The case of an elderly woman who had mental problems associated with Alzheimer's disease, but turned out to have treatable limbic encephalitis, is detailed in a Case Report in this week's edition of The Lancet. The case is important because, with rapidly increasing numbers of elderly people worldwide, it is important that when they present with such symptoms they are correctly diagnosed and not just assumed to have Alzheimer's disease (or typical dementia). The Case Report is written by Dr Nathalie Costedoat-Chalumeau, Centre Hospitalier Universitaire Pitie-Salpetriere, Paris, France, and colleagues.
The then 70-year old woman presented to hospital in July 2007 with a 4-month history of confusion and episodic memory loss, but no past medical history. Physical and neurological examinations were normal, but neuropsychiatric tests showed memory and learning problems. Blood analysis was normal, but an MRI revealed a hippocampus abnormality usually associated with limbic encephalitis. The patient was treated with cyclophosphamide infusions and steroids, and her symptoms improved. A relapse 18 months later was also treated successfully.
Limbic encephalitis is a brain disorder in which pathogens attack the limbic system, a collection of structures at the base of the brain responsible for emotions and many other basic functions. Limbic encephalitis can present as cognitive disorders with short-term memory impairmment, temporal seizures, and psychiatric disorders which progress over a few weeks.
The authors say: "In our case, the diagnosis could have been mistaken for Alzheimer's disease, especially since the brain CT scan was normal. However, the short period of evolution and associated MRI features were atypical for Alzheimer's disease, and led us to look for limbic encephalitis."
They conclude: "In the past, limbic encephalitis was considered a rare disease, often associated with cancer and unresponsive to treatment. Discovery of new antibodies and autoimmune mechanisms has brought immunosuppressive treatments that have improved prognosis, particularly in cases associated with antibodies to cell-membrane antigens. It should now be regarded as a non-exceptional and treatable aetiology of rapidly progressive dementia."