The role of somatosensory evoked potentials in the diagnosis of AIDS-associated myelopathy

Background: Although AIDS-associated vacuolar myelopathy is detected in >50 % of autopsy cases, it is often unrecognized during life. The clinical asse ssment is often difficult because of concurrent peripheral neuropathy and l ack of specific diagnostic markers. Somatosensory evoked potentials (SEPs) have been successfully used to evaluate central conduction in a number of d iseases involving the spinal cord. Objectives: To assess the diagnostic yie ld of SEPs in AIDS-associated myelopathy. Methods: We recorded tibial and m edian nerve SEPs in 69 HIV-infected subjects referred for evaluation of low er extremity neurologic abnormalities. Stimulation of the peroneal nerve at the popliteal fossa was performed in patients with absent response to ankl e stimulation. Results: HIV-infected subjects had significantly delayed lat encies of both peripheral and central potentials, suggesting a combination of peripheral and CNS abnormalities. Analysis of peripheral and central lat encies allowed us to discriminate between neuropathy and myelopathy in indi vidual patients. Abnormalities of tibial central conduction time (CCT) corr elated with clinical diagnosis of myelopathy. There was no significant diff erence in median CCTs between patients and controls, suggesting that conduc tion abnormalities were restricted to the thoracolumbar spinal cord. A deri ved spinal conduction time was a sensitive indicator of central conduction abnormalities in AIDS patients with myelopathy. Conclusions: The combinatio n of median, posterior tibial, and peroneal SEPs is a valuable tool in the diagnosis of AIDS-associated myelopathy, particularly when myelopathy and p eripheral neuropathy coexist. The use of a derived spinal conduction time i mproves the diagnostic yield of SEPs in AIDS-associated myelopathy.