen also with denervation, and on with volitional exam of myogenic disorders.
Postive sharp wave- A biphasic, positive-negative actin potential initiated by needle movement and recurring in uniform, regular pattern at a rate of 1-50 Hz. The initial positive deflection is rapid (sharp), followed by a longer duration, smaller amplitude positive deflection. Positive sharp waves are seen in areas of fibrillating muscle fibers, and may represent fibrillation. Commonly seen in axonal injury and inflammatory muscle disease.
Recruitment- The successive activation of the same and additional motor units with increasing strength of voluntary muscle contraction.
Reference electrode- The anode electrode, used in conjunction with a cathode recording (active) electrode. Both anode and cathode allow for measuring potential difference.
Rheobase- See Strength-Duration curve.
Spontaneous activity- Electrical activity recorded from muscle or nerve at rest after insertion activity has subsided and when there is no voluntary contraction or external stimulus.
Stimulus- Any external agent, state, or change that is capable of influencing the activity of a cell, tissue, or organism. In clinical NCS, an electrical stimulus is generally applied to a nerve or a muscle. The electrical stimulus may be described in absolute terms or with respect to the evoked potential of the nerve or muscle. In absolute terms, its waveform, duration, and amplitude define the electrical stimulus. A stimulus that evokes the maximum response is considered a maximal stimulus, with 20% additional voltage not producing increased amplitude of the evoked response labeled a supra maximal stimulus.
Strength-Duration curve- Graphic presentation of the relationship between the intensity (Y axis), and various durations (X axis) of the threshold stimulus for a muscle with the stimulating cathode positioned over the motor point. The rheobase is the intensity of an electrical current of infinite duration (300 ms in clinical practice) necessary to produce a minimal visible twitch of a muscle when applied over a motor point. The chronaxie is the duration of the pulse at twice the rheobase to elicit the first visible muscle twitch.
Temporal Dispersion- Relative dysychronization of components of a CMAP due to different rates of conduction of the synchronously evoked component from the stimulation point to the recording electrode.
Volitional activity- Examining a muscle with an EMG electrode during voluntary contraction.
Volume Conduction- Spread of current from a potential source through a conducting medium, such as the body tissues.

Contents of this web site © Ray Jurewicz
All text and images are protected under United States and International copyright laws.

Ray Jurewicz
412-731-0173
E-mail: rj@NerveStudy.com Web Site design by Larry Berman and Chris Maher