We illustrate here a rare case of paraneoplastic limbic encephalitis in bronchogenic carcinoma where the patient presented primarily with neurological symptoms of encephalitis. We have described the radiological findings of the case.
Keywords: Bronchogenic carcinoma, encephalitis, magnetic resonance imaging, paraneoplastic
|How to cite this article:
Gupta S, Mittal A, Mittal G, Jain A. Paraneoplastic limbic encephalitis in bronchogenic carcinoma: A rare case report. Ann Trop Med Public Health 2012;5:250-2
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Gupta S, Mittal A, Mittal G, Jain A. Paraneoplastic limbic encephalitis in bronchogenic carcinoma: A rare case report. Ann Trop Med Public Health [serial online] 2012 [cited 2020 Aug 5];5:250-2. Available from: https://www.atmph.org/text.asp?2012/5/3/250/98630
Non-metastatic manifestations of internal malignancy (paraneoplastic syndromes) are not uncommon. Paraneoplastic neurological syndromes, however, are rare. Paraneoplastic limbic encephalitis is frequently associated with bronchial carcinoma and considered a particular manifestation of paraneoplastic encephalomyelitis, which includes involvement of other areas in the central (pyriform cortex, frontal orbital surface of the temporal lobe, insula, cerebellum, brain stem) and peripheral nervous system.  Patients with paraneoplastic limbic encephalitis present with subacute cognitive dysfunction, severe memory impairment, seizures, and psychiatric features including depression, anxiety, and hallucinations. A diagnosis of paraneoplastic limbic encephalitis must be considered in the differential diagnosis of unexplained dementia and appropriate investigations should be performed to diagnose the condition.
A 45-year-old male patient presented with loss of consciousness for 5-10 minute after an episode of convulsion in emergency. The patient had similar episode of generalized tonic-clonic convulsions for last one week. There was a history of short-term memory loss for last six months. There was also change in behavior of the patient as informed by attendants. On examination, he was disoriented to time, place, and person. There was no sensory or motor deficit. Bowel and bladder functions were normal. There was no history of fever, cough, or sore throat. There was no history of dyspnea or hemoptysis.
Patient was sent for a Magnetic Resonance Imaging (MRI) of the brain. On MRI, there were areas of gyral edema and hyperintensities on T2-weighted (T2W) sequence [Figure 1] in bilateral temporal lobes more on the right side, with small hypointense areas also noted in these areas. The lesions were hypointense on T1 and T1 Fluid Attenuated Inversion Recovery (FLAIR) sequences [Figure 2] and [Figure 3] with areas of gyral hyperintensities in both temporal lobes and large hyperintense area seen in the posteromedial aspect of the left temporal lobe. Therefore, MRI findings were diagnostic of bilateral hemorrhagic temporal encephalitis.
|Figure 1: T2W axial images (Figure 1a-c) of MRI are showing gyral edema with hyperintensities with few isointense to hypointense areas in bilateral temporal lobes|
|Figure 2: T1 FLAIR axial images of MRI (Figure 2a, b) showing gyral edema with hypointense areas with hyperintense areas and areas of gyral hyperintensities in bilateral temporal lobes|
|Figure 3: T1W axial image showing gyral edema with areas of bleed in temporal lobes|
Subsequently, radiograph of the chest [Figure 4] was done, which showed a large mass at the right hilum, with opacity and haziness in remaining areas of the right lung with pulled trachea and reticulonodular opacities in the left lung. Therefore, we suspected bronchogenic carcinoma on the right side. An ultrasonography of abdomen was then performed, which revealed target lesions in the liver suggestive of liver metastasis [Figure 5]. The final provisional radiological diagnosis was bronchogenic carcinoma with liver metastasis and paraneoplastic limbic encephalitis.
|Figure 4: Chest-Posterior-Anterior (PA) radiograph showing a large mass at right hilum, with opacity and haziness in the remaining areas of the right lung with pulled trachea and reticulonodular opacities in the left lung
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|Figure 5: Ultrasonography showing multiple target lesions (metastasis) in the liver|
Bronchoscopy was performed and biopsy was taken from the right hilar mass; histopathology showed small cell bronchogenic carcinoma. Thus, the final diagnosis was small cell bronchogenic carcinoma with liver metastasis and paraneoplastic limbic hemorrhagic encephalitis.
Paraneoplastic Neurological Syndromes (PNNS) are remote neurological effects of cancer caused by immune or other mechanisms, and are not due to direct tumor invasion, opportunistic infections, complications of drugs or radiotherapy, or malnutrition. PNNS may precede or follow the diagnosis of a tumor by weeks to months. , PNNS can involve the brain, spinal cord, peripheral nerves, neuromuscular junction, or muscles, separately or in various combinations. Of these, paraneoplastic limbic encephalitis is characterized by profound memory impairment, dementia, seizures (usually complex-partial type) and psychiatric disturbances including depression, personality changes, and loss of social inhibition. Three-quarters of the cases are associated with small cell carcinoma of the lung. Other tumors known to be associated are transitional cell carcinoma of the bladder, mediastinal teratoma, malignant thymoma, and testicular carcinoma.
Paraneoplastic limbic encephalitis is believed to be caused by autoimmune mechanisms involving reactions against antigens co-expressed by tumor cells and neurons. Specific antineuronal antibodies have been detected ,,,, in limbic encephalitis. The antineuronal antibody type 1, also called the anti-Hu antibody, in the cerebrospinal fluid and serum is highly associated with small cell lung carcinoma.  Anti-Hu is a polyclonal complement-fixing Immunoglobulin G (IgG) directed against a 35-40 kD protein concentrated in the nuclei of neurons throughout the central and peripheral neuraxes. It has been postulated that the auto-antibodies cross-react with antigens on normal cells, such as the neurons, resulting in tissue-specific cytotoxicity, or can form complexes with a circulating antigen to induce end-organ damage through immune complex deposition.
Other causes of encephalopathy such as metastases, drug neurotoxicity, infectious diseases (eg, herpes encephalitis), and meningeal carcinomatosis must be excluded.
MR imaging-based diagnosis of paraneoplastic limbic encephalitis requires depiction of signal intensity changes of the temporobasal region as noted in our case. On T1 sequences, temporal-limbic regions may be hypointense and atrophic. In addition, gyral enhancement is present in more than half of the patients and signs of hemorrhage are not uncommon as seen in our case. 
Therefore, paraneoplastic limbic encephalitis is an important differential diagnosis in limbic encephalitis cases and patients should be investigated if clinical findings and radiological investigations point to that diagnosis.
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