Ch 19: Ulnar Neuropathy At The Elbow

Front 1

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

Back 1

(291) Compared to median neuropathy, it’s difficult to localize ulnar neuropathy. Many must be described as non-localizable.

Front 2

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

Back 2

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

Front 3

3. What structures form the cubital tunnel?

Back 3

(291) The cubital tunnel is formed from the tendinous arch of the two heads of the flexor carpi ulnaris muscle.

Front 4

4. Most entrapment neuropathies spare the muscle which entraps them. Does cubital tunnel entrapment spare the flexor carpi ulnaris?

Back 4

(293, 306) The branches to the FCU travel in the cubital tunnel yet are usually spared or only mildly affected in ulnar neuropathy at the elbow. It isn’t known why, but in general compression neuropathies are seen to affect distal muscles more.

Front 5

5. Name all ulnar-innervated muscles proximal to the wrist.

Back 5

. (291) Proximal to the wrist, the ulnar-innervated muscles are the flexor carpi ulnaris and the flexor digitorum profundus to digits 4 and 5.

Front 6

6. How far distal to the elbow must you stimulate to be sure that you are stimulating distal to the entrance of the cubital tunnel?

Back 6

(293) The distance between the ulnar groove and the start of the cubital tunnel varies between people but is no more than 2 centimeters. Preston says to stimulate at least three centimeters distal to the elbow for your below-elbow measurement.

Front 7

7. What event usually precedes tardy ulnar palsy by many years?

Back 7

? (293) Tardy ulnar palsy results from elbow fracture followed by arthritic changes that compress the ulnar nerve at the ulnar groove.

Front 8

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

Back 8

(293) Rather than wait many years for osteoarthritis to give you your tardy ulnar palsy, you can get one after a fracture from compression by the cast. Casting can compress the ulnar nerve.

Front 9

9. Although some people use the phrase ‘cubital tunnel syndrome’ to refer to all lesions of the ulnar nerve at the elbow, it more properly refers to compression within the tunnel itself. What does a person with a congenitally tight cubital tunnel do to put themselves at higher risk for compression at the cubital tunnel?

Back 9

293) If you’ve got a tight cubital tunnel, you can get neuropathy from pressure as a result of frequent and persistent elbow flexion.

Front 10

10. In CTS, sensory symptoms are more prominent than motor. Is this also true with ulnar neuropathy at the elbow?

Back 10

(293) In ulnar neuropathy at the elbow, motor symptoms are more prominent than sensory, especially in chronic cases. These patients seek medical attention not because of paresthesias but because of reduced dexterity

Front 11

12. If a patient with ulnar neuropathy has numbness on the dorsum of the hand, how does this help you localize the lesion?

Back 11

(293) The dorsal medial hand is supplied by the dorsal ulnar cutaneous sensory branch, which branches from the ulnar nerve five to eight centimeters proximal to the wrist. Numbness in this distribution with muscle abnormalities implies that a solitary lesion would be proximal to the wrist.

Front 12

13. Name a provocative test of ulnar neuropathy besides Tinnel’s at the elbow.

Back 12

. (295) Cubital tunnel syndrome may be provoked by elbow flexion.

Front 13

14. Radiculopathy of which roots may be difficult to distinguish from ulnar neuropathy? (295)

Back 13

It may be difficult to distinguish ulnar neuropathy from radiculopathy of C8 and or T1.

Front 14

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

Back 14

(296) It is more difficult to localize the lesion if it results in axonal loss. Conduction block or slowing can sometimes be localized with NCS.

Front 15

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

Back 15

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

Front 16

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

Back 16

(298) Deltas of greater than 10 to 11 m/s are abnormal

Front 17

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

Back 17

(298) Some authors believe that a better measure of ulnar neuropathy across the elbow is low absolute conduction velocity.

Front 18

19. What is the lower limit of normal for conduction velocity across the elbow? (298)

Back 18

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

Front 19

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

Back 19

(298) In pure demyelination, ulnar SNAPs are normal. With axonal involvement, SNAP amplitudes are reduced and distal latencies may be prolonged. These same findings in CMAPs help clarify the distinction of axonal vs demyelinating vs both.

Front 20

21. What are the 2 NCS findings, either one of which localizes ulnar neuropathy?

Back 20

(298) 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.

Front 21

22. What positive findings on NCS are consistent with a nonlocalizable ulnar lesion with only axonal loss?

Back 21

(298) A nonlocalizable lesion with only axonal loss would result in reduced CMAP and SNAP amplitudes with mildly prolonged distal latencies and mildly reduced conduction velocities.

Front 22

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

Back 22

(300) To qualify for conduction block, CMAP amplitude when comparing below and above elbow should drop by 10%. Preston admits that there is some controversy about thresholds for conduction block.

Front 23

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

Back 23

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

Front 24

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

Back 24

(300) The ulnar nerve is stimulated at 1 cm intervals in each direction from the ulnar groove.

Front 25

26. What decrement in distal latency with 1cm “inching” is considered significant?

Back 25

300) As stimulation moves proximally 1cm, distal latency increase of 0.5ms or more is abnormal and suggests a focal demyelination.

Front 26

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

Back 26

(300) If a patient is considering surgery, location is important. Cubital tunnel entrapements may be better treated with release instead of nerve transposition.

Front 27

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

Back 27

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

Front 28

29. Where do you place the reference electrode for FDI CMAPs?

Back 28

(301) 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.

Front 29

30. 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?

Back 29

(302) Measuring SNAPs to digit five above and below the elbow is best at detecting mild cases. Severe cases may have such low amplitudes that measurements are technically challenging.

Front 30

31. When using SNAPs to digit five above and below the elbow to detect ulnar neuropathy at the elbow, what parameter of the study is being compared?

Back 30

(303) Because temporal dispersion dramatically reduces amplitudes of proximal SNAPs in normal subjects, amplitude can not be used to screen for pathology. Instead one looks for focal slowing in conduction velocity.

Front 31

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

Back 31

(303) The dorsal ulnar cutaneous nerve may be normal in lesions at the elbow, so if it is normal the differential isn’t clarified. When it is absent, it points to a lesion proximal to the wrist.

Front 32

33. 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 2 pitfalls could you face?

Back 32

(305) If the ulnar nerve is stimulated more than 4 cm distal to the ulnar groove, a high Martin-Gruber anastamoses could give a false positive for conduction block. This is because ulnar fibers running with the median nerve eventually rejoin the ulnar nerve, thus abruptly increasing CMAP amplitude in the same way that conduction block would. The second pitfall is that the nerve runs deeper distally and full stimulation may not be possible, potentially giving a false negative for conduction block.

Front 33

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

Back 33

(305) The ideal distance between below-elbow and above-elbow stimulation sites is 10 centimeters. Less than this risks measurement error. More than this risks diluting the impact of focal demyelination.

Front 34

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

Back 34

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

Front 35

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

Back 35

(305) 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.

Front 36

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

Back 36

(305) To rule out Martin-Gruber anastomosis, do CMAPs of the median proximally and distally.

Front 37

38. Name 3 ulnar-innervated muscles that might be studied on EMG in work-up of ulnar neuropathy.

Back 37

. (305) Three ulnar-innervated muscles that might be studied on EMG in work-up of ulnar neuropathy are: FCU, ADM and FDI.

Front 38

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

Back 38

(305). Three non-ulnar muscles that might be needled to exclude a C8-T1 radiculopathy include: FPL, APB and EIP.

Front 39

40. Which is better tolerated: needling of ADM or FDI?

Back 39

(305) Preston says patients better tolerate needling of FDI.

Front 40

41. If NCS fail 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?

Back 40

(306) In the case of 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 nonlocalizable.

Front 41

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

Back 41

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