Martin Gruber Anastomosis

Peripheral nerve myelination begins at approximately the 15th week of gestation and continues through 3 to 5 yr of age. Therefore, for children younger than the age of 5 yr, special tables are required to evaluate NCS data. In term infants, the latency and conduction velocity values are approximately half those recorded in adults, and premature infants have even slower conduction velocities; at the beginning of the third trimester, velocities are one-third of those measured in term infants.

NCS parameters are fairly stable from age 5 yr through 40 yr, and then there is a tendency towards slower latencies and velocities with lower amplitudes. In the healthy older

Martin Gruber Anastomosis
Fig. 2. The effect of warming. (A) At ambient temperature, the median sensory response is of longer latency, higher amplitude and longer duration than the same response (B) after the hand has been warmed.

population older than age 60 yr, upper extremity NCS latencies are relatively unchanged when compared with younger adult populations. Between the ages of 60 to 90 yr, median, radial, and ulnar sensory amplitudes fall slightly. Lower extremity latencies tend to increase and velocities tend to decrease compared with younger adults. Lower extremity motor and sensory amplitudes decrease throughout middle age, and the trend continues in the elderly. The thought that sural sensory responses may be absent in the elderly is widely circulated, but one study found recordable sural potentials in 98% of individuals older than age 60 yr, and superficial peroneal sensory responses in 90% of the same group.

Studies on the effect of age on NCS parameters consistently show that amplitude is more affected by this process than is velocity. Possible explanations for the changes in NCS with aging include "normal" axon loss caused by neuronal senescence, higher prevalence of asymptomatic, generalized neuropathy, increased lower extremity edema, and a higher prevalence of subclinical entrapment neuropathies.

8.3. Height

As opposed to the effects of aging, increasing height influences latencies and velocities more than amplitude. The effect is particularly evident in the lower extremities, and, in general, increasing height results in longer distal latencies, slower conduction velocities, and slightly reduced amplitude. The effect of height may not cause collected data to deviate from commonly used normal ranges except for very tall or very short individuals. Unusually fast velocities and latencies are not usually given consideration because the values are considered supernormal rather than pathological, however, in very short persons, latencies at the upper end of commonly used "normal" ranges may be pathological if not adjusted for height.

Similarly, very tall people may seem to have mild generalized slowing of NCS parameters that does not reflect demyelination or other pathology. It is easy to see that, at the extremes of height, mild neuropathic processes could be overlooked or mistakenly identified.

One theory purported to explain the effect of height on NCS is that, in taller people, the axons are more tapered and smaller in diameter in the distal segments than in people of common height. Another proposed explanation is that the distal segments are relatively cooler despite attempts at adequate warming.

9. ANATOMIC VARIATIONS 9.1. Martin-Gruber Anastomosis

The Martin-Gruber anastomosis (MGA) is a common anatomic variant of peripheral nerve pathways in the forearm. It involves primarily motor fibers that cross over from the median nerve in the proximal forearm to the ulnar nerve at the wrist. Although the MGA is identifiable in up to 30% of people, many instances of MGA do not affect the interpretation of the NCS data and, thus, are not identified. The MGA can be inherited in an autosomal dominant pattern and can be unilateral or bilateral. In the MGA, the course of the ulnar fibers from the plexus is altered, such that a portion of the ulnar fibers descends with the median nerve to the elbow. These fibers branch off the median nerve in the forearm (often via fibers from the anterior interosseous nerve) to join the ulnar nerve proximal to the wrist. The intrinsic hand muscles are innervated by the "usual" nerve (unlike the "all-ulnar hand"); it is only the pathway that particular ulnar fibers take to get to the wrist that is anomalous. There are three types of MGA to consider, but combinations of the types may occur and generally make the anomaly easier to recognize.

Type I: Crossover fibers innervate the ADQ. When the crossover involves the ADQ, the median studies appear normal, but ulnar stimulation at the wrist (recording from ADQ) produces a much higher-amplitude waveform than on stimulation below the elbow. The drop in amplitude may exceed the 10 to 20% reduction that is expected over this distance because of normal phase cancellation and temporal dispersion. The type I MGA can be confirmed by recording from ADQ while stimulating the median nerve at the elbow and demonstrating an initially negative (upward) waveform that is similar in amplitude to the "drop" seen between the distal and proximal ulnar stimulation sites. If the MGA goes unrecognized in this situation, conduction block of the ulnar nerve in the forearm may be erroneously diagnosed. The clinical situation and EMG results may alert the diagnostician to investigate the possibility of MGA rather than conduction block, but, in cases in which demyelinating neuropathy is clinically suspected, the possibility of MGA may be overlooked.

Type II: Crossover fibers innervate the first dorsal interosseous (FDI). This is the most common type of MGA. Ulnar NCS recording from the FDI can be used to evaluate lesions of the deep palmar branch or to investigate ulnar neuropathy at the elbow. The pattern of amplitude change is similar to that seen in type I and can mimic a conduction block of the ulnar nerve in the forearm. As with type I, type II MGA is proven by stimulating the median nerve at the wrist and elbow, and noting a higher amplitude response from the proximal site while still recording from FDI. During routine median motor studies, recording from APB, a type II MGA is often suggested by a slightly enlarged or altered median CMAP appearance with elbow stimulation when compared with the CMAP obtained at the wrist. Because NCS recording from FDI are not routinely performed in most labs, type II MGA is often detected in the setting of carpal tunnel syndrome (CTS) (see next paragraph).

In cases of CTS with prolonged distal motor Type III: Crossover fibers innervate thenar eminence muscles that have ulnar innervation (adductor pollicis and/or flexor pollicis bre-vis-deep head). Type III MGA is recognized during median motor NCS by an increase in amplitude at the proximal site. Submaximal wrist stimulation or co-stimulation of the ulnar nerve from the antecubital fossa produces a similar pattern and should be initially investigated. The MGA is confirmed by stimulating the ulnar nerve at the wrist (still recording from the thenar eminence over the abductor pollicis brevis) and then at the elbow. In persons with and without MGA, wrist stimulation produces a waveform with an initial positive deflection caused by volume conduction from ulnar innervated muscles thenar eminence. In individuals without MGA, stimulation of the ulnar nerve at the elbow, produces a waveform of similar appearance without much reduction of amplitude, but, in those with MGA, stimulation at the elbow results in a much lower amplitude than at the wrist, often with altered morphology.

In cases of CTS with prolonged distal motor latencies, type II and type III MGA are easier to detect, because median stimulation at the elbow produces a positive deflection before the CMAP, which was not observed with wrist stimulation. The delay through the carpal tunnel prevents the abductor pollicis brevis muscle from depolarizing before the muscles innervated by the crossover fibers. The initial volume-conducted response from the crossover muscles results in the "positive dip." If the onset latency is marked at the beginning of the "positive dip," the median forearm conduction velocity will be erroneously fast and usually nonphysiological (>80 m/s). An accurate velocity cannot be measured because the takeoff for the "true" median CMAP is lost in the positive deflection. This pattern is so distinctive that the diagnosis of CTS plus MGA can be made by inspection of the median waveforms without determining the type of MGA. Distal and proximal ulnar nerve stimulation recording from the thenar eminence and FDI, as described in this section, will differentiate between type II and type III MGA (Fig. 3). Ulnar studies recording from ADQ are unaffected in this situation.

In the setting of ulnar neuropathy at the elbow or proximal median neuropathy, serious errors in EMG interpretation are easily made if the MGA is unrecognized during NCS. Sparing of the certain ulnar muscles innervated by crossover fibers in ulnar neuropathy at the elbow produces patterns that may mimic a lesion of the deep palmar branch. Similarly, a lesion of the proximal median nerve affecting crossover fibers could produce a pattern suggesting C8 radiculopathy on EMG, because abnormalities may be identified in both median-and ulnar-innervated hand muscles.

9.2. Accessory Peroneal Branch to Extensor Digitorum Brevis

The extensor digitorum brevis (EDB), the recording location for peroneal motor NCS, is usually exclusively innervated by the deep branch of the peroneal nerve. In 13 to 22% of people, a branch of the superficial peroneal nerve traveling behind the lateral malleolus innervates the lateral portion of the EDB. The anomalous innervation is recognized when proximal peroneal stimulation produces a higher amplitude CMAP than that obtained by stimulation at the ankle. Submaximal stimulation at the ankle or co-stimulation of the tibial nerve in the popliteal fossa may cause a similar pattern, and should be considered initially. The presence of an accessory peroneal branch is confirmed by low-intensity stimulation behind the lateral malleolus and demonstrating a CMAP with an initial negative deflection. Rarely, the EDB is completely supplied by the accessory branch.

Martin Gruber Anastomosis

Fig. 3. Type II Martin-Gruber anastomosis (MGA) to first dorsal interosseous (FDI) with carpal tunnel syndrome. In (A), the median nerve is stimulated at the wrist and a response with a prolonged latency is recorded. Median nerve stimulation at the elbow generates a slightly higher amplitude waveform preceded by a positive deflection (B). Stimulation of the ulnar nerve at the wrist (C) and elbow (D) recording over the abductor pollicis brevis muscle does not show a significant difference in amplitude, excluding a type III MGA. In (E-H), the recording electrodes are moved over the FDI. The median nerve is stimulated at the wrist (E) and elbow (F), demonstrating the type II MGA. Then, the ulnar nerve is stimulated at the wrist (G) and elbow (H), demonstrating the drop in amplitude expected from this type of crossover.

Fig. 3. Type II Martin-Gruber anastomosis (MGA) to first dorsal interosseous (FDI) with carpal tunnel syndrome. In (A), the median nerve is stimulated at the wrist and a response with a prolonged latency is recorded. Median nerve stimulation at the elbow generates a slightly higher amplitude waveform preceded by a positive deflection (B). Stimulation of the ulnar nerve at the wrist (C) and elbow (D) recording over the abductor pollicis brevis muscle does not show a significant difference in amplitude, excluding a type III MGA. In (E-H), the recording electrodes are moved over the FDI. The median nerve is stimulated at the wrist (E) and elbow (F), demonstrating the type II MGA. Then, the ulnar nerve is stimulated at the wrist (G) and elbow (H), demonstrating the drop in amplitude expected from this type of crossover.

REVIEW QUESTIONS

1. All of the following interventions may reduce stimulus artifact EXCEPT:

A. Increasing the distance between stimulating and recording electrodes.

B. Cleaning the skin with acetone.

C. Reducing the sensitivity on the display.

D. Rotating the anode of the stimulator while leaving the cathode stationary.

E. Placing the ground electrode between the stimulating and recording electrodes.

2. In sensory NCS, signal-to-noise ratio can be improved by all of the following EXCEPT:

A. Placement of subdermal monopolar needle electrodes for recording.

B. Increasing the interelectrode difference beyond 3 to 4 cm.

C. Averaging.

Martin Gruber Anastomosis Ncs

D. Cleaning the skin with alcohol.

E. Decreasing the distance between the stimulating and recording electrodes.

3. All of the following can cause a "positive dip" on routine NCS EXCEPT:

A. Co-stimulation.

B. Improper recording electrode placement.

E. Submaximal stimulation.

4. Virtual cathode commonly occurs during:

A. Stimulation at intensity above supramaximal.

B. Submaximal stimulation.

D. Axonal neuropathy.

E. Improper recording electrode placement.

5. Virtual cathode can result in all of the following EXCEPT:

A. An erroneously short latency.

B. An erroneously fast conduction velocity.

C. Significantly higher amplitudes.

D. Loss of sensitivity to entrapment neuropathy distal to the stimulation point.

E. More patient discomfort.

6. If the signal-to-noise ratio is 1:4, how many times would the potential need to be averaged to produce a signal-to-noise ratio of 2:1?

7. During NCS, inadequate warming of a limb will have the most marked effect on:

A. Amplitude.

B. Distal latency.

C. Proximal conduction velocity.

D. Decrement.

E. Duration.

A. Some muscles in the thenar eminence that are typically innervated by the median nerve are innervated by the ulnar nerve.

B. The proximal median amplitude is always higher than the distal median amplitude.

C. A pseudoconduction block of the ulnar nerve in the forearm may occur.

D. The sensory potential recording from digit two has contributions from the median and ulnar nerves.

E. Individuals who have this variant may have relative protection from median neuropathy at the wrist.

9. In accessory peroneal nerve branch to the EDB:

A. Responses may mimic a conduction block in the calf.

B. Responses may mimic a conduction block across the fibular head.

C. Anamolous innervation is by stimulating behind the lateral malleolus.

D. Anamolous innervation is when the bulk of the EDB is reduced.

E. The accessory branch involves only sensory fibers.

10. After recording of the motor CMAP, if the stimulator is not "turned around" with the cathode where the anode had been, the F-waves will:

A. Be absent because of anodal block.

B. Have a longer latency.

C. Will show more chronodispersion.

D. Have a shorter latency.

E. Be reduced in amplitude.

REVIEW ANSWERS

1. The correct answer is C. Reducing the sensitivity on the display does not change the degree of stimulus artifact relative to the recorded potential of interest.

2. The correct answer is B. Increasing the interelectrode difference beyond 3 to 4 cm does not result in higher amplitude signals. Reducing the distance between the stimulator and recording electrodes will result in higher amplitudes.

3. The correct answer is C. When recording over the thenar eminence and stimulating the median nerve at the elbow, a positive dip is not usually seen unless there is concomitant CTS slowing down the action potentials as they enter the hand.

4. The correct answer is A. Virtual cathode occurs when stimulation intensity is sufficient to depolarize the nerve distal to the location of the stimulating cathode.

5. The correct answer is C. Virtual cathode is unlikely to have an appreciable effect on the amplitude of the response. The most noticeable effect is a shorter latency, resulting in faster conduction velocities and erroneously fast velocities across entrapment point immediately distal to the stimulation point.

6. The correct answer is A. The square root of the number of stimuli is the factor that improves the signal-to-noise ratio. In this case, the square root of 64 is eight times the given signal-to-noise ratio of 1:4 = 8:4 = 2:1.

7. The correct answer is B. Inadequate warming of a limb usually produces a marked effect on distal latency because the distal parts of the limb tend to be the coldest. Expected lesser effects include increased amplitude, decrease proximal conduction velocity, decreased decrement (if present), and increased duration of the response.

8. The correct answer is C. An MGA involving the ADQ would be expected to produce a drop in amplitude when comparing the distal site with the proximal site. This will have an appearance of conduction block in the forearm and not across the elbow.

9. The correct answer is C. The accessory branch of the peroneal nerve to the EDB is confirmed by stimulating behind the lateral malleolus. This anatomic variant is suspected when the amplitude at the below fibular head site is higher than the amplitude recorded at the ankle. Therefore, it does not mimic a conduction block.

10. The correct answer is B. When F-waves are recorded with the stimulator in position for routine motor studies, there is a risk that some potential F-waves will be blocked under the anode. However, F-waves are typically recordable with the cathode distal to the anode, although they have a slightly longer latency than if the cathode and anode positions had been reversed.

REFERENCES

1. Kincaid JC, Brasher A, Markand ON. The influence of the reference electrode on CMAP configuration. Muscle Nerve 1993;16:392-396.

2. Hodgkin AL, Katz B. The effect of temperature on the electrical activity of the giant axon of the squid. J Physiol (Lond) 1949;109:240-249.

3. Rutkove SB. The effects of temperature in neuromuscular electrophysiology. Muscle Nerve 2001;24:867-882.

4. Rivner MH, Swift TR, Malik K. Influence of age and height on nerve conduction. Muscle Nerve 2001;24:1134-1141.

5. Falco FJE, Hennessey WJ, Braddom RL, Goldberg G. Standardized nerve conduction studies in the upper limb of the healthy elderly. Am J Phys Med Rehabil 1992;71:263-271.

6. Falco FJE, Hennessey WJ, Goldberg G, Braddom RL. Standardized nerve conduction studies in the lower limb of the healthy elderly. Am J Phys Med Rehabil 1994;73:168-174.

7. Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders. ButterworthHeinemann, Boston, MA, 1998.

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Responses

  • Martin B
    What generates anastomosis?
    4 years ago
  • juanita
    How does martin gruber affect EMG tests?
    4 years ago
  • columbus
    How to diagnose martin gruber anastomosis ncv studies?
    4 years ago
  • zula
    What is cure for MartinGruber anastomosis?
    3 years ago
  • Amina Trevisano
    What muscle is most commonly innervated by a martingruber anastamosis?
    3 years ago
  • lea
    How does martin Gruiber affect CTS?
    3 years ago
  • marie schultz
    WHAT TYPE OF CARPUL TUNNELL SURGERY IS NEEDED FOR MARTIN GRUBERS ANASTAMOSIS?
    3 years ago
  • Rosario
    How does a martin gruber occur?
    3 years ago
  • gundobad
    How does a person get martin gruber nerve problem?
    3 years ago
  • ALMAZ
    How does martin gruber anastomosis effect carpal tunnel?
    3 years ago
  • louie
    What is Marvin gruber syndrome?
    2 years ago
  • yolanda
    When to suspect martin gruber anastomosis in emg?
    2 years ago
  • boris
    How to pick up for martin gruber on nerve conduction studies?
    2 years ago
  • roderic
    How does a martin gruber anastomosis present on nerve conduction?
    1 year ago
  • kathryn
    Does Martin Gruber Anastomosis hurt and Symptoms?
    11 months ago
  • j
    What is martingruber anatomosis?
    7 months ago
  • FINDLAY
    HOW DOES A MartinGruber anastomosis AFFECT A PERSON?
    7 months ago
  • Adelbert
    Can you get martingruber anastomosis in your ankle?
    7 months ago
  • manu
    What symptoms does a person have with martin gruber anastomosis?
    2 months ago

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