|Year : 2017 | Volume
| Issue : 2 | Page : 277-279
Magnetic resonance imaging features of paraneoplastic limbic encephalitis
Department of Radiology, St. John's Medical College, Bengaluru, Karnataka, India
|Date of Web Publication||9-Jan-2018|
Dr. Reddy Ravikanth
St. John's Medical College, Bengaluru - 560 034, Karnataka
Source of Support: None, Conflict of Interest: None
Paraneoplastic limbic encephalitis is a neurological syndrome characterized by seizures, rapidly progressive short-term memory loss and psychiatric symptoms. It may present in association with cancer, infection, or as an isolate clinical condition. Definite diagnosis requires either cerebrospinal fluid analysis or neuroimaging evidence of the involvement of the limbic system besides the clinical features. Here, we present the imaging features of limbic encephalitis.
The following core competencies are addressed in this article: Medical knowledge, Patient care.
Keywords: Cerebrospinal fluid analysis, electroencephalogram, magnetic resonance imaging, paraneoplastic limbic encephalitis
|How to cite this article:|
Ravikanth R. Magnetic resonance imaging features of paraneoplastic limbic encephalitis. Int J Acad Med 2017;3:277-9
| Introduction|| |
Paraneoplastic limbic encephalitis (PLE) is a rare entity characterized by subacute onset of seizures, short-term memory loss, confusion, and psychiatric symptoms, suggesting the involvement of the limbic system. PLE usually affects older patients with lung cancer (50%). 20% incidence has been reported in patients with testicular tumors and 8% of patients with breast cancer. Younger individuals typically have the germ cell tumors of the testis or ovarian teratomas. Most cases of PLE have occurred in association with small cell lung cancer, and 50% are associated with anti-Hu antibodies. Germ cell tumors usually have more dominant limbic, diencephalic, and upper brainstem dysfunction. Hodgkin's lymphoma, immature teratoma, and thymoma are the most frequently associated tumors. Magnetic resonance imaging (MRI) abnormalities in the medial temporal lobes are helpful in confirming a diagnosis of limbic encephalitis, but normal imaging does not exclude the diagnosis.
| Case Report|| |
A 40-year-old female presented with 3-week history of irritability, generalized seizures, numbness and tingling of hands and feet. She gave a history of tobacco smoking for 10 years. Electroencephalogram showed bilateral temporal intermittent rhythmic delta activity with disorganization and slowing of background activity. No periodic lateralized epileptiform discharges noted. On examination, vitals were stable with no fever. Cerebrospinal fluid (CSF) analysis revealed lymphocytic pleocytosis (>5 cells/mm 3), elevated proteins (>45 mg/dl). No red blood cells were noted in the CSF. Results of herpes simplex virus polymerase chain reaction done on CSF were negative. CSF was examined for paraneoplastic antibodies and showed positivity. CSF gram stain did not reveal any pathological agent. Infectious panels done on CSF for neurosyphilis, herpes, and varicella/zoster were negative. Gadolinium-enhanced MRI done in a closed magnet revealed subcortical T2 fluid-attenuated inversion recovery (FLAIR) hyperintensities in bilateral insular cortices, bilateral dorsomedial thalami [Figure 1], the white matter of bilateral temporal lobes [Figure 2] and T2 hyperintensities in bilateral hippocampi [Figure 3] with prominent right temporal horns showing minimal contrast enhancement suggesting an autoimmune etiology or a metabolic encephalopathy. Symptoms and pathological findings of limbic encephalitis have been reported in the absence of cancer. The patient showed no improvement with Acyclovir treatment. The differentials considered were hepatic encephalitis and paraneoplastic syndrome. Patient's liver function tests were not deranged excluding a possibility of hepatic encephalitis. Chest computed tomography (CT) showed a right paratracheal lymph node mass that was confirmed with chest MRI. In addition, serological tests for onconeuronal antibodies revealed autoantibodies to Hu. Thoracic surgeon consultation recommended a thoracotomy, where a biopsy demonstrated a large cell neuroendocrine carcinoma. The patient was treated with intravenous corticosteroids, carboplatin, and etoposide and was discharged with 40 mg prednisolone od, 500 mg valproic acid tid, 500 mg levetiracetam bid, and 25 mg quetiapine at night. Six months later, he had complete tumor remission as demonstrated in the chest CT.
|Figure 1: Axial T2 fluid-attenuated inversion recovery image showing hyperintensities in bilateral insular cortices and dorsomedial thalami|
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|Figure 2: Axial T2 fluid-attenuated inversion recovery image showing cortical hyperintensities in bilateral temporal lobes|
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|Figure 3: Coronal T2 weighted fast spin echo image showing hyperintensities in bilateral hippocampi|
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| Discussion|| |
Most common initial typical findings of limbic encephalitis are T2 hyperintensity and swelling of the limbic structures, though extratemporal involvement does not preclude a diagnosis of this condition. Pathologic changes of the brain are found not only in limbic structures but also in the pyriform cortex, frontal orbital surface of the temporal lobe, and insula. Serial MRI should be considered in patients with suspected limbic encephalitis to demonstrate the delayed development of radiologic changes in patients who previously had normal MRI imaging findings, evolution of changes involving the contralateral side, suggesting ongoing inflammatory activity radiologically, and progression to mesial temporal sclerosis.
PLE is a rare entity characterized by subacute onset of seizures, short-term memory loss, confusion and psychiatric symptoms, suggesting the involvement of the limbic system. T2 weighted imaging and FLAIR techniques are useful in revealing the encephalomyelitis of the mesial temporal lobes and other areas of the brain. These imaging techniques should be used whenever hippocampal pathologic abnormality is suspected. Restricted diffusion in the temporal lobes can be seen with recent seizure activity or status epilepticus. Most patients with autoimmune or PLE have unilateral or bilateral increased T2/FLAIR signal in the medial temporal lobes without contrast enhancement or abnormal diffusion-weighted images; an exception is the paraneoplastic encephalitis with antibodies against the intracellular protein Ma2, in which MRI often shows contrast enhancement. In the immunocompetent adult patient, herpes simplex encephalitis pattern is quite typical and manifests as a bilateral asymmetrical involvement of the limbic system, medial temporal lobes, insular cortices, and inferolateral frontal lobes. The basal ganglia are typically spared, helping to distinguish it from a middle cerebral artery infarct.
The classic mechanism reported in PLE is a systemic neoplasia that expresses coincident antigens within the central nervous system, which results in the production of antibodies that target neoplastic tissue (onconeural antigens) as well as intracellular antigens. The correct diagnosis of PLE is relevant because earlier recognition often allows the discovery and treatment of the underlying malignancy. Cancer control is a crucial step in the management of PLE, which is usually followed by the remission of the paraneoplastic syndrome.
| Conclusion|| |
MRI demonstrates T2 FLAIR hyperintensities predominantly involving the hippocampi in limbic encephalitis. MRI reveals the involvement of affected structures suggests the diagnosis of limbic encephalitis and monitors response to therapy. MRI in limbic encephalitis should be interpreted cautiously because of the overlap with other entities. In 60% of the patients with PLE, the syndrome precedes the detection of the tumor, further complicating the diagnosis.
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Conflicts of interest
There are no conflicts of interest.
Ethical conduct of research
The authors attest that this scholarly work was conducted in accordance with the recommendations of The International Committee of Medical Journal Editors. Patient consent was obtained prior to the submission of this manuscript for publication in the International Journal of Academic Medicine.
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