The natural history of long thoracic and spinal accessory neuropathies.

A cohort of 106 patients with electrodiagnostically confirmed long thoracic neuropathy (50 patients) or spinal accessory neuropathy (56 patients) seen at the Mayo Clinic over a 22-year period were retrospectively studied to better understand the natural history of these disorders and to determine the role of electrodiagnostic testing in predicting prognosis. Mean follow-up was 48 and 50 months, respectively. Good functional recovery was generally observed regardless of the results of electrodiagnostic studies, but improvement in the amplitude of the spinal accessory compound muscle action potential on serial nerve conduction studies tended to predict a good outcome. No electrodiagnostic findings correlated with poor outcome. Traumatic neuropathies generally did worse than neuropathies of other causes. In spinal accessory neuropathies, involvement of the dominant limb, scapular winging, and impaired arm elevation were associated with a poor outcome. Our data suggest that, contrary to other focal neuropathies, the electrodiagnostic findings do not predict functional outcome in these neuropathies.