Bilateral Musculocutaneous Nerve Palsy From Strength Training
Samuel O. Matz, MD; Gregg Nibbelink, ATC
THE PHYSICIAN AND SPORTSMEDICINE - VOL 32 - NO. 3 - MARCH 2004
In Brief: Musculocutaneous nerve palsy resulting from strenuous weight training is a rare condition characterized by biceps atrophy or weakness. It usually affects the dominant side, but the authors describe an 18-year-old football player who developed the condition bilaterally after weight lifting—a presentation not found in the literature. Clinicians should keep the diagnosis in mind for active patients who perform repetitive biceps curls. When other neurologic conditions have been clinically ruled out, electrodiagnostic testing can confirm the diagnosis. Musculocutaneous nerve palsy typically resolves when weight training routines are modified to reduce intensity and biceps curls are eliminated for at least 3 months.
Strength training is a popular pastime for many active patients, but strenuous lifting may have unintended consequences. Many college athletes do strength training as a manditory, organized part of their off-season conditioning. Musculocutaneous nerve palsy in weight training may result from excessive workouts with biceps curls.
The cause appears to be either nerve impingement because of hypertrophy of the brachioradialis muscle or a traction injury to the nerve from repetitive biceps curls.
Bilateral musculocutaneous nerve palsy following strenuous weight training is rare and usually affects only the dominant side. We report a case of bilateral involvement after strength training, which, as far as we know, has yet to be reported.
In this case of a college football player, primarily the motor branch of the musculocutaneous nerve was involved, but cases involving only the sensory branch of the lateral cutaneous nerve have been reported. The diagnosis of bilateral musculocutaneous nerve involvement was confirmed with electrodiagnostic testing after cervical radiculopathy, brachial neuritis, intrinsic muscle disease, and focal motor neuropathy were ruled out. Consistent with other reported cases of this syndrome, the patient's symptoms completely resolved when the offending activity, biceps curls, was removed from his weight training routine.
History. An 18-year-old right-handed college football player reported to the team athletic trainer with bilateral biceps weakness and bilateral biceps atrophy without pain. The student was promptly referred to the team physician. He said he first noticed the problem after weight training. Incidentally, while on the way to shower, he noticed a loss of prominence of biceps bulk while striking a muscular pose in a mirror. The patient could not recall any specific injury. Retrospectively, he described a 3-week history of poor performance on biceps curls and chin-ups. He also stated that he may have experienced some numbness on the radial aspect of the right distal forearm, but this sensation was transient and resolved. At least 3 weeks elapsed between the time he noticed symptoms and when he saw the team physician.
The freshman had completed an uneventful fall season as a linebacker and reported no specific head, neck, or shoulder trauma. He began an aggressive off-season strength training program in early December. The daily program included biceps curls, bench presses, incline press lat pull-downs, seated rows, and power cleans. Typical high-intensity workouts required three to four sets of 10 to 12 repetitions with 90- to 120-second rests between sets.
Exam findings. Physical exam revealed bilaterally flaccid biceps. The patient was unable to "make a muscle," and he had weakness on biceps testing at 4/5 flexion and supination (movement possible against some resistance by the examiner). His shoulder motion was full. Biceps reflex could not be elicited, but triceps and brachioradialis reflexes were present. No sensory loss to light touch was noted, and two-point discrimination and cervical motion were normal. He reported no cervical tenderness. Rotator cuff strength and muscle strength testing of the brachioradialis, deltoid, and triceps were normal. His cervical-spine radiographs were normal, but magnetic resonance imaging showed a small disk herniation on the left at C5-6. No neural effacement was seen.
Differential diagnosis. Diagnostic considerations at this point were cervical origins, a primary muscle disease, brachial neuritis (ie, Parsonage-Turner syndrome), and bilateral musculocutaneous neuropathy from weight training.
Further tests. The patient was then referred for electrodiagnostic testing 4 to 6 weeks after the onset of initial symptoms, and the musulocutaneous nerve response was absent bilaterally. Needle electromyography was performed bilaterally in multiple arm muscles. The only serious abnormality was spontaneous activity and decreased recruitment in the biceps muscles bilaterally. The axillary nerve and the sensory branch of the musculocutaneous nerve (ie, the lateral antebrachial cutaneous nerve) tested normally. No other definitive abnormalities were noted. The patient's serum creatine kinase level was normal on one occasion and mildly elevated on another (230 U/L; normal for men is 55 to 170 U/L). The mild elevation initially was attributed to high-intensity weight lifting. After neurologic and orthopedic evaluations, physicians agreed to treat the athlete conservatively.
Treatment. A fitness program was outlined that eliminated biceps work. An aerobic workout routine and lower-extremity weight training program were recommended. The patient noticed slow improvement of biceps tone and strength over 3 to 4 months. Repeat testing 4 months later showed normal nerve conductions bilaterally in the musculocutaneous nerves.
The patient exhibited no further symptoms consistent with a primary muscle disease or neurologic disorder. He recovered full muscle strength and gradually resumed less vigorous biceps workouts, but he was advised to allow recovery days after doing biceps curls. He was cautioned that he could be at risk of developing this syndrome if he continued with his previous intensity on biceps curls. We recommended that he pursue a more generalized weight training program that alternated upper-extremity and lower-extremity work. He was able to play football his sophomore year and was treated for an unrelated ankle sprain in his junior year of college.
Musculocutaneous neuropathy from weight lifting is rare but not unknown.1 In one report,2 the dominant arms of three male patients who performed repetitive biceps curls were involved. All three patients were affected by biceps weakness, and all symptoms resolved in 3 months. Other isolated cases of unilateral musculocutaneous neuropathy have been noted in the literature.3-8
To our knowledge, a bilateral case of musculocutaneous nerve palsy has not been specifically reported as a result of weight training. A report of a bilateral lesion subsequent to a crush injury from a collapsed wooden deck is noted.5 Review of the literature reveals two postulated syndromes involving the musculocutaneous nerve.8 One is a lesion of the musculocutaneous nerve before its division into the lateral cutaneous nerve that causes a mixed motor and sensory syndrome. The other is a lesion of the sensory portion only that causes loss of sensation but no motor loss.8
Our patient had a more proximal lesion, and his history and exam revealed motor loss but no sensory loss. Electrodiagnostic testing showed only motor involvement. Only by retrospection did our patient recall some transient numbness on the lateral distal forearm that is sometimes seen with the proximal lesion.
Aggressive weight lifting with biceps curls may lead to musculocutaneous nerve palsy that usually affects the dominant side but can be bilateral. Several theories for this condition have been set forth. The most often cited cause is impingement of the musculocutaneous nerve from coracobrachialis muscle hypertrophy.9 Additionally, a traction mechanism on the nerve from biceps curls as it is anchored by the coracobrachialis muscle has been implicated.9 Our patient's case was notable for the bilaterally symmetric presentation without any specific trauma. As in previous unilateral cases associated with weight lifting, our patient's symptoms resolved with activity restriction for 3 to 4 months—the typical interval when weight training is limited and biceps curls are discontinued.
Dr Matz is an orthopedic surgeon at The Advanced Centers for Orthopedic Surgery and Sports Medicine in Westminster, Maryland. Mr Nibbelink is the head athletic trainer at McDaniel College in Westminster, Maryland. Address correspondence to Samuel O. Matz, MD, The Advanced Centers for Orthopedic Surgery and Sports Medicine, 1 Village Sq, Westminster, MD 21157; e-mail to: [email protected].
Disclosure information: Dr Matz and Mr Nibbelink disclose no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.