The base rate of Wada test failure

Although functional brain imaging can lateralize language functioning and has the potential to assess the functional integrity of the mesial temporal lobe memory structures, imaging protocols are not currently available for clinical use. Assessing the risk of post-epilepsy surgery memory decline is an important part of treatment planning, and the Wada test remains the current technique. The Wada test is invasive and has limitations with respect to sensitivity and specificity. We describe an audit of 141 consecutive Wada test results looking at the base rate of failure and clinical characteristics of failure. The objective was to provide base rate data that support decision making regarding selective use of the Wada test. We conclude that right-handed patients with right temporal lesions who have strong verbal memory are very unlikely to fail and probably do not need to undergo the Wada test. Patients with left temporal lesions are more likely to fail regardless of handedness and regardless of baseline neuropsychological test data. We propose that until functional imaging protocols become available to supersede the Wada test, patients should be considered for the Wada test on a case-by-case basis.