The breathing hand: obstetric brachial plexopathy reinnervation from thoracic roots?

It has been found that in cases of obstetric brachial plexopathy, injured phrenic nerve or C3/4/5 roots may sprout into the adjacent injured upper and middle trunks of the brachial plexus. This aberrant regeneration produces co-contraction of the diaphragm and proximal upper limb muscles. This phenomenon, referred to as respiratory synkinesis or "the breathing arm", may not be limited to the upper cervical roots. We present two cases, identified through electromyographic investigations, of respiratory synkinesis selectively affecting intrinsic hand muscles, and propose that upper thoracic roots and their intercostal nerves may also produce respiratory synkinesis, resulting in a "breathing hand." This novel brand of synkinesis indicates that obstetric brachial plexus neuropathies can have quite proximal nerve injury in all trunks. The findings in our patients may not be entirely unique. The time required to develop distal muscle synkinesis and the subtle nature of our findings may suggest that with time and the assistance of EMG the breathing hand may be more common. When considering brachial plexus surgery, the significance of respiratory synkinesis should not be overlooked as its presence indicates injury at a root or proximal trunk level and may come from either nerves destined for the diaphragm or for the intercostal muscles.