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|Year : 2012 | Volume
| Issue : 1 | Page : 36-39
The pattern of muscle involvement in ulnar neuropathy at the elbow
Dariush Eliaspour1, Leyla Sedighipour1, Mohammad Reza Hedayati-Moghaddam2, Seyed Mansoor Rayegani1, Mohammad Hassan Bahrami1, Reza Salman Roghani1
1 Physical Medicine and Rehabilitation Research Center, Shohada Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
2 Iranian Academic Center for Education, Culture and Research (ACECR), Mashhad, Iran
|Date of Submission||29-Sep-2011|
|Date of Decision||18-Oct-2011|
|Date of Acceptance||28-Dec-2011|
|Date of Web Publication||7-Mar-2012|
Department of Physical Medicine and Rehabilitation, Shohadaye-e-tajrish Hospital, Shahid Beheshti University of Medical Sciences, Tehran
Objective: To determine the pattern of muscle involvement in patients with ulnar neuropathy at the elbow. Materials and Methods: This study evaluated all patients referred for upper limb electrodiagnostic study (EDX) during 2007-2011 and included. patients with clinical signs and symptoms of ulnar neuropathy at the elbow. All patients had nerve conduction studies (NCS) for ulnar neuropathy. Needle electromyography (EMG) of four ulnar innervated muscles, flexor carpi ulnaris (FCU), flexor digitrom profoundus (FDP), first dorsal interosseous (FDI) and abductor digiti minimi (ADM)) was evaluated. Results: During the study period 34 (23 males and 11 females) patients were diagnosed with ulnar neuropathy at the elbow and three of them had bilateral involvement. Muscle involvement by EMG was as follows: FDI: 91.9%, ADM: 91.3%, FCU: 64.9% and FDP: 56.8%. Conclusion: In this study, EMG abnormalities of nerve damage were presented more commonly in the FCU muscle than in the FDP in patients with ulnar nerve lesion at the elbow.
Keywords: Needle electromyography, nerve conduction study, ulnar neuropathy
|How to cite this article:|
Eliaspour D, Sedighipour L, Hedayati-Moghaddam MR, Rayegani SM, Bahrami MH, Roghani RS. The pattern of muscle involvement in ulnar neuropathy at the elbow. Neurol India 2012;60:36-9
|How to cite this URL:|
Eliaspour D, Sedighipour L, Hedayati-Moghaddam MR, Rayegani SM, Bahrami MH, Roghani RS. The pattern of muscle involvement in ulnar neuropathy at the elbow. Neurol India [serial online] 2012 [cited 2014 Sep 20];60:36-9. Available from: http://www.neurologyindia.com/text.asp?2012/60/1/36/93586
| » Introduction|| |
Ulnar nerve entrapment at the elbow is the second most common focal peripheral neuropathy in upper limbs. [ 1],,, Patients usually complain of paresthesia or hypoesthesia in the volar aspect of the fourth and fifth fingers. In more severe cases weakness and atrophy might be detected in intrinsic hand muscles. , Several factors make the ulnar nerve vulnerable at the elbow. Cubital tunnel syndrome is one of the most common types of ulnar neuropathy at the elbow.  The nerve can be compressed beneath the flexor carpi ulnaris (FCU) muscle aponeurosis or arcuate ligament. However, in most of the cases, the etiology remains idiopathic. , The best and most precise diagnostic method for detecting the nerve injury is by electrodiagnostic studies. ,, The common abnormality observed in nerve conduction studies (NCS) is motor nerve conduction velocity (NCV) across the elbow less than 49 m/s 2 , or the presence of conduction block across the elbow segment.  Electromyography (EMG) may show evidence of neurogenic patterns in the ulnar-innervated muscles. , The FCU muscle may be spared in some cases of ulnar neuropathy at the elbow, because the branch of ulnar nerve innervating this muscle might arise proximal to the medial epicondyle , There are other explanations that can justify this phenomenon more rationally. According to the intraneural topogra[phy theory, the nerve fibers supplying the FCU muscle are located medially and are thus better protected from external trauma; while nerve fibers of hand intrinsic muscles and sensory fibers are located laterally and thus are more prone to injury. ,,, An alternative explanation is axoplasmic flow abnormalities. According to this theory externally applied pressure impairs axoplasmic flow which leads to a dying-back phenomenon preferentially in the longest fibers. , Based on these observations, some authors believe that electrodiagnostic evaluation of the FDP muscle is more sensitive than evaluation of the FCU muscle in detecting ulnar neuropathy at the elbow. , Addressing this controversy we designed the present study to describe the pattern of muscle involvement by needle EMG in ulnar neuropathy at the elbow.
| » Materials and Methods|| |
This study was conducted in Shohada University Hospital, in Tehran, Iran and had the approval of the Shahid Beheshti University of Medical Sciences and Epilepsy Association Ethics Committees as per the guidelines by the Declaration of Helsinki.
All consecutive patients referred to the electrodiagnotic laboratory between 2007 and 2010 were evaluated. Screening and physical examination were performed by a physiatrist. All patients with clinical symptoms and signs of ulnar neuropathy at the elbow including paraesthesia or hypoesthesia in the medial aspect of the hand or fourth and fifth fingers and/or positive tinel sign were included in the study. The patients included in the study had a standardized clinical and electrodiagnostic evaluation. The criteria for the diagnosis of ulnar neuropathy at the elbow included:1) slowing of conduction velocity in the ulnar nerve across the elbow to less than 50m/s or 2) conduction block across the elbow, more than 30% and 3) neurogenic EMG in ulnar-innervated muscles (1).
Individuals with brachial plexopathy, polyneuropathy or cervical radiculopathy (diagnosed by clinical signs, symptoms and electrodiagnostic study) were excluded from the study. Patients with contraindications for needle EMG were also excluded.
Electrodiagnostic (EDX) tests were performed by a two-channel synergy electrodiagnostic instrument (Medelec™ Synergy T-EP). Standard EDX techniques , were used for median, ulnar and radial nerves' motor conduction studies across the wrist, forearm (median and ulnar) and elbow (ulnar). Sensory conduction studies were also performed for the same nerves and also for medial and lateral ante-brachial nerves under the same conditions and standards. Surface electrodes were used for NCS. Standard electromyography techniques and muscle selection (1) were followed for all the appropriate muscles of the upper extremity including the muscles of interest, flexor carpi ulnaris (FCU), flexor digitrom profoundus (FDP), first dorsal interoseous (FDI) and abductor digiti minimi (ADM), for mapping the the ulnar nerve injury and ruling out differential diagnoses. The criteria for neurogenic EMG included: membrane instability; defined as fibrillation potentials and/or positive sharp waves, polyphasic (>4 phases) and/or long-duration motor unit action potentials (MUAPs) (≥13 ms), reduced recruitment and/or reduction in interference pattern. (1) Concomitant ulnar neuropathy at the wrist was excluded by standard physical examination and history-taking and EDX criteria; no significant compound muscle action potential (CMAP) latency difference was recorded from ADM and FDI (1).
Variables were described using standard descriptive statistics. Categorical variables were summarized into counts and percentages. Statistical analysis was done with the SPSS-14 software package.
| » Results|| |
During the period of the study, 2000 patients were referred to our electrodiagnostic laboratory for upper limb EDX examination. Of those, 34 patients were diagnosed with ulnar neuropathy at the elbow. Demographic features, clinical characteristics, and etiology of the patients are presented in [Table 1]. Electrodiagnostic findings are given in [Table 2],[Table 3] and [Table 4]. All patients with slowed NCV across the elbow had EMG abnormalities in some or all ulnar-innervated muscles. Muscle involvement by EMG was as follows: FDI: 91.9%, ADM: 91.3%, FCU: 64.9% and FDP: 56.8%. EMG abnormalities were more common in FCU than FDP.
|Table 2: Sensory nerve action potential (SNAP) abnormalities in ulnar neuropathy at the elbow (number of cases shown in columns)|
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|Table 3: CMAP abnormalities in ulnar neuropathy at the elbow (number of cases shown in columns)|
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| » Discussion|| |
Electrodiagnostic evaluation of ulnar neuropathy is a challenge for electromyographers. ,, There are very few published studies evaluating needle EMG findings and pattern of muscle involvement in ulnar neuropathy at the elbow. ,4], In our study, all patients with slowed NCV across the elbow had EMG abnormalities in some or all ulnar-innervated muscles which might be related to the duration of the symptoms, more than six months. Most of the earlier studies have focused on conduction studies rather than needle EMG of FCU. ,, Normal ulnar compound action potential (CMAP) amplitude was defined in some studies as a good prognostic indicator for recovery.  Even though we did not have long-term follow-up in our patients, 86% of them had abnormal ulnar CMAP which could be a sign of poor recovery. In our study, the most common etiology of ulnar neuropathy was idiopathic just as what is indicated in most studies. ,
Needle EMG of ulnar-innervated muscles is essential to determine the presence and severity of axonal loss. Especially in severe and longstanding cases, NCS may not exactly localize the site of lesion. , In the present study, needle EMG of the FDI and ADM muscles revealed the same abnormalities. In the study by Azrieli et al., no significant difference in the sensitivity of these two muscles for the diagnosis of ulnar neuropathy at the elbow was found.  In another study, the frequency of motor involvement in ulnar neuropathy at the elbow was the highest in FDI, less in ADM, still less in FDP, and the least in FCU.  Some authors believe that needle EMG of the FDP muscle is more sensitive than FCU for the diagnosis of ulnar neuropathy at the elbow (1). Intraneural topography and axoplasmic flow abnormalities are two explanations for sparing of FCU in unlar neuropathy at the elbow (1). We found that the FCU muscle had slightly more EMG abnormalities than the FDP muscle. This observation was not in agreement with the theory of FCU muscle sparing in ulnar neuropathy at the elbow. ,, In a study by Campbell, FCU involvement was correlated with the severity of the neuropathy and with whether compression was retroepicondylar or at the humerulnar aponeurosis.  Similar to previous studies, , we found that the FDI muscle had the most common EMG abnormalities compared to other muscles and could still serve as the best muscle for the diagnosis of ulnar neuropathy. Nevertheless, this muscle can also be involved in ulnar nerve lesions at the wrist, so its evaluation cannot localize the lesion site. ,
In the present study, we concluded that needle examination of the FCU muscle could have the same value or even more value than examination of the FDP for the diagnosis of ulnar neuropathy at the elbow . Our study had some limitations. As we did not aim to determine the sensitivity and the specificity of EMG findings of ulnar-innervated muscles, further studies with predetermined sample size are suggested to investigate the sensitivity and specificity of needle EMG of each ulnar-innervated muscle according to a gold standard test.
| » Acknowledgment|| |
We acknowledge Dr.Masoomeh Bayat for her great contribution in this article and Katayoon Bidad for her precious help.
| » References|| |
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[Table 1], [Table 2], [Table 3], [Table 4]