Specific Imaging Findings

In limbic encephalitis (LE), the mesial temporal lobes show bright T2 signal and may appear swollen or of normal width. Contrast enhancement is commonly absent, but when present may be patchy or have a bizarre configuration and distribution. About 50% of patients show bilateral involvement, often asymmetrical. The lesion may extend from the amygdala to the tail of the hippocampus. Other areas which are occasionally involved include the parahippocampal gyrus, temporal white matter stem, thalamic pulvinar, dentate nuclei and cerebellar cortex. With the passage of time, the signal abnormality resolves (although not completely in many patients) and the affected area loses volume. ADC measurements have been inconclusive and thus not helpful, while high signal intensity in DWI is thought to be due to shine-through phenomenon. Proton MR spectroscopy may show low n-acetylaspartate, normal choline and occasionally high glutamate/glutamine and lactate. In some patients, all metabolites are low.

Pertinent Clinical Information

Symptoms tend to start relatively acutely and include: cognitive dysfunction, recent memory difficulties, hallucinations, bizarre behavior, seizures, sleep disturbances, and speech disturbances. Symptoms are present in about 80% of patients who have an abnormal MRI study. The symptoms may be similar to those seen in Alzheimer and Creutzfeldt–Jakob diseases but their more acute onset and the presence of underlying neoplasias helps differentiate among them. To make the diagnosis, CSF must be free of malignant cells, viruses and other pathogens.