Nerve conduction study

Nerve conduction study Nerve conduction study - ANS -recording of evoked responses produced by electrically stimulating a nerve. -to see if the nerve is conducting an impulse slower than normal -If there is a decrease in conduction velocity (speed) then there will be an increase in latency (time). Clinical questions for NCS - ANS Are peripheral nerve fibers compromised? Are sensory fibers, motor fibers, autonomic fibers or all three involved? Where is the nerve lesion? How many nerves are involved? Is the nerve involvement in one limb or bilateral? Are UE and LE nerves involved? Is the lesion partial or complete? Is the nerve impairment recovering or degenerating? Is the problem a local nerve block, axonal degeneration, or demyelination? Does the pattern or involvement suggest a single nerve (mononeuropathy) or many nerves (polyneuropathy)? Polyneuropathies are usually symmetrical. When many nerves are involved unsymmetrically, it is called polyneuropathy multiplex Mononeuropathy - ANS one nerve is involve polyneuropathy - ANS more than one nerve but usually in a symmetrical pattern. For example, diabetic polyneuropathy: both sural nerves multiplex - ANS nerves are involved unsymmetrically: mononeuropathy- right median nerve and left peroneal nerve (only one of each) polyneuropathy- many nerves are involved in a unsymmetrical pattern What is clinical sensory testing? - ANS -done prior to ENMG testing -to assist directing of ENMG -includes 2 tests: Semmes-Weinstein monofilament test and 2 point discrimination What motor nerves are commonly studied in the UE using NCS? Sensory nerves? - ANS M: median, ulnar, deep radial, axillary, suprascapular S: median, ulnar, superficial radial, medial antebrachial cutaneous (medial cutaneous of forearm), lateral antebrachial cutaneous (lateral cutaneous forearm), dorsal ulnar cutaneous What is the process for motor nerve conduction study? - ANS Surface electrodes on distal muscle Peripheral nerve stimulated 8-12 cm away from cathode, then NCV/amplitude of evoked response determined Compare NCV to normative values to determine location/extent of injury/demyelination Certain nerves studied much more extensively than others F-wave (antidromic) - used in proximal nerve injuries What is the process for median nerve motor study? - ANS The active recording electrode are place over the abductor pollicis brevis. Reference (inactive) electrode is placed 3 cm distal to the active recording electrode. A ground electrode is placed on the back of the hand. The stimulating electrode is placed at least 8 cm proximal to the recording electrode over the median nerve. This electrode may also be at the elbow or in the axilla. Compound motor action potentials (CMAP) are always larger than sensory because CMAPs are the summation of motor action potentials. What is the process for sensory nerve conduction study? - ANS Surface/ring electrode placed on skin directly over nerve trunk - SNAP stimulated Significantly smaller response than CMAP Similar procedure as motor nerve conduction Distal sensory latency, amplitude, waveform, duration, and NCV all determined H-reflex: takes a closer look at peripheral nerve dysfunction What is the process for orthodromic conduction sensory study median nerve? - ANS Two ring electrodes are placed on the index finger. The proximal electrode is the cathode, the distal electrode is the anode. These are the stimulating electrodes. Recording electrodes are placed along the median nerve at the wrist, elbow, or axilla. A ground electrode is on the dorsum (back) of the hand. Note: NCV studies generate action potentials that can propagate (move) orthodromically and antidromically along a nerve. What is the process for antidromic conduction sensory study median nerve? - ANS The ring electrodes are placed the same as in the orthodromic study, but now the electrodes are recording devices not stimulating electrodes. The stimulating electrode is placed proximal to the ring electrodes. The ground electrode is placed as in the orthodromic study. When testing for carpal tunnel syndrome, what would you expect? how would you depict between mild and moderate? - ANS -sensory testing: slowing of the conduction speed (increase or prolonged sensory latency). -EMG testing of abductor pollicis brevis: no abnormal findings -motor: mild=normal findings; moderate= slowing of the conduction speed (increase or prolonged sensory latency) What reasons/conditions affect nerve conduction velocity? - ANS 2 primary reasons (reduced NCV): mechanical compression of the nerve (CTS) and demyelination of axons (MS) 2 conditions: temperature (slows speed) and age (slower speeds in children and elderly) What motor nerves are commonly studied in the LE using NCS? Sensory nerves? - ANS M: tibial, deep fibular (peroneal), femoral S: tibial, superficial fibular (peroneal), sural Motor APs are ____ in nerve injuries, neuropathies, and myopathies. - ANS decreased Different neuromuscular disorders can produce ____ in amplitudes of motor and sensory action potentials. - ANS reductions How can sensory APs in NCV be reduced? - ANS due to compression injuries and demylination Motor amplitudes are always ____ than sensory. - ANS larger H-reflex - ANS -with F-wave: study the proximal portion of the nerve -analogous to the Achilles tendon reflex test -look at peripheral nerve dysfunction -Ia afferent axons carry the stimulus to the spine where the stimulus synapses with A alpha motor fibers in the tibial nerve. -impulse synapses at the NMJ at the soleus muscle and the recording is analyzed. -Stimulation is at sensory level not supramaximal (sub) -electrical equivalent of the monosynaptic stretch reflex -only a few muscles -used in gastroc and soleus (MC) and flexor carpi radialis superficialis and the quadriceps. -latency: 34 m/sec. -evaluates conduction between the limb and the spinal cord -uses stimulation of the sensory portion of a nerve and recording the reflexive electrical discharge from a muscle in the limb -SAME axon reflex - ANS small motor potential that is seen in re-innervated muscles. M response - ANS seen when muscle contracts with electrical stim What are some of the late response with NCS? - ANS f wave, h reflex, axon reflex F wave - ANS -with H-reflex: study the proximal portion of the nerve -compound muscle action potential seen in stimulation of motor nerves -result from the antidromic propagation of action potentials in motor axons. -occurs at the interface of the PNS and the CNS. -variable and at least 10 waves should be obtained and the shortest is measured -UE: 25 - 32 m/sec -LE: 45 - 56 m/sec -prolonged due to: A lesion of the proximal nerve segment, Abnormal distal motor latency, or An unusually tall patient -done a supramaximal stimulation -Jendrassik maneuver may be used to prime the anterior horn cells. -evaluates NCV between the limb and spine, whereas the MNCS and SNCS studies evaluate conduction in the limb -not reflex -Nerve potential travels from site of stimulating electrode in limb to SC and back to a muscle in limb in same nerve that was stimulated What are the 5 involvements that commonly affect F wave latency? - ANS Demyelinating polyneuropathy (Guillain-Barre syndrome). Amyotrophic lateral sclerosis. Myotonic dystrophy. Entrapment neuropathies (TOS, CTS) Brachial or lumbosacral plexopathy What's the difference between F wave and H reflex? - ANS F wave supramaximal electrical stimulation H-reflex: submaximal Myasthenia Gravis - ANS -autoimmune disorder that causes weakness. -caused by antibodies that block acetylcholine receptors at the post synaptic NMJ. -starts in facial muscles -untreated: death by respiratory failure Blink reflex - ANS -assesses: Ophthalmic division of Cranial Nerve V (trigeminal nerve) and VII (facial nerve) -conditions that affect them: Guillain-Barre syndrome, Bell's palsy, tumors at the cerebellar-pontine angle, brainstem aneurysms, acoustic neuromas, and multiple sclerosis. -example: Bell's palsy= the involved side blink reflex will be prolonged, but the uninvolved side will be normal; MS= both sides will usually demonstrate prolonged blink reflex responses Somatosensory evoked potentials - ANS -evaluate CNS -orthodromic at wrist in UE and recorded supraclavicular and at skull over the sensory cortex -tests the A beta fibers associated with touch & pressure, the dorsal column medial lemnicus pathway, and the sensory cortex. Motor evoked potentials - ANS -tests descending motor pathways -activates motor cortex along the lateral corticospinal paths -test peripheral motor axons and skeletal muscles -Transcutaneous stimulation was used in the early stages of testing. Now, magnetic stimulation is the preferred method.