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  1. SNAPs
    • sensory nerve action potentials
    • stim a sensory nerve, get a recording further along that same nerve
  2. 3 rationales for SNAP testing
    • 1) most peripheral neuropathies affect sensory before motor
    • 2) test the distal segment of a sensory nerve axon
    • 3) most sensory neuropathies start distally
  3. amplification needed for SNAPs
    5-20 microvolts (uV) or millionths of a volt

    --- that's more amplification that needed for muscle
  4. latency for SNAPS for median and ulnar nerves
    • median:
    • norm 3.6
    • borderline 3.6-4.0
    • prolonged > 4.0

    • ulnar
    • norm <3.4
    • borderline 3.4-4.0
    • prolonged > 4.0
  5. amplitued for SNAPs for median and ulnar nerves
    • both:
    • norm >15
    • bord 10-15
    • low <10
  6. median and ulnar nerve SNAPS -- to which fingers?
    • med - 1, 2, or 3
    • ulnar - 5
  7. low amplitude in a SNAP means...
    azonal degen and/or partial compression
  8. prolonged latency in a SNAP means...

    (an absent response of course is more severe trouble)
  9. radial nerve testing .. ___dromic?
    always anti never ortho!
  10. UE vs LE, which is affected first in peripheral neuropathies
    usually LE -- bc leg nerves are longer, so there's more surface to be affected
  11. for the LE, conduction velocity below 40 m/sec means
    • all conducting fibers are impaired and are conducting slower than 40 m/sec
    • -- may have demyelination
  12. compression a/o axonal degen of a high percentage of fibers --> what readings?
    decreased CV and decreased amplitude
  13. deep fibular nerve, which muscle?
    extensor digitorum brevis
  14. extensor digitorum brevis attachments
    Proximal dorsal region of middle phalanges 2, 3, 4 --> dorsal lateral calcaneus

    deep fibular nerve
  15. tibial nerve - likely to get compressed where?
    • popliteal fossa
    • tarsal tunnel syndrome
  16. tibial nerve, what muscle?
    abductor hallucis
  17. where do most systemic neuropahties begin?
    distal LEs, so must do LE SNAPs
  18. 3 possible reasons for low amplitude in a SNAP while velocity is normal
    • loss of some axons
    • partial compression
    • demyelination (with associated conduction block)
  19. reason for prolonged latency in a SNAP
    axonal loss
  20. __dromically is SNAP testing done for LEs?
    antidromically (not ortho) always
  21. good early test for neurpathy in a diabetic
    medial planta and dorsal sural nerves -- amplitudes will be reduced prior to standard nerve conduction studies
  22. SSEP's
    somatosensory evoked potentials

    record the conduction of an AP (that started in a sensory nerve) when it reaches the posterior columns of the spinal cord
  23. real basics of how to do a SSEP
    • stim a sensory nerve (UE or LE)
    • record over the sensory cortex, thru the cranium, with subcutaneous EEG needles
    • use a specialized amplifier to average multiple APs
  24. H-reflex
    • the electrical equiv of a myotatic reflex (DTR)
    • records and AP first in sensory fibers going to the SC, then in motor fibers heading to the muscle (so it's all done orthodromically) ... so it looks at conduction along the entire pathway associated with a reflex

    use low intensity stim*
  25. brainstem auditory evoked potentials (BAER) -- what's it for?
    to evaluate auditory pathways to the primary auditory cortex

    I guess it's R rather than P for "response??"
  26. how is a BAER performed?
    headphones produce audible clicks (1 per sec) to produce an AP conducted by the cochlea to the ipsilat temporal lobe ... and I guess it's measured there?
  27. most common etiology of involvement for a BAER
    accoustic neuroma
  28. visually evoked potentials -- tests what?
    visual tracts to the occipital lobe
  29. how is a visually evoked potential test performed?
    use strobe stim (1/sec) to evoke and AP from the retina to the optic radiations to the occipital lobe

    (demyelination may lead to increased latency of initial peak)
  30. how will UMNL impact an H-reflex?
    higher amplitude
  31. how will POLIO impact an H-reflex?
    decreased H reflex bc ant horn cell is shot
  32. how will motor root compression (like from a disc) impact an H-reflex?
    increased latency, decreased amplitude
  33. F wave tests what?
    looks at the backfiring of an ant horn cell, testing its conduction and excitability
  34. the ___dromic stuff in an F wave
    starts antidromically, running up a motor fiber, ends orthodromically running down the motor fiber
  35. how will spasticity influence an F wave?
    increase amplitude
  36. how will spinal shock or motor neuron disease impact an F wave?
    decrease amplitude
  37. M wave
    motor unit AP
  38. SSEP vs F vs H wave, what they test
    • SSEP -- sensory
    • F -- motor, excitability of ant horn cells
    • H -- both
  39. drugs for myesthenia gravis?
  40. prim locations and an early symptom of myesthenia gravis
    extraocular, cervical, shoulder girdle muscles

  41. how to test for myesthenia gravis
    • small needle in intrinsic hand, prox muscles (such as deltoid), and a facial muscle
    • stim repeatedly at various frequencies (5,15, 30, 50)
    • do a very slow sweep speed (up to 30 sec / sweep), looking for decrease in amplitude of motor unit APs (MUAP) 

    healthy should show no decrease in amplitude over 5-10 sec or just a 5% decline, while MG should taper sharper >10%
  42. how should spasticity or increased DTRs impact F wave?
    increased amplitude
  43. flaccidity, polio, Guillian-Barre -- gives what for F-waves?
    • flaccidity - absent
    • polio - absent
    • GB - impaired
  44. ant horn cell problem -- how will it affect F wave?
    • latancy -- normal
    • amplitude -- decreased (bc it reflects the excitability of the horn cell -- if it's a UMNL it'll be high amp)
  45. You did some MG testing and saw a taper. What should you do next to confirm the diagnosis?
    inject a drug that briefly strengthens function at the NMJ and repeat test to see what happens. If the tapering decreases, it looks like it's MG.
Card Set:
2013-10-10 18:47:58

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