[A case of a postmedian sternotomy C8 plexopathy localized with electrodiagnostic tests].

A postmedian sternotomy plexopathy is a C8 plexopathy following an operation that requires a median sternotomy, in which the C8 anterior primary ramus is injured. Since the clinical picture of a C8 plexopathy is quite similar to an ulnar neuropathy, electrodiagnostic tests are crucial for localizing the lesion and confirming the diagnosis. This is the first published report in Japan that shows the clinical picture of a postmedian sternotomy C8 plexopathy and the utility of electrophysiological tests to diagnose this disease. A 54 year-old man developed numbness in the right ring and little fingers just after an operation through a median sternotomy to treat an aortic dissection. His symptoms did not improve and he was reevaluated 11 months after the operation. Neurological examinations revealed a weakness of the right ulnar-innervated hand muscles, and tingling dysesthesia of the ring and little fingers. In electrodiagnostic tests, the ulnar SNAP was severely depressed on the affected side, and in addition the amplitude of the median SNAP over the ring finger (Med-D4) was also reduced by more than half of that observed in his healthy side (62% side-to-side difference). In our investigation of 26 control subjects, the side-to-side difference of the Med-D4 SNAP amplitude did not exceed 50% for any subject. Needle electromyography revealed profuse denervation activities in the FCU, ADM and EPB, and moderately reduced recruitment and giant motor unit potentials in the EI. The postmedian sternotomy plexopathy had been long described, but its precise localization using modern electrodiagnostic techniques has been presented only recently in the literature. Our results are largely the same as those found in previous reports, which show the predominant involvement of the ulnar sensory and motor fibers and electromyographic changes in C8-radial muscles (EPB and EI). Furthermore, the antidromic SNAP of Med-D4 was significantly reduced in amplitude on the affected side, and supported the diagnosis of the C8 plexopathy. The Med-D4 method is the only method that can document a nonulnar C8 involvement solely by NCS. Whereas the potential role of the Med-D4 method has been suggested in this condition, this is the first report that actually showed its utility.