THE ABSENCE OF BRACHIAL-PLEXUS INJURY IN STROKE

Brachial plexus injury and proximal mononeuropathy have been reported as a potential complications in the hemiplegic shoulder after a stroke. The diagnosis of brachial plexus injury and proximal mononeuropathy in the hemiplegic extremity is complicated by the upper motor neuron findings on physical examination and by the diffusely abnormal electrodiagnostic test results frequently seen in hemiplegic limbs. This study investigated the incidence of brachial plexus injury and proximal mononeuropathy after a thromboembolic stroke. Hemiplegic patients (n = 50) underwent physical examination, needle electromyography of the hemiplegic extremities and nerve conduction studies across the brachial plexus within 4 months after a stroke. Combining the physical examination and electromyographic findings we were unable to make a diagnosis of brachial plexus injury or proximal mononeuropathy in any hemiplegic patient. Spontaneous electromyographic activity was observed in 68% of the arms and 70% of the legs examined on the hemiplegic side. The severity and incidence of spontaneous activity was evenly distributed in upper and lower trunk muscles. Mean central latencies across the lower brachial plexus were slightly delayed (12.5 +/- 2 v 11.6 +/- 2.2 ms, P < 0.01) compared with the contralateral normal limb, but in no case was the F wave unilaterally unelicitable. The mean hypothenar compound muscle action potential amplitude was diminished (7 +/- 2.7 v 9.2 +/- 4.1 mV, P < 0.01) in the hemiplegic hand compared with the normal side and the degree of amplitude loss inversely corresponded (r = -0.6, P < 0.01) to the amount of spontaneous electromyographic activity observed in the first dorsal interosseus muscle. There was no correlation between compound muscle action potential amplitude and muscle strength, and no individual patient had an absent or severely reduced compound muscle action potential amplitude, even when there was no volitional movement in the corresponding muscle (n = 16). There was a negative correlation (r = -0.8, P < 0.001) between spontaneous activity and muscle strength in the hemiplegic arm. A positive correlation (r = 0.5, P < 0.01) was observed between the number of days following stroke that needle examination was performed and the degree of spontaneous electromyographic activity observed. In the context of the literature we concluded that these findings probably reflect minimal motor axon degeneration secondary to the cortical lesion rather than any brachial plexus injury or proximal mononeuropathy with severe axonal loss or complete conduction block.