Routine upper extremity conduction techniques Flashcards
Median motor study 1) recording sites 2) stimulation sites 3) distal distance
1) Recording Site:
Abductor pollicis brevis (APB) muscle (lateral thenar
eminence):
G1 placed over the muscle belly
G2 placed over the first metacarpal-phalangeal joint
2) Stimulation Sites:
Wrist: Middle of the wrist between the tendons to the
flexor carpi radialis and palmaris longus
Antecubital fossa: Over the brachial artery pulse
3) Distal Distance: 7 cm
In median motor study, what could a higher proximal amplitude mean
If the amplitude of the compound muscle action
potential (CMAP) is larger at the antecubital fossa
than at the wrist, consider a Martin–Gruber
anastomosis
Median palmar motor study: 1) Recording sites 2) stimulation sites 3) Distance
1) Recording Site:
Abductor pollicis brevis (APB) muscle:
G1 placed over the muscle belly
G2 placed over the first metacarpal–phalangeal joint
2) Stimulation Sites:
Wrist: Middle of the wrist between the tendons to the
flexor carpi radialis and palmaris longus at a distance of
7 cm from the recording electrode
Palm: Stimulate in the palm, 7 cm distal to the wrist site
on a line drawn from the median wrist to the web
space between the index and middle fingers
3) Distance:
7 cm from the wrist to the APB (wrist stimulation)
What can we test for with median motor palmar conduction study
A palm/wrist CMAP amplitude ratio >1.2 on median palmar conduction studies implies some conduction block across the wrist
Calculation of conduction velocity is not reliable
because of the short distances and the course of the
recurrent branch of the thenar motor branch.
Median sensory palmar study: 1) Recording site 2) stimulation sites and 3) proximal and distal distance 4) what can we test for
1) Recording Site:
Middle finger:
Ring electrodes with G1 placed over the proximal
interphalangeal joint
G2 placed over the distal interphalangeal joint
2) Wrist: Middle of the wrist between the tendons to the
flexor carpi radialis and palmaris longus at a distance of
14 cm
Palm: Stimulate in the palm, 7 cm distal to the wrist site
on a line drawn from the median wrist to the middle
finger
3) Distal Distance: 7 cm
Proximal Distance: 14 cm
4) A palm/wrist sensory nerve action potential (SNAP)
amplitude ratio >1.6 implies some conduction block
across the wrist.
Ulnar motor study: 1) recording sites 2) stimulation sites 3) distal distance
1) Recording Site:
Abductor digiti minimi (ADM) muscle (medial hypothenar eminence):
G1 placed over the muscle belly
G2 placed over the fifth metacarpal–phalangeal joint
2) Wrist: Medial wrist, adjacent to the flexor carpi ulnaris
tendon
Below elbow: 3 cm distal to the medial epicondyle
Above elbow: Over the medial humerus, between the
biceps and triceps muscles, at a distance of 10–12 cm
from the below-elbow site
Axilla (optional): In the proximal axilla, medial to the
biceps over the axillary pulse
3) Distal distance: 7cm
Which is the optimal position of the elbow in the ulnar motor conduction studies and why
The optimal position is with the elbow flexed between
90° and 135°.
If performed in a straight-elbow
position, factitious slowing across the elbow will be
seen due to underestimation of the true nerve length
Which is the optimal below elbow stimulaton site for ulnar motor conduction study and why
Stimulation must be at least 3 cm distal to the medial
epicondyle at the below-elbow site to ensure that
stimulation is distal to the cubital tunnel, a common
site of ulnar nerve compression at the elbow.
However, if stimulation at the below-elbow site is
too distal (>4 cm), the nerve is very deep and very
difficult to stimulate, reinforcing that the optimal
stimulation site is 3 cm distal to the medial
epicondyle.
In ulnar motor studies, what could a smaller below elbow CMAP amplitude comparing to wrist mean
If the CMAP amplitude at the below-elbow site is
more than 10% smaller than that at the wrist,
consider a Martin–Gruber anastomosis
What should we keep in mind during antidromic sensory studies
A volume-conducted motor potential occasionally may
obscure the sensory potential in antidromic studies.
If this occurs, have the patients slightly spread their
fingers and stimulate again
In which cases can a ulnar sensory study be abnormal
May be abnormal in ulnar neuropathy or lower trunk brachial plexopathy (e.g., thoracic outlet syndrome).
Dorsal Ulnar cutaneus study: 1) stimulation site, 2) what can be used for and 3) in which cases is always spared
1) Slightly proximal and inferior to the ulnar styloid with
the hand pronated
2) Often helpful to compare side-to-side amplitudes in
cases where one side is symptomatic and the other is
not
3) Always spared in lesions of the ulnar nerve at Guyon’s canal
Deep ulnar motor conduction study: 1) Recording site 2) when is it performed
1) First dorsal interosseous (FDI) muscle (dorsal web space between the thumb and index finger)
2) The deep ulnar motor branch often is preferentially
affected in lesions of the ulnar nerve at Guyon’s canal
Radial motor study: 1) Recording and 2) stimulation sites
1) Extensor indicis proprius (EIP) muscle:
With hand pronated, G1 placed two fingerbreadths
proximal to the ulnar styloid
G2 placed over the ulnar styloid
2) Forearm: Over the ulna, 4–6 cm proximal to the active recording electrode
Elbow: In the groove between the biceps and brachioradialis muscles
Below spiral groove: Lateral midarm, between the biceps and triceps muscles
Above spiral groove: Posterior proximal arm over the
humerus
Radial motor study: 1) characteristic of its CMAP and 2) when is the study useful
1) The radial CMAP usually has an initial positive
deflection due to other nearby radial-innervated
muscles; thus, no need to change the active recording
electrode site to try to get on the motor point
2) Useful in the diagnosis and assessment of posterior
interosseous neuropathy and especially radial neuropathy at the spiral groove
