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electrodiagnosis, EVOKED POTENTIALS, Strength-Duration curves,…

- - - - A normal response is obtained with ES.
        
        Sometimes the nerve and muscle are hyper-excitable and react to a lower intensity of current than that normally required.
      - LMN
        
        seddon & sunderland classification N inj
        
        table
        
        Neurapraxia
        
        Axonotmesis
        
        Neurotmesis
        
        alternations in the electrical reactions occur.
        
        once the nerve fibres have degenerated,
        alternations in the electrical reactions occur.
        
        ES to the affected muscle - normal response.
        
        But loss of response if stimulus applied to the nerve trunk above the lesion.
        
        Defects of the NMJ
        
        Myasthenia gravis
        
        Muscle lesions
        
        Weakness or disease of the muscle
        
        The reactions to ES are of normal type,
        but are reduced in strength.
        
        Absence of response - ischaemic contracture, advanced stages of the myopathies,
        firbrosis of muscles in long standing denervation.
        
        Functional disorders
        
        Hysterical paralysis
        
        No alternation in the electrical reactions.
        
        Stages of denervation
        
        Wallerian degeneration-14 days to complete
- - - - this is the waveform you see on the screen
        (in order to give more details about what you are describing, more specific terms may
        include compound nerve action potential, compound motor action potential,
        sensory nerve action potential, etc.)
      - Latency
        
        time interval between the onset of a stimulus and the onset of a response
        (can also be referred to as a motor latency or a sensory latency).
        
        Amplitude
        
        the maximal height of the action potential.
        
        Conduction velocity
        
        how fast the fastest part of the impulse travels
        (can also be referred to as a motor conduction velocity or a sensory conduction velocity).
        
        F wave
        
        a compound ms action potential evoked by antidromically stimulating a motor nerve frm a ms using maximal electrical stimulus.
        it represents the time required for a stimulus to travel antidromically toward the spinal cord & return orthodromically to the ms along a very small percentage of fibers.
        
        H-reflex
        
        a compound muscle action potential evoked by
        orthodromically stimulating sensory fibers, synapsing at the spinal level
        and returning orthodromically via motor fibers.
        The response is thought
        to be due to a monosynaptic spinal reflex (Hoffmann reflex) found in
        normal adults in the gastrocnemius-soleus and flexor carpi radialis muscles.
        
        Orthodromic
        
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    - -  Morbid Obesity
         Thin individuals
         Bleeding disorders
         Blood precautions
      - Contraindications
        
         Severe bleeding disorder
         Out of control anticoagulation therapy
         Automatic implanted cardiac defibrillators
         Cardiac pacemaker
         Active skin/soft tissue infection
        
        compllications
        
        infection
        
        bleeding
        
        accidental penetration of the needle into something other than the intended ms
- - - - graph
      - Partial Denervation
        
        graph
        
        kink
  - - - It is quick and easy to perform.
        
        It requires minimal training.
        
        It is economical in comparison to other clinical tests.
      - Disadvantages of the Strength-
        Duration Curve
        
        It only provides qualitative data in relation to the degree of denervation.
        
        it cannot locate the site of the lesion
        
        in large ms, only few fibers can be studied due to the limits of the method.
        
        Rheobase and Chronaxie
        
        Rheobase
        
        is the smallest current that will produce a
        muscle contraction if the stimulus is of infinite duration.
        
        in practice an impule of 100ms is used
        
        in denervation the rheobase may be less than that of innervated ms
        
        Chronaxie
        
        the chronaxie is the duration of the shortest impulse that will produce a response with a current of double the rheobase.
        
        the chronaxie of the innervated ms is appreciably less than that of denervated ms
        
        graph
- - - - surface electrodes
        -ring or disk electrodes,
        -disposable or non-disposable
        
        needle electrodes:
        -monopolar
        -bipolar
        -or concentric
      - EMG
        
        Active (needle electrode)
        
        reference (surface electrode)
        
        ground (surface electrode)
        
        pics
        
        amplifiers
        
        magnify the signal so that it can be displayed
        
        preamplifiers attenuate the biological signal before it gets to the amplifier
        
        filters
        
        are used to reproduce the signal we want while trying ti exclude both high & low frequency electrical noise
        
        display system
        
        vedio or computer screen
  - - - if the needle is properly placed the ms you are testing you will
        hear & see brief electrical activity associated with the needle movement.
        this is called insertional activity
        
        the sound associated with this needle movement has been described as
        ' crisp'
        & it's temporally related to the
        
        high-frequency positive response &
        
        negative spikes
        that are easily visualized on the monitor.
      - normal insertional activity
        
        decreased insertional activity
        
        increased insertional activity
        
        any electrical activity that lasts longer than 300 ms is considered increased
        
        graph
        
        may occur
        when there is ms pathology
        
        & is evidenced by
        
        the presence of positive sharp waves
        
        & sometimes fibrillation potentials that are apparent
        
        only on insertion & do not persist.
        
        occurs when the needle is inserted into an atrophied ms
        
        typically only lasts a few hundred milisecs, just barely longer than the needle movement itself
    - - normal ms
        
        should be electrically silent after needle insertion
      - abnormal
        
        spontaneous activity
        
        spontaneous activity generated by the muscle
        
        Fibrillation potentials (fibs)
        
        PSWs
        
        Myotonic discharges
        
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        positive sharp waves (PSWs) are ms fiber action potentials that can be recorded frm a ms with impaired ms innervation
        or frm an injured potion of a ms.
        
        they tend to fire regularly at a rate of 0.5 to 15 Hz
        
        amplitudes 20-1000microvolts with
        
        durations of 20-30 ms.
        
        PSWs sound like dull thuds.
        
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        are the spontaneous action potentials of single muscle fibers that are firing autonomously.
        
        This can occur in the presence of impaired innervation.
        
        Usually fire in a regular pattern at rates of 0.5–15 Hz,
        
        Usually triphasic in morphology
        
        range from 20 to 1000 microvolts in size.
        
        They sound like raindrops hitting a tin roof.
        
        are of 4 types
        
        fibrilation potentials (fibs)
        
        positive sharp waves (PSW)
        
        myotonic discharges
        
        complex repetitive discharges
        
        spontaneous activity generated by the nerve
        
        Myokymic discharges
        
        Myokymic discharges are groups of spontaneous motor unit
        potentials that have a regular firing pattern and rhythm.
        .
        
        In the continuous form they are seen as single or paired discharges of motor unit potentials that fire
        at rates of 5–10 Hz.
        .
        
        In the discontinuous form they are seen as bursts of motor
        potentials,
        which repeat at 0.1–10 Hz.
        .
        
        sounds like soldiers marching.
        
        Seen in
        
        facial muscles in Bell’s palsy,
        
        multiple sclerosis, and
        
        polyradiculopathy.
        They are also seen in
        
        limb muscles in
        chronic nerve lesions and in radiation plexopathy.
        
        A fasciculation potential
        
        is the potential associated with the
        random and spontaneous activation of a group of muscle fibers
        or all of the muscle fibers originating from a motor unit.
        .
        
        This is generally thought to be due to the abnormal discharge of
        an alpha motor neuron,
        resulting in contraction of all the muscle
        fibers innervated by the motor unit.
        .
        
        They are usually from 0.5 to 3 mv in amplitude and
        -7 to 20 ms duration.
        -The firing pattern is irregular,
        
        has a low frequency of 1 to 2 Hz, and
        .
        
        sounds like a “large raindrops on a tin roof.”
        
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        Endplate Region
        
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        myokymic discharges
        
        cramps
        
        neuromyotonic discharges
        
        tremors
        
        multiples ( multiple motor unit potentials, ie, doublets or triplets
        
        fasciculations (can be considered muscle or nerve generated)
        
        occurs in the presence of pathology
    - - minimally contract the muscle.
        
        Amplitude:
        
        Amplitude of the motor units may be
        
        increased
        
        Increased amplitude
        of motor units
        can be seen with
        
        reinnervation
        
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        decreased
        
        axonal loss
        
        may be seen in myopathies.
        
        normal
        
        Rise Time:
        
        An acceptable rise time is
        
        0.5 milliseconds or less.
        
        Duration:
        
        Normal duration
        
        is about 5–15 milliseconds.
        
        Phases:
        
        Normally, motor unit potentials have
        
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    - - Recruitment refers to the orderly addition of motor units
        so as to
        increase the force of a contraction.
        
        A contraction becomes stronger in 2 ways:
        
        the firing motor units incr their rate of firing
        
        additional motor units commence firing.
        
        normal
        
        Normally the motor unit will fire in a regular pattern at about 5Hz.
        
        At around 10 Hz - another MUAP will be recruited to fire.
        
        abnormal
        
        Neuropathic recruitment, also called neurogenic recruitment
        
        Few motor units fire at an increased rate, or firing frequency.
        .
        
        The firing rates of these MUAPs are greater than 20 Hz (20 cycles per second)
        and may increase to over 30 Hz or more.
        
        can be seen in:
        
        neuropathies,
        
        radiculopathies,
        
        motor neuron disease and
        
        nerve trauma.
        
        Myopathic MUAPs
        
        tend to have an
        
        early recruitment of
        
        short duration low amplitude MUAPs
        
        firing at increased rates.
        
        graph
        
        Polyphasicity and
        
        spontaneous potentials
        can be seen in both neuropathies and myopathies.
- - - - for sensory nerves,
      - compound nerve action potentials (CNAPs)
        
        for mixed
        (sensory & motor)
        nerves
        
        late responses
        
        (primarily F-waves and H-reflexes).
        
        diagrams
        
        Conduction Velocity
        
        is how fast the nerve is propagating an action
        potential. It can be calculated by the formula:
        
        velocity = distance/time
        
        Since motor nerves do conduct across a myoneural junction,
        the conduction velocity cannot be measured directly.
        Therefore, we use the formula:
        
        velocity = change in distance/change in time
        
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        NCS
        
        Active (surface electrode – this is also referred to as the pickup electrode)
        
        Reference (surface electrode)
        
        Ground (surface electrode)
        
        graph
        
        H-reflex
        
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