Pitfalls in the electrodiagnostic studies of sacral plexopathies

This retrospective review characterizes the electrodiagnostic (EDX) features and etiologies of sacral plexopathies (SPs) and discusses difficulties in their identification. The EDX findings of 171 clinically suspected SPs were reviewed using the following criteria: reduced/absent sensory nerve action potentials (SNAPs) of the sural or superficial peroneal nerve, denervation of plexus-innervated muscles, and the absence of paraspinal denervation. Sixty cases localized unequivocally to the sacral plexus. The majority were cancer-related, followed by traumatic, idiopathic, and iatrogenic causes. Final diagnoses in the remaining 111 cases were indeterminate. Lesions localized to either the plexus or L4-5, S1 roots in 52 cases, the plexus or sciatic nerve in 32 cases, and were equally compatible with an SP, sciatic neuropathy, or radiculopathy in 27 cases. Findings in the EDX evaluation of SPs are often complex and difficult to localize to a specific site due to multiple complicating factors. Frequently, SPs cannot be diagnosed definitively by EDX assessment alone.