Chapter 19 Ulnar Neuropathy Flashcards
Compared to median neuropathy is it easy or difficult to localize ulnar neuropathy?
Difficult many must be described as non-localizable
Is the ulnar groove the same thing as the cubital tunnel?
No. Ulnar groove is between the medial epicondyle and the olecranon process. The cubital tunnel is distal to the ulnar groove.
What structures form the cubital tunnel?
The cubital tunnel is formed from the tendinous arch of the two heads of the flexor Carpi ulnaris muscle.
Does cubital tunnel entrapment spare the flexor carpi ulnaris?
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.
Name all ulnar innervated muscles proximal to the wrist.
Flexi carpi ulnaris and the
flexor digitorum profundus to digits four and five.
How far distal to the elbow must you stimulate in order to ensure you are distal to the entrance of the cubital tunnel?
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.
What an event usually precedes tardy ulnar nerve palsy by many years?
Tarty ulnar palsy results from elbow fracture followed by arthritic changes that compress the ulnar nerve at the ulnar groove.
What treatment for an elbow fracture could result in a less tardy ulnar palsy?
Compression by the cast.
What does someone with congenitally tight cubital tunnel do to put themselves at risk for cubital tunnel syndrome?
Frequent and persistent elbow flexion
In carpal tunnel syndrome sensory symptoms are more prominent than motor. is this also true with ulnar neuropathy at the elbow?
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.
Described benediction posture
- 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.
Describe Wartenberg’s sign
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.
Describe froment’s sign
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.
If a patient with in an ulnar nerve neuropathy has numbness on the dorsum of the hand, how does this help you localized lesion?
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.
Name the provocative test of ulnar neuropathy besides Tinel’s at the elbow.
Cubital tunnel syndrome maybe provoked by elbow flexion.
Radiculopathy of which roots may be difficult to distinguish from ulnar Neuropathy?
C8 or t1
Which is more difficult to localize: an ulnar lesion resulting in demyelination or in axonal loss?
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.
What elbow position allows for best measurement of the ulnar nerve across the elbow?
To avoid falsely slowed conduction velocity across the elbow, measure that ulnar nerve with the elbow flexed.
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?
Deltas of greater than 10 to 11 m/s are abnormal.
Which is better at detecting abnormalities at the elbow: differential conduction velocity or absolute conduction velocity across the elbow?
Some Authors believe that a better measure of UL NARneuropathy across the elbow is low absolute conduction velocity.
What is the lower limit of normal for conduction velocities across the elbow?
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.
Compare ulnar finger SNAPs in the situations of pure demyelination and axonal loss.
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.
What are the two NCS findings, Either one of which localizes ulnar neuropathy?
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.
What positive findings on NCS are consistent with a non-localizable ulnar lesion with only axonal loss?
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.
What decrement of CMAP amplitude between below and above elbow stimulation is consistent with conduction block?
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.
What decrement of CMAP amplitude between wrist and above elbow stimulation is consistent with conduction block?
To qualify for conduction block, CMAP amplitude when comparing wrist and above elbow should drop by 25%.
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?
The ulnar groove is stimulated at 1 cm intervals in each direction from the ulnar groove.
What decrement in distal latency with 1 cm inching is considered significant?
As stimulation moves proximally 1 cm, distal latency increases of .5 ms or more is abnormal and suggests a focal demyelination.
Name one circumstance in which it is clinically relevant whether the entrapment is at the ulnar groove or at the cubital tunnel.
If the patient is considering surgery, location is important. Cubital tunnel entrapment maybe better treated with the release instead of nerve transposition.
Studies support which CMAP as the most sensitive in detecting ulnar neuropathy at the elbow?
Preston says some studies show that a slightly more sensitive the CMAP is from the FDI.
Where do you place the reference electrode for CMAPs?
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.
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?
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.
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?
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.
Which finding would be more helpful in localizing an ulnar lesion: a dorsal ulnar cutaneous snap that is present or absent?
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.
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?
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.
What is the ideal distance between below elbow and above elbow stimulation sites?
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.
If ulnar CMAP amplitudes are much higher at the wrist compared to below the elbow, what class of pathology would explain this?
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.
What is the most likely explanation for ulnar CMAP amplitudes that are much higher at the wrist compared to the elbow?
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.
What NCS must be done if you find ulnar CMAP amplitudes are much higher at the wrist compared to the below the elbow?
To rule out Martin – Gruber anastomosis, do CMAPS of the median proximally and distally.
Name three ulnar – Innervated muscles that might be studied on EMG and work up of ulnar neuropathy.
FCU, ADM and FDI
Name three non-– ulnar muscles that might be easily needled to exclude C8 – T1 radiculopathy.
3 non ULNAR muscles of that might be needled to exclude C8- T1 radiculopathy include: FPL, APB and EIP.
Which is better tolerated: needling of ADM or FDI?
Preston says patients tolerate FDI
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?
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.
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?
You can distinguish a non-localizable ulnar neuropathy from a medial cord plexopathy if you find a normal medial antebrachial cutaneous SNAP.
