OVERVIEW
Paraneoplastic limbic system encephalitis is a distant effect of a systemic carcinoma appearing in the central nervous system (CNS) and muscular system, which presents clinically as an amnesic syndrome when the limbic system is predominantly involved.
Etiology.
The primary tumors for this disease are small cell lung cancer or Hodgkin’s disease, and malignant thymoma can sometimes lead to this disease. Its etiology is unknown, but anti-neuronal autoantibodies have been found to be involved in other paraneoplastic neurologic syndromes.
Symptoms
The characteristic symptoms of this disease are progressive dementia and marked memory impairment, especially for recent events, but also generalized seizures, myoclonus, speech disorders and cerebellar signs. In addition to the corresponding cerebral nerve palsy, brainstem inflammation may present with central hyperventilation.
The clinical presentation of amnesic syndrome due to paraneoplastic limbic encephalitis can be static, progressive or recurrent. The patient’s clinical presentation is characterized by severe impairment of proximate memory and a marked decrease in the ability to learn new things. Distant memory impairment is generally mild and the ability to record is unaffected. Amnesia can be present in some cases with anxiety and depression, usually early in the appearance of the syndrome, and hallucinations as well as partial or generalized seizures can also be present. In many cases the amnesic syndrome progresses until dementia develops.
Paraneoplastic limbic encephalitis is most often associated with small cell lung cancer, and the onset of the syndrome usually precedes the discovery of the lung cancer.
Tests
1. Laboratory examination
(1) A small amount of mononucleated cells in the cerebrospinal fluid and a moderate elevation of protein.
(2) Serologic tests sometimes reveal an antibody against the neuronal Ma2 protein.
2. Other auxiliary tests
(1) EEG sometimes shows diffuse slow waves or the presence of slow waves or spikes in both temporal lobes.
(2) MRI shows abnormal signal images in the middle temporal lobe, hippocampal cingulate gyrus, insula, and amygdala.
(3) Histologic examination revealed neuronal loss, reactive gliosis, microglia, and peripheral vascular lymphocyte infiltration in the form of nests in the cerebral cortex. Gray matter in the hippocampal cingulate gyrus, pyriform cortex, inferior frontal lobe, insula, and amygdala are the most common sites of damage.
Diagnosis
1. mainly based on the clinical signs and symptoms of amnesia syndrome due to limbic encephalitis in the patient.
2. Presence of a primary tumor.
Treatment
Symptoms of limbic lobe encephalitis may resolve after resection of the primary tumor or chemotherapy, and plasma exchange may be effective. There is no specific treatment, so treatment of the primary tumor is particularly important.
Particular attention should be paid to organic amnesic syndrome due to vitamin B1 deficiency, because cancer patients often suffer from severe nutritional deficiencies, and treatment with high levels of vitamin B1 may ameliorate the worsening course of the amnesic syndrome.
Prognosis
Correlates with the prognosis of the systemic tumor causing the syndrome; it also correlates with the extent of damage to the limbic system. Prognosis varies. Treatment with large amounts of vitamin B1 may improve the deteriorating course of the amnesic syndrome.