In a small number of cases, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for emotions and many other basic functions), often causing memory deficits similar to those observed in Alzheimer's disease or Creutzfeldt-Jakob disease (although limbic encephalitis does not cause the same cognitive deficits as these diseases.
60% of the time, limbic encephalitis is paraneoplastic in origin.
Paraneoplastic limbic encephalitis (PLE) is a particularly severe form of limbic encephalitis caused by neoplasms most commonly associated with small cell lung carcinoma. Whereas the majority of encephalitides are viral in nature, PLE is often associated with cancer. In fact, it is thought that up to 1 in 100 people with cancer have paraneoplastic limbic encephalitis which is commonly misdiagnosed as neurological diseases such as Alzheimer's.