A case of long-lasting but reversible isolated amnesia of unknown aetiology

Abstract

We report the case of a 64-year-old man with an acute isolated and prolonged transient amnesic state. The underlying aetiology remained obscure. Brain magnetic resonance examination demonstrated only non-specific slight and transitory signal intensity abnormalities within the left hippocampus on T2-weighted images. Electroencephalographic studies showed repetitive periodical and prolonged bursts of rhythmic theta activity, originating from the left fronto-temporal region, but no typical epileptiform discharges. As an epileptic origin could not be excluded, anti-epileptic treatment was administered. Subsequently, electroencephalographic abnormalities disappeared completely after a few days. On follow-up, repetitive clinical and neuropsychological comprehensive evaluations showed that the mnesic capacities improved slowly and gradually. The gradual improvement concerned time and place orientation first of all and was followed thereafter by improvement of explicit memory and the capacity to learn new information. Clinically, at this stage, the patient appeared appropriately orientated, according to the medical staff and his family, although memory tests remained abnormal. The memory deficit lasted -3 months but was followed by complete recovery. In our discussion, we consider possible aetiologies for transient amnesia with emphasis on an epileptic as opposed to a vascular aetiology by focal hippocampal ischaemia.