Lesson of the month 2: Transient reversible amnesia in multiple sclerosis

Abstract

Transient amnestic syndromes are fascinating clinical entities and there are several subtypes. Transient global amnesia (TGA) is characterised by sudden onset of anterograde amnesia with repetitive questioning, lasting less than 24 hours. The pathophysiology of TGA involves the medial temporal lobes and hippocampi. Episodes of TGA are thought to involve venous congestion with Valsalva-like activities, vascular or migrainous mechanisms. In contrast, transient epileptic amnesia manifests as brief and frequent episodes of amnesia due to seizure activity in the temporal lobes. Transient memory disturbances can also be caused by transient ischaemic attack. We describe the first reported case of transient reversible amnesia directly attributable to acute demyelination. This case reminds us that multiple sclerosis relapses may present with acute cognitive impairment rather than the more classical physical symptoms. This is an important learning point in terms of appropriate management and eligibility for disease-modifying drugs.

Keywords: Anterograde amnesia; demyelinating disorders; multiple sclerosis; temporal lobe.

Fig 1.

Magnetic resonance imaging (MRI) scans of patient. A – MRI scan 4 months prior to the acute episode of amnesia. Axial MRI T2-weighted image shows subtle signal change lateral to temporal horn (left>right) with concomitant juxto-cortical signal change in the right occipital lobe. B – MRI scan 2 weeks after the onset of episode of amnesia. Axial MRI FLAIR sequence showed new areas of T2 high signal consistent with demyelination that predominantly affected both temporal lobes.