Needle electromyography at 1 month predicts paralysis of elbow flexion at 3 months in obstetric brachial plexus lesions.

Aim Treatment decisions in obstetric brachial plexus lesions are often based on clinical paralysis of elbow flexion at 3 months of age, when electromyography (EMG) is misleading because motor unit potentials (MUPs) occur in clinically paralytic muscles. We investigated whether EMG at 1 week or 1 month identifies infants with flexion paralysis at 3 months, allowing early referral. Method Forty-eight infants (27 females, 21 males) were prospectively studied. The presence or absence of flexion paralysis at around 1 week (median 9d; range 5-17d), 1 month (median 31d; range 24-53d), and 3 months of age (median 87d; range 77-106d) was noted for clinical (shoulder external rotation, elbow flexion, extension, and supination) and EMG parameters (denervation activity, MUPs and polyphasic MUPs in the deltoid, biceps, and triceps muscles). Results At 1 month, the absence of biceps MUPs had a sensitivity of 95% for later flexion paralysis, and absence of deltoid MUPs had a sensitivity of 100% for flexion paralysis; the false-positive rates for the same findings were 21% and 33% respectively. EMG at 3 months was highly misleading as MUPs were seen in 19 of 20 clinically paralytic biceps muscles. Interpretation EMG at 1 month can identify severe cases of flexion paralysis for early referral EMG of the biceps at 3 months is highly misleading; the discrepancy between the EMG and clinical testing may be due to abnormal axonal branching and aberrant central motor control. [ABSTRACT FROM AUTHOR]