Transient Epileptic Amnesia - Diagnosis

Diagnosis

Transient amnesia can be the principal manifestation of epilepsy. This diagnosis, however, is "seldom suspected by clinicians and remains controversial." TEA is "almost always misdiagnosed" according to a leading authority. In the largest study to date (2007) "Epilepsy was the initial specialist diagnosis in only 12 of 50 cases." Diagnosis is further complicated by the fact that only somewhat more than a third of cases present positive EEG readings after the attack. However, as TEA tends to recur at a median rate of 12 times a year, witnesses and clinicians may be able to recognize the condition retrospectively; the median delay to diagnosis of TEA in the 2007 study was 12 months.

TEA is a form of focal seizure, which are "the most common variety of adult-onset epilepsy" as opposed to the stereotypical tonic-clonic or grand mal seizure in which affected persons suffer loss of consciousness and convulse. Diagnostic criteria for the disorder were adopted in the 2007 study of 50 case emphasized clinical features that distinguish TEA from Transient global amnesia (TGA), with which TEA is often compared:

• A history of recurrent witnessed episodes of transient amnesia. In some people, they are very infrequent (less than one per year) whereas others experience them as often as once a week. The episodes are usually very similar to each other.
• Cognitive functions other than memory judged to be intact during typical episodes by a reliable witness. In addition to the complex learned behaviors cited above by the TIME organization, reports include people with TEA sight-reading music and playing piano, translating languages, driving or sailing a yacht in the open sea.
• Evidence for a diagnosis of epilepsy based on one or more of the following:
  • Epileptiform abnormalities on electroencephalography (EEG). In a survey of all known cases, 43.6% have epileptiform abnormalities localised over the temporal or fronto-temporal region on electroencephalography following the attack. Of these, 31.7% were left-sided, 12.2% were right-sided and 56.1% were bilateral.
  • The concurrent onset of other clinical features of epilepsy (e.g., lip-smacking or other involuntary automatic behaviors, olfactory hallucinations). Approximately 40% of people with TEA report one of these symptoms in at least some attacks.
  • A clear-cut response to anticonvulsant therapy. Attacks ceased in 44 of 47 treated patients in one study.