Ulnar Neuropathy Workup

Updated: May 23, 2017
  • Author: Charles F Guardia, III, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Workup

Laboratory Studies

Routine studies for ulnar nerve entrapment are ordered to rule out anemia, diabetes mellitus, and hypothyroidism and include the following:

  • Complete blood cell (CBC) count
  • Urinalysis
  • Fasting blood glucose

Depending on the specific clinical situation, the following tests may be considered as well:

  • Hemoglobin A 1C [111]
  • Antinuclear antibody
  • Erythrocyte sedimentation rate
  • Renal function tests
  • Paraproteinemia workup (serum protein electrophoresis with immunofixation)
  • Angiotensin-converting enzyme
  • Lyme serology
  • Thyroid function tests
  • Vitamins B-12, B-1, and B-6
  • Folate level
  • Methylmalonic acid
  • Tissue transglutaminase antibody
  • Gliadin antibody
  • HIV serology
  • Hepatitis serologies
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Radiography

Radiographs of the neck should be obtained if cervical disk disease is suspected and to rule out cervical ribs. Radiographs of the chest should be obtained if Pancoast tumor or tuberculosis is suspected.

Radiographs of both the elbow and the wrist are mandatory in ulnar nerve compression because double-crush syndrome may be present. Entrapment of the ulnar nerve may occur at more than one level.

Radiographs of the elbow reveal abnormal anatomy, such as a valgus deformity, bone spurs or bone fragments, a shallow olecranon groove, osteochondromas, and destructive lesions (eg, tumors, infections, or abnormal calcifications). If there is a history of trauma or arthritis, a cubital tunnel projection radiograph should be obtained to exclude medial trochlear lip osteophytes. If a supracondylar process on the medial aspect of the humerus is suspected, an elbow radiograph should be obtained 5 cm proximal to the medial epicondyle.

Radiographs of the wrist reveal fractures of the hook of the hamate, dislocations of the wrist bones, and, to a lesser extent, soft-tissue masses and calcifications.

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Ultrasonography

Ultrasonographic examination of peripheral nerves may be used to support the clinical and electrophysiologic diagnosis in a compressive neuropathy. It may also help in identifying specific compressive etiologies of nerve injury (eg, tumors or cysts) and visualizing structural nerve changes. Advantages of ultrasonography include the following:

  • Unlike computed tomography (CT) or magnetic resonance imaging (MRI), ultrasonography provides real time evaluation of nerve displacement or compression during movements of adjacent joints
  • Ultrasonography is noninvasive, cheap, portable, and well tolerated
  • Ultrasonography is readily available (though technicians with specific experience in peripheral nerve ultrasonography may not be)
  • The peripheral nerve can be followed for much of its course in an extremity [112, 113, 114, 115, 116]

The ultrasonographic finding that seems to be most useful in this setting is a change in the diameter of a nerve at the site of compression. Just proximal to the site of compression, swelling of the nerve can often be seen.

A small study suggested that using a ratio of the cross-sectional nerve area at the site of maximal enlargement and at an uninvolved site could improve diagnostic accuracy. [117] Using this ratio did not improve diagnostic accuracy over what could be achieved simply by looking for the point of maximal swelling; however, the ratio did help distinguish compressive neuropathies from other systemic processes associated with diffuse nerve enlargement (eg, diabetes and polyneuropathy).

Subsequently, another study examined nerve vascularity in 137 patients afflicted with ulnar neuropathy at the elbow and determined that increased intraneural vascularization visualized by ultrasonography was indicative of axonal damage. [118]

Using high-resolution ultrasonography, Chiou et al found that the mean value of the area of the ulnar nerve at the level of the medial epicondyle in symptomatic patients was significantly larger than that of the control group and that of the unaffected, contralateral side. [119] They concluded that if the area of the ulnar nerve was greater than 0.075 cm2, at the level of the medial epicondyle, the patient probably had cubital tunnel syndrome.

An area in which ultrasonography may be particularly useful is evaluation of traumatic peripheral nerve injuries. In one study, 20 fresh cadaver arms were disarticulated, and the median, ulnar, or radial nerves were randomly transected in zero, one, or two locations per arm. [120] Sham incisions were performed throughout the extremity. The peripheral nerves were then systematically scanned by ultrasonographers who were blinded to the sites of transection.

The investigators found that high-resolution ultrasonography was able to identify transected nerves with 89% sensitivity and 95% specificity. [120] The diagnostic accuracy improved throughout the study: With the first 10 arms, the ultrasonographer correctly identified the transection in 77% of cases, whereas with the final 10 arms, the accuracy was 100%.

These findings suggest that the experience of the ultrasonographer has a vital effect on the diagnostic utility of ultrasonography in peripheral nerve injury. Thus, ultrasonography may be useful in determining the prognosis for nerve injury when an experienced ultrasonographer is available to distinguish between partial and complete injury, in localizing a nerve transection for possible surgical repair, or in both. [120, 121]

A further consideration is the comparison of the localizations derived from both sonographic and electrophysiological methods. Simon et al compared the lesion localization obtained by careful short-segment neurophysiological inching studies with that obtained by ultrasonographic methods. [122] For the larger segment across the entire elbow, the overall drop in conduction velocity correlated well with the maximum cross-sectional area (CSA) and maximal degree of hypoechoic fraction. However, on the short segments in patients whose lesion was apparently at the medical epicondyle as judged by neurophysiological methods, the maximal songraphic abnormalities were detected both slightly proximally and slightly distally to the medial epicondyle. It was concluded, therefore, that the ultrasonographic images may be detecting secondary changes adjacent to the major site of damage.

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Magnetic Resonance Imaging

MRI is being increasingly used in the evaluation of peripheral neuropathies, including ulnar neuropathy. [123] In most patients, history, physical examination, and electrophysiologic (EP) testing are sufficient to make the diagnosis of ulnar neuropathy, and MRI is not necessary. However, there may be a subgroup of patients with inconclusive findings on the standard evaluation in whom MRI may be beneficial. [124]

On MRI, normal nerves appear as smooth, round, or ovoid structures that are isointense to surrounding muscles on T1-weighted sequences. There is often a rim of hyperintense signal on T1. On T2-weighted images, the nerve is normally isointense to slightly hyperintense with respect to surrounding muscle. Normal nerves do not enhance after administration of gadolinium.

Possible changes that could be seen in neuropathies include increased signal intensity within the nerve on T2-weighted sequences. On MRI, increased signal intensity is a better indicator of ulnar nerve entrapment than enlargement of the nerve is.

Neurogenic muscle edema can be seen as early as 24-48 hours after denervation, and short T1 inversion recovery (STIR) sequences are particularly sensitive for that. This is to be contrasted with EP testing, in which changes after denervation are not seen for 1-3 weeks. After months of denervation, fatty muscle atrophy is seen. Changes in the surrounding structures that may be related to the neuropathy in question, such as osteoarthritis, synovitis, or tumors, can be seen with MRI as well. [125]

Several small studies have attempted to address the use of MRI in the diagnostic evaluation of ulnar neuropathy. Vucic et al identified 52 patients who met clinical criteria for ulnar neuropathy on the basis of either sensory symptoms or motor weakness in the distribution of the ulnar nerve; all underwent EP testing. [126] In 63%, the EP studies were diagnostic of an ulnar neuropathy at a specific location, commonly at the elbow. In 37%, the studies were nonlocalizing according to American Association of Electrodiagnostic Medicine criteria.

All 52 patients subsequently underwent MRI scanning as well, which revealed abnormalities in 90%. [126] Of those patients who had diagnostic EP studies, 94% had an abnormal MRI; of those who had nondiagnostic EP studies, 84% had an abnormal MRI. The authors concluded that MRI was “more sensitive” than neurophysiologic testing and that the sensitivity of MRI did not change, regardless of the EP results.

A study by Andreisek et al assessed 51 patients with clinically evident neuropathies in the radial, median, or ulnar nerve who were referred to their center for MRI scans of an upper extremity. [127] The aim of this study was to assess the impact of the MRI results on clinical decision making and patient management.

Andreisek et al found only a weak-to-moderate correlation between MRI results and clinical findings—not surprisingly, given that clinical findings imply physiologic dysfunction of the nerves, whereas MRI findings can evaluate nerve morphology alone. [127] The greatest use of MRI in this study seemed to be in cases where the cause of the symptoms was unclear; in this situation, MRI reportedly identified the symptom etiology in 93% of cases. This resulted in a moderate-to-major impact on treatment in 84% of the patients in this subgroup.

These seemingly positive results notwithstanding, some caveats remain. First, criteria for diagnosing neuropathy on MRI scans are not well defined. Second, the clinical significance of certain MRI findings has been questioned. Husarik et al performed MRI elbow scans in 60 asymptomatic patients and found that 60% had increased ulnar-nerve signal intensity without concomitant changes in their medial or radial nerves. This study suggests that increased signal intensity should not be the sole criterion in evaluation for possible ulnar neuropathy. [128]

Britz et al examined the use of MRI with a STIR sequence to diagnose cubital tunnel syndrome. [129] They studied 31 elbows with documented ulnar nerve entrapment and found increased signal intensity in the ulnar nerve in 97% of cases and enlargement of the ulnar nerve in 75%.

An additional development in MRI technology is diffusion-tensor imaging. [130] This has heretofore been used mainly to image central myelin tracts, but it is clearly applicable to peripheral myelin as well. As with central myelin, quantitative measures of MRI parameters, including fractional anisotropy (FA), can be obtained. Qualitative FA maps of nerve tracts allow observers to detect peripheral neuropathy with a sensitivity of 80% and a specificity of 83%, which are high enough to make them quite useful.

The role of MRI in the evaluation of ulnar and other peripheral neuropathies continues to evolve. At this point, it is reasonable to conclude that MRI may be a useful adjunct in select cases, either when a specific compressive lesion (eg, a mass) is suspected or when a patient with the clinical syndrome of ulnar neuropathy has nondiagnostic EP tests. To improve diagnostic accuracy, further research is required to develop standardized criteria for making the diagnosis of ulnar neuropathy on MRI. [127, 128, 129, 131]

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Electromyography and Nerve Conduction Studies

Electromyography (EMG) and nerve conduction studies are indicated to confirm the area of entrapment, document the extent of the pathology, and detect or rule out the possibility of double-crush syndrome. [132, 133, 134, 135] In recent entrapments of the ulnar nerve, motor and sensory conduction velocities are more useful, whereas in chronic neuropathies, conduction velocities and EMG are useful because EMG is capable of showing axonal degeneration.

EMG is not essential when the diagnosis of cubital tunnel syndrome is obvious on clinical examination; a false test result can be misleading and hinder rather than aid diagnosis. However, it is important to perform EMG when the diagnosis of cubital tunnel syndrome is unclear or when it is necessary to determine the efficacy of conservative treatment. [136]

Basic sensory and motor nerve parameters measured in nerve conduction studies include latency, amplitude, and conduction velocity. Electrodes (metallic reusable or pregelled disposable tape) are placed over the main belly of the active muscle (eg, the abductor digiti quinti or the first dorsal interosseous muscle) [109] and the tendon of the fifth or first digit. The ulnar nerve is stimulated at the wrist and above and below the elbow; this helps localize the site of involvement.

Short-segment stimulation (also known as the inching technique), in which the nerve is stimulated over 1- to 2-cm intervals, can increase the sensitivity of the procedure and may improve localization by helping the examiner judge whether a blockage is infracondylar (ie, near the cubital tunnel) or higher (ie, near the ulnar or epicondylar groove, the location associated with tardy ulnar palsy). (See the image below.)

Inching technique used to isolate conduction block Inching technique used to isolate conduction block in left ulnar nerve. Note significant amplitude drop at 305 mm, which correlates with position 2 cm above medial epicondyle. This is example of supracondylar block. Image courtesy of A S Lorenzo, MD.

Findings are considered to be positive for cubital tunnel syndrome when the motor conduction velocity across the elbow is less than 50 m/s or when the difference between the motor conduction velocity across the elbow and that below the elbow exceeds 10 m/s.

If the point of maximum conduction delay and drop in amplitude of the compound muscle action potential (CMAP) is at or just proximal to the medial epicondyle, compression of the ulnar nerve is probably at the level of the epicondylar groove. If the point of maximum conduction delay and drop in CMAP amplitude is 2 cm distal to the medial epicondyle, compression is probably in the cubital tunnel. Unfortunately, false-positive results are obtained in 15% of cases.

It should be kept in mind that in any given case, it is impossible to know the exact course the ulnar nerve follows. Considerable anatomic variation exists from person to person, and even controlling the angle of the elbow does not determine exactly where the nerve is running beneath the skin. Thus, the examiner does not know precisely where the nerve is being stimulated. The takeoff point of the impulse may not be exactly under the stimulator.

A good percentage of experienced electromyographers believe that in many if not most cases, the best that can be done is to establish whether a blockage exists at the elbow, and often, even that cannot be accomplished with certainty. The relevant anatomic issues have been discussed more fully by Campbell. [41]

Reservations aside, the reader is invited to try the inching technique and make an individual assessment of its potential utility in his or her own situation. This might include the following steps:

  • After performing the inching technique, report to the prospective surgeon where you think the blockage might be with respect to anatomic landmarks
  • Make it clear that this is a tentative assessment (ie, done to the best of your ability but not to be taken as definite)
  • Ask the surgeon to tell you where the blockage actually seemed to be after surgery was performed
  • Keep track of your own findings compared with surgical findings, and draw your own conclusions about how accurate the inching method is in your own hands

Even if the inching technique does not yield the exact localization of the lesion, the attempt to use it may be helpful in and of itself insofar as it makes the clinician more conscious of the anatomy.

Martin-Gruber anastomosis

The anatomic variant known as Martin-Gruber anastomosis is seen during routine nerve conduction studies and can pose a diagnostic dilemma if not identified as such. It is an anomalous pattern of innervation occurring between the median and ulnar nerves in the forearm. [137]

In a Martin-Gruber anastomosis, a crossover of axons from the anterior interosseous nerve (the exclusively motor branch of the median nerve) to the ulnar nerve in the forearm usually occurs. In such cases, no sensory fibers are involved in the crossover. However, in a small minority of cases, the crossover can occur from the main median trunk (in which case some sensory nerve fibers may cross over as well).

The Martin-Gruber anomaly occurs in 10-30% of individuals, and 60-70% of those affected show the anomaly bilaterally. In some families, an autosomal dominant inheritance is possible, though a gene controlling this occurrence has not been identified.

The fibers involved are from the C8/T1 nerve roots. Three patterns of Martin-Gruber anastomosis are commonly recognized, as follows (see the image below):

  • Type I (second most common pattern) - The hypothenar muscles are involved
  • Type II (most common pattern) - The crossover fibers innervate the first dorsal interosseous muscle
  • Type III (least common pattern) - The thenar muscles, typically the adductor pollicis and the flexor pollicis brevis rather than the abductor pollicis brevis, are involved; sometimes other muscles, including forearm muscles such as the flexor digitorum superficialis and the flexor digitorum profundus, are involved as well
    Normal median and ulnar patterns are compared with Normal median and ulnar patterns are compared with those of 3 commonly recognized types of Martin-Gruber anomaly.

In a patient who does not have a Martin-Gruber anastomosis, stimulating the median nerve at the wrist produces a CMAP amplitude at the thenar eminence (eg, abductor pollicis brevis) that is essentially the same size as the thenar CMAP produced by elbow stimulation. (The CMAP produced by wrist stimulation could be a bit larger because stimulating further away from the ultimate target muscle gives a little more temporal dispersion of the signal.)

In a patient who does have the anomaly, however, the wrist response is smaller because many axons from the median nerve have crossed already. Contributions from now median-innervated ulnar intrinsic hand muscles falsely increase the elbow response.

The converse is true with ulnar nerve stimulation during recording over the hypothenar eminence (abductor digiti quinti) or the first digital interosseous muscle; median nerve fibers are innervating ulnar muscles in the hand, and the elbow response is smaller (see the images below). This could be mistaken for a conduction block. Accordingly, a Martin-Gruber anastomosis should be excluded before an ulnar conduction block is diagnosed.

First 3 traces correspond to ulnar compound muscle First 3 traces correspond to ulnar compound muscle action potential (CMAP) amplitude during recording at abductor digiti quinti (ADQ) and stimulating at wrist, below elbow, and above elbow, respectively. Fourth trace corresponds to stimulation of median nerve at elbow during recording at ADQ. Although CMAP amplitude is reduced markedly above elbow, this is compensated for by adding response seen after stimulation of median nerve; this represents Martin-Gruber anastomosis.
First 3 traces correspond to stimulation of ulnar First 3 traces correspond to stimulation of ulnar nerve during recording at first dorsal interosseous (FDI) muscle at wrist, below elbow, and above elbow, respectively. Fourth trace corresponds to stimulation of median nerve at elbow during recording at FDI muscle; this represents Martin-Gruber anastomosis.

These relations can be visualized even more clearly by considering the characteristic EMG patterns with respect to the corresponding anatomy (see the image below).

In those with Martin-Gruber anomaly who have no ot In those with Martin-Gruber anomaly who have no other significant neuropathy or nerve compression, stimulation of specific nerves at different sites yields differing results. With median nerve, stimulation at elbow yields larger compound muscle action potential (CMAP) at hypothenar muscles, first dorsal interosseous (FDI) muscle, or thenar muscles (or combination thereof) than does stimulation at wrist. With ulnar nerve, stimulation at wrist yields larger CMAP at hypothenar muscles, FDI muscle, or thenar muscles (or combination thereof) than does stimulation at elbow. In this context, "larger" and "smaller" generally refer to amplitude differences ≥1.0 mV.

The distinctions between the three major types of the Martin-Gruber anastomosis, the tests performed to confirm them, and the possible areas of clinical confusion are summarized in the Table below.

Table. Types of Martin-Gruber Anastomosis (Open Table in a new window)

Type Anatomy Most Characteristic Finding Confirmation Additional Verification Potential Clinical Confusion
I Crossover fibers innervate hypothenar muscles Ulnar stimulation at wrist* produces larger hypothenar CMAP than stimulation at elbow Stimulation of median nerve at elbow† produces response at hypothenar muscles Hypothenar CMAP from ulnar stimulation at wrist is equal to hypothenar CMAP from ulnar stimulation at elbow plus hypothenar CMAP from median stimulation at elbow Smaller response from proximal stimulation could be mistaken for conduction block
II Crossover fibers innervate FDI muscle Ulnar stimulation at wrist produces larger FDI CMAP than stimulation at elbow Stimulation of median nerve at elbow produces response at FDI FDI CMAP from ulnar stimulation at wrist is equal to FDI CMAP from ulnar stimulation at elbow plus FDI CMAP from median stimulation at elbow Usually none, because FDI muscle is not usually recording site; if it is used, conduction block could be suspected, as in type I
III Crossover fibers innervate thenar muscles (typically ADP and FPB) Elbow stimulation of median nerve produces greater thenar response than wrist stimulation Ulnar stimulation produces thenar CMAP with initial positive deflection; it is higher with wrist stimulation than with elbow stimulation For thenar CMAP amplitudes, median elbow stimulation amp is equal to median wrist stimulation amplitude plus ulnar wrist stimulation amplitude minus ulnar elbow stimulation amplitude Can complicate median nerve studies, especially when carpal tunnel syndrome is involved
ADP—adductor pollicis; CMAP—compound motor (or muscle) action potential; FDI—first dorsal interosseous; FPB—flexor pollicis brevis.



*Ulnar stimulation at wrist yields larger CMAP at hypothenar muscles, FDI, or thenar muscles (or sometimes combination of these) than does stimulation at elbow.



†Median stimulation at the elbow yields larger CMAP at hypothenar muscles, FDI, or thenar muscles (or sometimes combination of these) than does stimulation at wrist.



Note: “Larger” and “smaller” generally mean amplitude difference ≥1.0 mV.



Two potentially important diagnostic implications are associated with this Martin-Gruber anomaly.

First, in cases of carpal tunnel syndrome (ie, median mononeuropathy at the wrist), the larger median CMAP amplitude at the elbow has an initial positive (ie, downward) deflection, which is not seen at the wrist. The explanation is that the median nerve axons are traveling slower through the carpal tunnel, so that the median-innervated ulnar hand muscles conduct first, leading to a volume-conducted response that is manifested by a positive deflection.

If carpal tunnel syndrome is suspected clinically, the chance of a false-negative result on nerve conduction testing is still about 8-10%. Given that the anomaly exists 15-31% of the time, a chance still exists of diagnosing carpal tunnel syndrome electrically.

Second, in suspected cases of ulnar neuropathy at the elbow or forearm, a reduced-to-absent response would be expected proximally with sparing of the wrist responses, provided that no diffuse severe axon loss has occurred.

To disprove a true ulnar neuropathy, stimulation of the median nerve at the elbow would lead to a wrist response that, when added to the response achieved by stimulating the ulnar nerve at the elbow, would equal a difference of less than 20-25% between elbow and wrist, which is acceptable as normal temporal dispersion. Stimulation of the median nerve at the wrist should lead to a small response; this would represent contributions from ulnar-derived muscles in the thenar eminence. [138, 139, 140, 141]

Riche-Cannieu anastomosis

Another anomaly that can complicate diagnostic studies is the Riche-Cannieu anastomosis (see the image below).

Riche-Cannieu anastomosis is communication between Riche-Cannieu anastomosis is communication between recurrent branch of median nerve and deep branch of ulnar nerve in hand. Although it is present in 77% of hands, it yields highly variable degrees of detectable physiologic difference; in many hands, it contributes little and does not affect diagnostic findings at all. Most common effect is probably to give ulnar innervation to some muscles usually innervated by median nerve, median innervation to muscles usually innervated by ulnar nerve, or both. Most extreme version is so-called all-ulnar hand (very rare). Two examples of confusion this might cause are as follows. (1) Median lesion could cause denervation in typically ulnar muscle, such as adductor digiti minimi (adductor digiti quinti) or first dorsal interosseous muscle. (2) Ulnar lesion could cause denervation in typically median muscle, such as flexor pollicis brevis or abductor pollicis brevis.
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Histologic Studies

Nerve enlargement in cases of entrapment typically occurs proximal to the point of compression.

Nerve compression leads to a cascade of edema, demyelination, inflammation, axonal loss, fibrosis, and remyelination with subsequent thickening of the perineurium and endothelium

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