June 1996 EMG Case-of-the-Month

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Angelica Kennedy
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1 June 1996 EMG Case-of-the-Month This case is no longer available for CME credit. Cases prepared by: Ian MacLean, MD; Daniel Dumitru, MD; Lawrence R. Robinson, MD HISTORY Six weeks ago a 28-year-old woman was riding her bicycle and was struck by a car, sustaining a left acromioclavicular separation. She also has numbness over the dorsal left hand and thumb. Seven days she also noticed gradually worsening weakening of the left hand, during a long bike ride. Prior to continuing, please develop a differential diagnosis and list each diagnosis in order of likelihood. Is there any additional information from the clinical history that might be helpful in clarifying your differential list or changing its order of priority? ADDITIONAL HISTORY There are no previous such episodes, and no pertinent personal or family past history. On what details of the physical examination do you think you should focus at this point? PHYSICAL EXAMINATION Spurling sign is negative. There is weakness of the left first dorsal interosseus and adductor pollicis muscles; strength is otherwise normal. The pronator teres and biceps stretch reflexes are mildly diminished on the left, the brachioradialis and triceps are symmetric. There is sensory loss over the lateral forearm, dorsal hand and thumb, and dorsal index finger on the left, poorly circumscribed. At this point, review your differential diagnosis and revise as appropriate. Formulate your approach to the electrodiagnostic evaluation based on your differential diagnosis. Copyright 1996 AAPM&R Page 1 of 6

2 ELECTROPHYSOLOGIC DATA ELECTROMYOGRAPHY n = normal incr = increased decr = decreased 0 = absent 1+ = minimal 4+ = maximal crd = complex repetive discharge fasc = fasciculation potential myk = myokymic discharge myt = myotonic discharge nmt = neuromyotonic discharge R/L MUSCLE INSERTION SPONTAN VOLUNTARY activ p wave fib other recrt amp dur poly effort L paraspinal (C2-T1) n n n n - L infraspinatus n n n n n L deltoid n n n n - L biceps n n n n - L brachioradialis n n n n n L serratus anterior n n n n - L pronator teres n n n n - L ext carp rad n n n n n L pect maj (clavic) n n n n - L latissimus dorsi n n n n - L flex carp rad n n n n - L flex carp uln n n n n n L triceps (long) n n n n - L ext carp uln n n n n n L pect maj (stern) n n n n - L abd dig quinti n 6mV 1 incr n - L 1st dors interos decr 9mV 1 incr n - L oppon poll n n n n n SENSORY NERVE CONDUCTION nr = no response NERVE LATENCY AMPLITUDE ( µv) CONDUC VEL(m/s) R L Norm R L Norm R L Norm radial wrist to thumb (<2.9) (>3) median wrist to thumb (<3.0) - 45 (>14) ulnar wrist to digit (<2.9) (>10) Copyright 1996 AAPM&R Page 2 of 6

3 NERVE MOTOR NERVE CONDUCTION nr = no response LATENCY (ms) AMPLITUDE (mv) CONDUC VEL (m/s) R L Norm R L Norm R L Norm ulnar wrist to (<3.7) (>5) - - hypothenar - BE to - hypothenar (>51) AE to - hypothenar (>58) Are there any additional electrophysiologic data that you feel might provide further information which would be helpful to you in clarifying the diagnoses under consideration? (Remember, the collection of unnecessary data is both costly and uncomfortable for the patient.) ELECTROMYOGRAPHY n = normal incr = increased decr = decreased 0 = absent 1+ = minimal 4+ = maximal crd = complex repetive discharge fasc = fasciculation potential myk = myokymic discharge myt = myotonic discharge nmt = neuromyotonic discharge R/L MUSCLE INSERTION SPONTAN VOLUNTARY activ p wave fib other recrt amp dur poly effort L 3rd dorsal interos decr 10mV 1 incr n - L 4th dorsal interos decr 8mV 1 incr n - MOTOR NERVE CONDUCTION nr = no response NERVE LATENCY (ms) AMPLITUDE (mv) CONDUC VEL (m/s) R L Norm R L Norm R L Norm ulnar wrist to 1st dors Copyright 1996 AAPM&R Page 3 of 6

4 F-WAVE # = number of stimuli P = persistence CD = chronodispersion F:M = ratio of average F-wave amplitude to M-wave amplitude R/L NERVE # LATENCY (ms) min mean max CD (ms) P (%) F:M (%) L ulnar wrist to hypothenar normal values <6 >60 <4 Formulate your final impression based both on the clinical and on the electrophysiologic evaluations. List the most likely diagnosis first followed by other possibilities that are not excluded by the data. Eliminate those diagnoses not supported by the data. DIFFERENTIAL DIAGNOSIS The onset of numbness in the left upper limb in close association with a traumatic injury of the head and left shoulder six weeks ago leaves little doubt that peripheral nerve has been injured. The numbness is in the distribution of the C6 dermatome or the upper trunk/lateral cord of the brachial plexus. Weakness of the left hand developing while cycling seven days ago draws immediate attention to the possibility of ulnar compression in the region of Guyon's canal. Consideration must also be given to a possible connection between the hand weakness and the head/shoulder injury, but any connection would have to explain why the distribution of new symptoms is anatomically separate (C8 myotome-lower trunk/medial cord of plexus vs. C6/upper trunk), and why a lesion in this location has not caused new sensory symptoms involving the medial side of the hand. A third, much less likely possibility for the hand weakness is focal ulnar neuropathy at the elbow. The additional history offers nothing that would alter these considerations. The physical examination adds new data that help to define the problem. The presence of weakness in the left 1st dorsal interosseus suggests a distal lesion of the ulnar nerve, since there is no weakness in more proximal muscles. The absence of weakness in the abductor digiti quinti is consistent with a lesion distal to the branch to that muscle. The impairment of the left brachioradialis and pronator teres reflexes is consistent with either a C6 or an upper trunk lesion. The left biceps reflex (some contribution from C5) is spared, often the case with C6 lesions but not with lesions of the upper trunk. Also, the sensory deficit is more typical of abnormality involving the C6 root than the upper trunk. Thus, a careful clinical examination appears to have defined two local sites of peripheral nerve injury: the C6 nerve root (at least the dorsal root) and the deep motor branch of the ulnar nerve. Copyright 1996 AAPM&R Page 4 of 6

5 ANALYSIS OF THE ELECTROPHYSIOLOGIC DATA The needle electrode examination needs to be designed not only to explore the areas of suspected pathology, but also to be certain that subtle plexopathy is not overlooked. All the major motor nerves that branch from the plexus were evaluated, but positive waves and fibrillation potentials were confined to the C6 myotome. They were not found in the paraspinal muscles, but this does not exclude the possibility of radiculopathy. The chronology of these findings is consistent with the six-week period since the bicycle accident. No positive waves or fibrillation potentials were found in the intrinsic muscles of the hand, but reduced recruitment (reflecting a decrease in the number of functioning motor units) was detected in the distribution of the deep motor branch of the ulnar nerve. The absence of spontaneous activity is consistent with the seven days since the onset of weakness of the hand. Reduced recruitment in the 4th dorsal interosseus but not in the abductor digiti quinti places the lesion at the deep motor branch close to its origin. Unsuspected findings on the needle electrode examination included abnormally large motor unit potentials (increased amplitude and duration) in all the ulnar-innervated intrinsic muscles of the hand. These reflect collateral reinnervation of previously denervated muscle fibers and are much older than the 7-day history of weakness. These findings together with a lack of sensory symptoms and signs identify an older lesion in the region of Guyon's canal. Since no symptoms preceded the onset of weakness, the nerve damage must have occurred very gradually, presumably due to external pressure during prolonged cycling. Amplitudes of sensory nerve action potentials recorded from the left thumb following stimulation of the radial and median nerves were well within normal limits despite hypesthesia over the dorsum of the thumb. This places the pathology proximal to the dorsal root ganglion and confirms the site of a lesion involving the C6 nerve root that was suspected during the clinical and needle electrode examinations. Since the study to determine if left ulnar sensory nerve fibers are damaged at Guyon's canal produced normal values, the same study was done on the right to look for side-to-side differences. None was present. Conduction in the deep motor branch of the left ulnar nerve was abnormal. (A right/left comparison of the difference in the latencies recorded from the abductor digiti quinti and 1st dorsal interosseous muscles should not be more than 0.5ms.) Also, the amplitude of the compound muscle action potential recorded from the 1st dorsal interosseous on the left was markedly reduced as compared to the right side. Conduction values for the more proximal portions of the left ulnar nerve (including F-waves) were normal. Ulnar conduction across the plexus and elbow were evaluated to be certain that there was not more than one site of nerve pathology. IMPRESSION 1. Acute left C6 radiculopathy. The clinical and electrophysiologic data are consistent with the onset occurring six weeks ago at the time of the patient's bicycle accident. Copyright 1996 AAPM&R Page 5 of 6

6 2. Acute compression neuropathy of the left ulnar nerve just distal to Guyon's canal involving the deep motor branch of the ulnar nerve. All data are consistent with this condition occurring during the patient's 26-mile bicycle ride seven days ago. 3. There is also an old or chronic, focal compression neuropathy of the left ulnar nerve in the region of Guyon's canal involving the deep motor branch more than the branch to the abductor digiti quinti. The distal sensory fibers are spared. This occurred in the past and is likely related to frequent bicycle riding. 4. Since a compression neuropathy of the left ulnar nerve in the region of Guyon's canal is present presumably as a result of cycling, a similar condition on the right side should be considered as a possibility either currently (asymptomatically) or in the future. Preventive measures should be directed to both the right and left sides. COMMENTS This patient presents with two clinical problems that can be rather confusing, because of the tendency to link both problems to the initial traumatic injury. A careful clinical evaluation properly separates and identifies the two separate conditions. In this case, the electrophysiologic evaluation is most useful in confirming the clinical impression both anatomically and chronologically. It also revealed an unexpected, asymptomatic, chronic compression neuropathy in the region of Guyon's canal. This discovery adds emphasis to preventive measures regarding cycling that are to become part of the patient's treatment program. The chronology of the acute ulnar nerve lesion could be reliably documented by finding positive waves in any one muscle innervated by the deep motor branch of the ulnar nerve within the next few days. However, the clinical history already provides a strong indication that the injury occurred seven days ago. Finally, since there is an asymptomatic ulnar neuropathy on the left, presumably associated with cycling, a similar lesion should be anticipated on the right and appropriate measures taken for prevention of further injury to that side as well. Electrodiagnostic studies to look for such a lesion on the right were not undertaken. BIBLIOGRAPHY 1. Brandstater ME, Fullerton M: Sensory nerve conduction studies in cervical root lesions. Can j Neurol Sci 10:152, Olney RK, Wilbourn AJ: Ulnar nerve conduction study of the first dorsal interosseous muscle. Arch Phys Med Rehabil 66:16-18, Shea JD, McClain EJ: Ulnar-nerve compression syndromes at and below the wrist. J Bone Joint Surg 51A: , Wilbourn AJ, Aminoff MJ: AAEE Minimonograph #32: The electrophysiologic examination in patients with radiculopathies. Muscle Nerve 11: , 1988 Copyright 1996 AAPM&R Page 6 of 6

Assessment of the Brachial Plexus EMG Course CNSF Halifax Fraser Moore, Canadian Society of Clinical Neurophysiology McGill University

Assessment of the Brachial Plexus EMG Course CNSF Halifax 2018 Fraser Moore, Canadian Society of Clinical Neurophysiology McGill University Angela Scott, Association of Electromyography Technologists of