Chapter 19 Ulnar Neuropathy

Question 1

Compared to median neuropathy is it easy or difficult to localize ulnar neuropathy?

Answer 1

Difficult many must be described as non-localizable

Question 2

Is the ulnar groove the same thing as the cubital tunnel?

Answer 2

No. Ulnar groove is between the medial epicondyle and the olecranon process. The cubital tunnel is distal to the ulnar groove.

Question 3

What structures form the cubital tunnel?

Answer 3

The cubital tunnel is formed from the tendinous arch of the two heads of the flexor Carpi ulnaris muscle.

Question 4

Does cubital tunnel entrapment spare the flexor carpi ulnaris?

Answer 4

The branches of the FCU travel in the cubital tunnel yet are usually spared or only mildly affected in the ulnar neuropathy at the elbow. It Isn’t known why but in General compression neuropathies are more often seen to affect distal muscles more.

Question 5

Name all ulnar innervated muscles proximal to the wrist.

Answer 5

Flexi carpi ulnaris and the

flexor digitorum profundus to digits four and five.

Question 6

How far distal to the elbow must you stimulate in order to ensure you are distal to the entrance of the cubital tunnel?

Answer 6

The distance Between the ulnar groove and the entrance of the cubital tunnel vary Between people, but no more than 2 cm Between the ulnar groove and the start of the cubital tunnel. Preston says Stimulate at least 3 cm distal to the elbow.

Question 7

What an event usually precedes tardy ulnar nerve palsy by many years?

Answer 7

Tarty ulnar palsy results from elbow fracture followed by arthritic changes that compress the ulnar nerve at the ulnar groove.

Question 8

What treatment for an elbow fracture could result in a less tardy ulnar palsy?

Answer 8

Compression by the cast.

Question 9

What does someone with congenitally tight cubital tunnel do to put themselves at risk for cubital tunnel syndrome?

Answer 9

Frequent and persistent elbow flexion

Question 10

In carpal tunnel syndrome sensory symptoms are more prominent than motor. is this also true with ulnar neuropathy at the elbow?

Answer 10

In ulnar neuropathy at the elbow, motor symptoms are more prominent sensory, especially in chronic cases. Patients often seek medical attention because of reduced dexterity.

Question 11

Described benediction posture

Answer 11

• Finger abduction weakness (interossei) and
• clawing of digits 4 & 5 (Extension at the metacarpophalangeal joints and
• flexion of the distal and proximal interphalangeal joints from weakness of the third and fourth lumbricals.

Question 12

Describe Wartenberg’s sign

Answer 12

This sign results from difficulty ADD ducting the fifth digit or because of preferential weakness in the third Palmer interosseous muscle. Notice the finger is held abducted.

Question 13

Describe froment’s sign

Answer 13

Weakness of the ulnar Innervated adductor pollicis,
deep head of the flexor Pollis brevis and interossei results in weakness of pinch.

To Compensate the median innervated flexor pollicis longis and flexor digitorum profundis have to contract.

Question 14

If a patient with in an ulnar nerve neuropathy has numbness on the dorsum of the hand, how does this help you localized lesion?

Answer 14

The mediodorsal hand is supplied by the dorsal ulnar cutaneous sensory branch, which branches from the ulnar nerve 5 to 8 cm proximal to the wrist. Numbness in this distribution with muscle abnormalities implies that a solitary lesion would be proximal to the wrist.

Question 15

Name the provocative test of ulnar neuropathy besides Tinel’s at the elbow.

Answer 15

Cubital tunnel syndrome maybe provoked by elbow flexion.

Question 16

Radiculopathy of which roots may be difficult to distinguish from ulnar Neuropathy?

Answer 16

C8 or t1

Question 17

Which is more difficult to localize: an ulnar lesion resulting in demyelination or in axonal loss?

Answer 17

It is more difficult to localize a lesion if it results in axonal loss. Conduction block or slowing can sometimes Be localized with nerve conduction studies.

Question 18

What elbow position allows for best measurement of the ulnar nerve across the elbow?

Answer 18

To avoid falsely slowed conduction velocity across the elbow, measure that ulnar nerve with the elbow flexed.

Question 19

Normally proximal conduction velocities are faster. If the above the elbow conduction velocity is slower than the forearm velocity, what is the largest differential that is normal?

Answer 19

Deltas of greater than 10 to 11 m/s are abnormal.

Question 20

Which is better at detecting abnormalities at the elbow: differential conduction velocity or absolute conduction velocity across the elbow?

Answer 20

Some Authors believe that a better measure of UL NARneuropathy across the elbow is low absolute conduction velocity.

Question 21

What is the lower limit of normal for conduction velocities across the elbow?

Answer 21

Conduction velocity across the elbow lower than 49 m/s is abnormal. Some authors believe that a better measure of ulnar neuropathy across the elbow is low absolute conduction velocity, i.e. less than 49 m/s.

Question 22

Compare ulnar finger SNAPs in the situations of pure demyelination and axonal loss.

Answer 22

In pure demyelination, ulnar snaps are normal. With axonal involvement, snap amplitudes are reduced distally and distal latency May be prolonged. The same findings in CMAPs help clarify the distinction of axonal versus demyelinating versus both.

Question 23

What are the two NCS findings, Either one of which localizes ulnar neuropathy?

Answer 23

NCS localize neuropathy by demonstrating conduction block or a focal slowing. Without demonstration of either conduction block or focal slowing, the lesion is not localizable.

Question 24

What positive findings on NCS are consistent with a non-localizable ulnar lesion with only axonal loss?

Answer 24

A non-localizable lesion with only axonal loss would result in reduced CMAP and SNAP amplitudes with mildly prolonged distal latency and mildly reduced conduction velocities.

Question 25

What decrement of CMAP amplitude between below and above elbow stimulation is consistent with conduction block?

Answer 25

To qualify for conduction block, CMAP amplitudes when comparing below and above elbow should drop by 10%. There is controversy about thresholds for conduction block.

Question 26

What decrement of CMAP amplitude between wrist and above elbow stimulation is consistent with conduction block?

Answer 26

To qualify for conduction block, CMAP amplitude when comparing wrist and above elbow should drop by 25%.

Question 27

The technique of inching around the elbow requires mapping of the ulnar nerve to maximize CMAP at low stimulation, usually 10 to 25%of Supramaximal. Once the nerve is mapped, What is the distance interval for supramaximal stimulation?

Answer 27

The ulnar groove is stimulated at 1 cm intervals in each direction from the ulnar groove.

Question 28

What decrement in distal latency with 1 cm inching is considered significant?

Answer 28

As stimulation moves proximally 1 cm, distal latency increases of .5 ms or more is abnormal and suggests a focal demyelination.

Question 29

Name one circumstance in which it is clinically relevant whether the entrapment is at the ulnar groove or at the cubital tunnel.

Answer 29

If the patient is considering surgery, location is important. Cubital tunnel entrapment maybe better treated with the release instead of nerve transposition.

Question 30

Studies support which CMAP as the most sensitive in detecting ulnar neuropathy at the elbow?

Answer 30

Preston says some studies show that a slightly more sensitive the CMAP is from the FDI.

Question 31

Where do you place the reference electrode for CMAPs?

Answer 31

Place the reference for FDI CMAPS on the first MCP joint; placing it on the second MCP may cause an initial positive deflection that complicates latency measurements.

Question 32

You may detect ulnar neuropathy at the elbow measuring SNAPS tO digit five above and below the elbow. Is this technique better suited for diagnosing mild or severe cases?

Answer 32

Measuring snaps to digit five above and below the elbow is best at detecting mild cases. Severe cases may have such a low amplitude that the measurements are technically challenging.

Question 33

When using snaps to digit five above and below the elbow to detect ulnar neuropathy at the elbow, what perimeter of the study is being compared?

Answer 33

Because temporal dispersion dramatically reduces amplitudes of proximal snaps in normal subjects, amplitude cannot be used to screen for pathology. Instead one looks for focal slowing in conduction velocity.

Question 34

Which finding would be more helpful in localizing an ulnar lesion: a dorsal ulnar cutaneous snap that is present or absent?

Answer 34

The dorsal ulnar cutaneous nerve maybe normal in lesions at the elbow, so if it is normal differential is not clarified. When it’s Absent it points to a lesion proximal to the wrist.

Question 35

If the Ulnar nerve is stimulated less than 3 cm distal to the ulnar groove, you may miss cubital tunnel syndrome. If it is stimulated more than 4 cm distal to the ulnar groove, what to pitfalls could you face?

Answer 35

If the ulnar nerve is stimulated more than 4 cm distal to the ulnar groove, a high Martin Gruber anastomosis could give a false positive for conduction block. This is because ulnar fibers running with the median nerve and eventually rejoin the ulnar nerve, thus abruptly increasing CMAP amplitudes in the same way that conduction block would.

The second pitfall is that the nerve and deeper distally and full stimulation may not be possible potentially giving a false negative for conduction block.

Question 36

What is the ideal distance between below elbow and above elbow stimulation sites?

Answer 36

The ideal distance between below elbow and above elbow stimulation site is 10 cm. Less than this risks measurement error. More than this risk diluting the impact of local demyelination.

Question 37

If ulnar CMAP amplitudes are much higher at the wrist compared to below the elbow, what class of pathology would explain this?

Answer 37

If ulnar CMAP amplitudes are much higher at the wrist compared to the elbow, the pathology that would explain this would be a conduction block in the forearm. This is very rare.

Question 38

What is the most likely explanation for ulnar CMAP amplitudes that are much higher at the wrist compared to the elbow?

Answer 38

Ulnar conduction block in the forearm is very rare. It’s important to think about it because rarely people have undergone surgeries at the elbow when the block was from compression from an anomalous vascular bundle in the forearm. Far more common than conduction block is a non-pathological cause: Martin– Gruber anastomosis.

Question 39

What NCS must be done if you find ulnar CMAP amplitudes are much higher at the wrist compared to the below the elbow?

Answer 39

To rule out Martin – Gruber anastomosis, do CMAPS of the median proximally and distally.

Question 40

Name three ulnar – Innervated muscles that might be studied on EMG and work up of ulnar neuropathy.

Answer 40

FCU, ADM and FDI

Question 41

Name three non-– ulnar muscles that might be easily needled to exclude C8 – T1 radiculopathy.

Answer 41

3 non ULNAR muscles of that might be needled to exclude C8- T1 radiculopathy include: FPL, APB and EIP.

Question 42

Which is better tolerated: needling of ADM or FDI?

Answer 42

Preston says patients tolerate FDI

Question 43

If NCS failed to show focal Slowing or conduction block and needle exam is abnormal for all ULNAR muscles, what is the most likely pathology, and what do you say in your report?

Answer 43

In the case of the non-diagnostic NCS and abnormal needle exam of all ulnar muscles, the most likely cause is still ulnar neuropathy at the elbow, but your report must call it non-localizable.

Question 44

What nerve conduction study that is not part of the standard upper limb studies can help distinguish a non-localizable ulnar neuropathy from a medial cord plexopathy?

Answer 44

You can distinguish a non-localizable ulnar neuropathy from a medial cord plexopathy if you find a normal medial antebrachial cutaneous SNAP.