International Journal of Neuroscience, 2014; 124(7): 542546Copyright 2014 Informa Healthcare USA, Inc.ISSN: 0020-7454 print / 1543-5245 onlineDOI: 10.3109/00207454.2013.858336

CASE REPORT

Ulnar neuropathy with prominent proximal Martin-Gruberanastomosis

Ahmet Z. Burakgazi,1 Mary Russo,2 Elham Bayat,2 and Perry K. Richardson2

1Neuroscience Section, Department of Medicine, Virginia Tech Carilion School of Medicine, Roanoke, VA, USA;2Department of Neurology, George Washington University, Washington, DC, USA

Martin-Gruber anastomosis (MGA) is the most common nerve anastomosis in the upper extremities and itcrosses from the median nerve to the ulnar nerve. Proximal MGA is an under recognized anastomosis betweenthe ulnar and median nerves at or above the elbow and should not be missed during nerve conduction studies.We presented two patients with ulnar neuropathy mimicking findings including numbness and tingling of the 4thand 5th digits and mild weakness of intrinsic hand muscles. However, both cases had an apparently remarkableconduction block between the below- and above-elbow sites that was disproportionate to their clinical findings.To explain this discrepancy, a large MGA was detected with stimulation of the median nerve at the elbow. Thus,proximal MGA should be considered in ulnar neuropathy at the elbow when apparent conduction block or/anddiscrepancy between clinical and electrodiagnostic findings is found.

KEYWORDS: proximal Martin-Gruber anastomosis, ulnar neuropathy, nerve conduction studies

Ulnar neuropathy at the elbow is the second most com-mon mononeuropathy in electrodiagnostic laboratories,after carpal tunnel syndrome [13]. The clinical findingsinclude weakness of interossei muscles and decreasedsensation in the ulnar nerve distribution. The electrodi-agnostic findings include a presence of a significant dropin ulnar motor amplitude with above elbow stimulationalong with slowing of conduction velocity (CV) orabnormal temporal dispersion. However, a discrepancycan rarely be seen between clinical and electrodiagnosticfindings [1,3,4]. These discrepancies can be apparentconduction block (CB) without slowing of CV withabove elbow stimulation of the ulnar nerve, or apparentCB between below- and above-elbow stimulation ofthe ulnar nerve without consistent clinical findings [3,58]. Thus, if one detects a significant discrepancybetween the clinical and electrodiagnostic findings,an alternative explanation should be investigated[3,6,911].

Typical Martin-Gruber anastomosis (MGA) is acrossover between median and ulnar nerves in the fore-arm. Proximal MGA is an under recognized anastomo-sis between the ulnar and median nerves at or above the

Received 10 August 2013; revised 20 October 2013; accepted 20 October 2013

Correspondence: Ahmet Z. Burakgazi, MD, Carilion Clinic, 3 RiversideCircle, Roanoke, VA 24016, USA. E-mail: drburakgazi@yahoo.com

elbow and should not be missed during nerve conduc-tion studies (NCS) [9,10,12]. Its electrodiagnostic de-tectionmay bemisinterpreted as evidence of conductionblock when there may be none, and thus misinterpretedas evidence of ulnar neuropathy in a normal individual[9,10,13]. This may lead to inappropriate intervention.Herein, we present two cases of ulnar neuropathy withprominent MGA to emphasize the importance of proxi-mal MGA assessment in patients with ulnar neuropathywhen electrodiagnostic findings are not consistent withclinical findings [2,5,9,10].

Case Reports

Patient 1

A 60-year-old male with a history of diabetes presentedwith pain and numbness in the fingers, particularly thedigits 4th and 5th for two months, with nocturnal pares-thesia of the hand, more on the right side for severalmonths. The patient also described right hand weak-ness, difficulties in grasping and fine motor activities,and tenderness over the medial aspect of the elbow. Hedenied neck pain radiating to his upper extremity. How-ever, the numbness and pain in his forearm and ulnarside of the hand could radiate up to his shoulder.

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Ulnar Neuropathy with Prominent MGA 543

The physical examination showed his cranial nerveswere intact, 5/5 strength was in the shoulder girdle,proximal upper arms, and forearm muscles except for4/5 strength was in the interossei muscle (4/5) and ab-ductor pollicis brevis (APB) muscles; sensation to lighttouch, pin prick, vibration was intact except there was adecreased sensation on the ulnar side of the hands bilat-erally and at the tip of the first three fingers; deep tendonreflexes were intact; Babinski response was absent; andhis coordination and gait examination were within nor-mal limits.

Patient 2

A 45-year-old male with no significant past medical his-tory presented with right 4th and 5th digit numbnessfor 68 months. The patient did not have any remark-able weakness in his hands. He denied neck pain andhad mild tenderness over the medial aspect of the elbowthat radiated to the shoulder and hand.

The physical examination demonstrated that CNwere within normal limits; 5/5 strength in upper andlower limb muscles; sensation to light touch and pinprick was decreased on the ulnar side of the right hand;deep tendon reflexes were intact; Babinski response wasabsent; and his coordination and gait examination werewithin normal range.

Nerve conduction studies

TechniqueUlnar motor NCS were performed with disc electrodes.G1 was placed over the muscle belly of abductor digitiminimi (ADM) and first interossei muscles (FDI), G2was placed at the lateral base of fifth digit for ADM orat the base of second digit for FDI; and G0 was placedon the dorsum of hand, in between S1 and G1. The cur-rent was gradually increased to the point that the CMAPno longer increased in side in order to obtain supra-maximal stimulation. The elbow was in a flexed positionduring ulnar motor nerve stimulation. The ulnar nervewas stimulated at three points: S1: 68 cm proximal toG1 over the ulnar nerve at the wrist; S2: 46 cm distalto the ulnar groove (BG); and S3: 1012 cm proximalto the below elbow site of stimulation (AG). Using aninching technique with 2-cm increments, the amplitudechange was found to occur between 46 cm distal tothe medial epicondyle. Proximal MGA was suspected incases when a decrement in ulnar motor nerve amplitudewas >0.5% or >0.30.4 MV with AG stimulation com-pared with BG stimulation [2,3,9,10]. To confirm themedian to ulnar crossover, the disc electrodes were kepton the ulnar-innervated muscles and the median nervewas stimulated at the elbow, over the brachial pulse. If

there was a proximal MGA, a response upon stimula-tion of the median nerve at the elbow was detected. Thestimulation sites and a schematic depiction of proximalMGA is shown in Figure 1.

Figure 1. Depiction of proximal MGA. (Please see Figures 2and 3 for descriptions of A, B, C, D, F, G, H, 1, 2, 3, 4, 6, 7, 8.)FDI: First Dorsal Interosseus; APB: Abductor Pollicis Brevis.Med. Epic: Medial Epicondyle.

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544 A. Z. Burakgazi et al.

Patient 1NCS revealed absent right ulnar digital cutaneous sen-sory nerve action potentials (SNAPs), decreased ampli-tude of left ulnar sensory SNAP, and decreased ampli-tude of right median SNAP with delayed latency. Theright and left ulnar/first dorsal interosseous (FDI) motorNCS showed a decline in compound motor action po-tential (CMAP) amplitude (98% and 55%, respectively)across the elbow segment, with slowed CV. Then discelectrodes were kept on the FDI andmedian nerves werestimulated at the elbow. 4.7 mV and 8.7 mV CMAPamplitudes were obtained from ADM and FDI mus-cles with median nerve stimulation at the elbow, respec-tively (Figure 2A and 2B). The response and decrementwas attributed to a large proximal MGA. The right me-dian/thenar motor NCS showed mildly prolonged la-tency. The median nerve CMAP amplitude recordingfrom abductor pollicis brevis (ABP) was 11.2 mV withwrist stimulation and 9.3 mV with elbow stimulation.

Concentric needle electromyography of the right upperlimb showed chronic denervation in the FDI muscle.This patient was diagnosed with ulnar neuropathy andcarpal tunnel syndrome.

Patient 2Nerve conduction studies showed decreased amplitudeof the right ulnar sensory nerve action potential. Theright ulnar/FDI motor NCS showed a decline in CMAPamplitude (92%) across the elbow segment with normalconduction velocity. A 10.2 mV and 12.2 mV CMAPamplitude response was obtained from ADM and FDImuscles with median nerve stimulation at the elbow, re-spectively (Figure 3A and 3B). The response and decre-ment was attributed to a large proximal MGA. The me-dian nerve CMAP amplitude recording from APB was15.9 mV with wrist stimulation and 15.3 mV with elbowstimulation. Concentric needle electromyography of theright upper limb was within normal limits.

Figure 2. Demonstration of prominent MGA from ADM (Figure 2A) and from FDI (Figure 2B) muscles inPatient#1. (A): Ulnar nerve stimulation site at the wrist recording over ADM; (B): Ulnar nerve stimulation sitebelow the elbow recording over ADM; (C): Ulnar nerve stimulation site above the elbow recording over ADM;(D): Median nerve stimulation site at the elbow while recording over ADM; (E): Ulnar nerve stimulation siteat the wrist recording over FDI; (F): Ulnar nerve stimulation site below the elbow recording over FDI; (G):Ulnar nerve stimulation site above the elbow recording over FDI; (H): Median nerve stimulation site at theelbow while recording over FDI.

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Ulnar Neuropathy with Prominent MGA 545

Figure 3. Demonstration of prominent MGA from ADM (Figure 3A) and from FDI (Figure 3B) muscles inPatient#2. (1): Ulnar nerve stimulation site at the wrist recording over ADM; (2): Ulnar nerve stimulation sitebelow the elbow recording over ADM; (3): Ulnar nerve stimulation site above the elbow recording over ADM;(4): Median nerve stimulation site at the elbow while recording over ADM; (5): Ulnar nerve stimulation siteat the wrist recording over FDI; (6): Ulnar nerve stimulation site below the elbow recording over FDI; (7):Ulnar nerve stimulation site above the elbow recording over FDI; (8): Median nerve stimulation at the elbowwhile recording over FDI.

Discussion

MGA is the most common nerve anastomosis in theupper extremities and is seen around 15%30% ofnormal individuals [2,4,5,12]. The incidence of MGAfor normal individuals has been reported as 11%24%in various cadaveric studies [1315], and 15%39% inprevious nerve conduction reports [5,8,16]. MGA mayarise from the main trunk of the median nerve or fromone of its branches, particularly anterior interosseousnerve. The crossed over median nerve fibers mergewith the distal ulnar nerve to innervate ulnar nerveinnervated muscles [5,10,14].

There are four well-defined types of MGA [5] local-izing in forearm: (1) Type 1 is the most common type(approximately 90% of cases) and arises between an-terior interosseous and ulnar nerves, (2) Type 2 arisesbetween the median and ulnar nerve trunks, (3) Type

3 arises between branches innervating the flexor digito-rum profundus muscles, and (4) Type 4 is anastomicbranch from the median or anterior interosseous nervejoining the ulnar nerve at two different points[5,13,14].

Proximal MGA is an under-recognized anastomosisbetween ulnar and median nerves at or above the elbow[5,10,13]. An accompanying ulnar neuropathy can bedetected based on the clinical findings including weak-ness of intrinsic hand muscles and decreased sensationon the ulnar nerve distribution and the electrodiagnos-tic findings including slowing in conduction velocity andabnormal ulnar sensory nerve action potential response[5,10,11]. Marras et al. [10] reported a patient withproximal MGA mimicking ulnar neuropathy at the el-bow. Whitaker et al. [9] detected proximal MGA inthree patients over a period of 2 years. In our cases,the patients had ulnar neuropathy mimicking findingsincluding numbness and tingling of the 4th and 5th

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digits and mild weakness of intrinsic hand muscles.However, both cases had an apparently remarkable con-duction block between the below- and above-elbow sitesthat was disproportionate to their clinical findings. Itshould be considered that there is a potential for mis-interpretation with understimulation at the above site ofstimulation and overstimulation at the median nerve atthe elbow. Thus, stimulation should be increased gradu-ally and carefully to avoid this misinterpretation. To ex-plain this discrepancy, a large MGA was detected withstimulation of the median nerve at the elbow. This in-consistency was explained with the presence of a promi-nent proximal MGA.

In conclusion, proximal MGA should be consideredin ulnar neuropathy at the elbow when apparent con-duction block or/and discrepancy between clinical andelectrodiagnostic findings is found.

Declaration of Interest

The authors report no conflict of interest. The authorsalone are responsible for the content and writing of thispaper.

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