Chapter 27 Neurodiagnostics Flashcards

Question

What causes fibs and sharps on EMG?

Answer 1

Spontaneously firing, hypersensitive, single myofibres as result fo destabilization of sarcolemma membrane Secondary to denervating disease or primary myopathic change

Answer 2

Spontaneous discharge of single myofibre *plus* its surrounding myofibres. Usually seen with chronic denervation, maybe with myopathies

Answer 3

Seen with myotonia congenita, radiculopathies, polyneuropathies, Disctinguished from complex repetitive discharges by waxing and waning frequency "Dive bomber" potentials

Answer 4

Recording and analysis of electric waveforms of biologic origin, elicited in response to electric or physiologic stimuli.

Answer 5

Orthodromic (normal direction) propagation of APs along a nerve, ACh release at NMJ and myofibre depolarization.

Answer 6

**Abnormal canine fibular motor nerve conduction study.** Note the polyphasia, temporal dispersion, and decrease in amplitude of the M-wave when compared with panel B. Motor nerve conduction velocities calculated in this 6-year-old dog were slowed: 39 m/s (hip to stifle) and 32 m/s (stifle to hock). These abnormalities are consistent with demyelination. **M waves at each site should have similar configuration.** Normal canine fibular motor nerve conduction study. Note that latency of the M-wave increases with greater distance between stimulating and recording electrodes. Motor nerve conduction velocities calculated in this 1-year-old dog were 69 m/s (hip to stifle) and 57 m/s (stifle to hock).

Answer 7

**MNCV (m/s) = Distance (mm) / (Proximal latency - Distal latency (ms))** Latencies are determined for each potential by marking the point at which the baseline deflects in an upward direction. Amplitudes may be measured between baseline and negative peak (although some investigators use negative-to-positive peak amplitude). Distances between the tips of the stimulating electrodes are measured to calculate nerve conduction velocities. It is this difference in distance over the difference in latency that determines the motor nerve conduction velocity, expressed in meters per second.

Answer 8

Fibular, tibial, radial, ulnar n. Keep patient warm as decreased temperature --\> slowed MNCV.

Answer 9

* Prolonged duration of deflection from - to baseline (i.e. increased wave width!) * Biphasic --\> polyphasic potential * (Diminished amplitude) * (Extreme slowing of MNCV)

Answer 10

Fibular, radial, ulnar. Why not tibial (like with motor conuction studies)? Because involve stimulation at a site where nerve is mixed

Answer 11

Sensory potential often polyphasic Somatosensory evoked potential study in a normal dog (B) and a dog with a sensorimotor polyneuropathy (C), following stimulation of the fibular nerve at the distal end of the fourth metatarsus (stimulus site). Somatosensory evoked potentials were recorded from the hock, stifle, hip, and L4-L5 (cord dorsum potential [CDP]). Latency measurements for sensory conduction velocity determinations are represented by T1, T2, T3, and T4. A, Diagram of electrode placement. B, Normal canine somatosensory evoked potential study. Although the somatosensory evoked potentials appear to be of similar amplitude at each recording site, the sensitivity increases from hock to L4-L5. Note that 1000 individual potentials (N = 1000 to right of figure) were averaged to produce these tracings

Answer 12

Abnormal canine somatosensory evoked potential study. All sensory nerve action potentials are severely reduced in amplitude, and sensory nerve conduction velocities are slowed. Dispersion of the potentials is difficult to evaluate because potentials are barely distinguishable from background noise. Note that compared with panel B, 4000 individual potentials (N = 4000) were averaged in an attempt to minimize random background noise from the time-locked electrical signal. These abnormalities are consistent with a severe sensory neuropathy.

Answer 13

* F waves (tests ventral nerve root) * H reflex (tests dorsal and ventral nerve root) Called *late responses* as have longer latency than M wave

Answer 14

Motor uses higher voltage (milivolts), n = 1 Sensory uses microvolts, uses average of several tests so look for n value!

Answer 15

Supramaximal stimulation --\> antidromic (reverse) motor nerve activation --\> additional volley in orthofromic direction therefore longer latency than m wave and latency longer the more distal the stimulation site (i.e. inverse to m wave latencies) Purely motor nerve testing A, Normal canine M-waves (left) and F-waves (right) recorded following fibular nerve stimulation at the hock (32 superimposed individual tracings). B, Normal canine M-waves (left) and F-waves (right) recorded following fibular nerve stimulation at the hip (32 superimposed individual tracings). Note the longer latency of the M-waves (left) and the reduced latency of the F-waves (right) compared with those in panel A.

Answer 16

Electrically elicited stretch reflex (i.e. like patella reflex) Afferent via sensory nerve efferent via motor nerve Normal canine H-waves recorded following fibular nerve stimulation at the hip using a low stimulus intensity (0.6 mA). Note that M-waves are not present (left). D, The same stimulation and recording sites as used in panel C, after a slight increase in stimulus intensity (to 1.0 mA). M-waves now are present (left).

Answer 17

Late waves assess function of most proximal segments of nerve.

Answer 18

* Repetitive Nerve Stimulation * Single Fibre Electromyography

Answer 19

Decremental response \>10% Repetitive nerve stimulation. at the hock. Note in the data table that M-wave amplitude (Peak amp mV), area under the M-wave (Area mVms), and percentage amplitude decrement (Amp decr %) remain constant with consecutive stimuli. B, Decremental response in a cat following 3-Hz fibular nerve stimulation at the hock. Note that amplitude and area under the M-wave decrease with consecutive stimuli, which is measured as a percentage amplitude decrement of 17% to 44%. The cat had muscular dystrophy. C, Facilitation in a dog following 30-Hz fibular nerve stimulation at the hock. Note that both area and amplitude of the M-wave are increased (i.e., the M-wave becomes taller and is more broad based). The increase in amplitude is represented by a negative Amp decr %. A cause could not be determined in this dog presenting with exercise-induced weakness that occurred in warm weather. D, *Pseudofacilitation* in a normal dog following 30-Hz fibular nerve stimulation at the hock. Note the increase in amplitude with no change in the area under the curve (i.e., the M-wave becomes taller and more narrow based). As in panel C, the increase in amplitude is represented by a negative Amp decr %.

Answer 20

Single fibre electromyography e.g. for aquired MG

Answer 21

Cranial tibial muscle

Answer 22

* Electron microscopy * Histo

Answer 23

common fibular nerve (or tibial or ulnar)

Answer 24

Proprioceptive deficits with knuckling

Chapter 27 Neurodiagnostics Flashcards

(48 cards)