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Limbic encephalitis typically presents with subacute development of memory impairment, confusion, and alteration of consciousness, often accompanied by seizures and temporal lobe signal change on MRI. There is however no clear consensus as to the definition; even traditional distinctions between “encephalitis” and “encephalopathy”, and between “delirium” and “dementia” may be blurred in such patients.
The term limbic encephalitis was initially coined to describe patients presenting with amnesia, psychiatric disturbances, and often seizures, and who had postmortem evidence both of occult neoplasia and fairly selective inflammation within the temporal lobes.1 More recently, however, it has also been used to describe patients with a similar phenotype but in whom an infectious or non-paraneoplastic autoimmune cause has been proven or suspected. Even in “typical” paraneoplastic limbic encephalitis, selective involvement of the limbic structures (hippocampus, amygdala, hypothalamus, insular and cingulate cortex) is often not proven histologically, but has been inferred from the clinical presentation and investigations including MRI and EEG. Conversely, although medial temporal lobe MRI and EEG abnormalities are commonly seen, these may not always be present in patients with typical paraneoplastic limbic encephalitis.2
From a practical perspective, limbic encephalitis can be viewed as a syndrome of subacute onset—usually over days or weeks, at most a few months—with a range of underlying causes, the clinical features including:
cognitive, and particularly memory, impairment predominantly due to involvement of the limbic system
frequent but not invariable seizure activity arising from one or both temporal lobes
frequent but not invariable MRI signal change within limbic structures, particularly the hippocampus.
This review aims to provide an overview of the important underlying causes that should be considered in patients presenting in this fashion, with particular reference to some of the recently described autoimmune findings. Although in many cases there is limited evidence to guide management, some …