What is the current role of a Wada test in the pre-surgical work-up of pharmacologically intractable epilepsy in adults?

Juhn Wada developed a test while in Montreal designed to definitively confirm hemispheric lateralization of speech in candidates for surgical treatment of epilepsy. By unilateral intra-carotid administration of a bolus of a general anesthetic, clasically sodium amobarbital, function can be tested in the non-injected hemisphere, while the injected side is dysfunctional. The test has been expanded to test memory functions in the hemisphere (temporal lobe) contralateral to expected surgery (memory reserve) in the hope of contra-indicating surgery that may result in global amnestic syndromes (patient HM). Conversely, risk of material-specific memory loss following surgery can be assessed by testing memory in the hemisphere/temporal lobe to be operated ('functional adequacy). Memory dysfunction, when concordant with EEG seizure onset and chosen side of temporal lobe surgery has also been shown to correlate with favourable post-operative seizure outcome. Nevertheless, the test remains invasive, requiring an angiogramme. Non-invasive alternatives such as fMRI and PET and their reported reliability compared to a Wada test are discussed. A world-wide shortage of amobarbital has led to the use of some other anesthetic agents. Overall, the indications for the test and the manner in which it is performed vary greatly from one institution to the next. It is used almost systematically in some institutions and very rarely in others. Future perspectives are discussed.