Paraneoplastic limbic and extra-limbic encephalitis secondary to a thymoma mimicking an acute stroke

Abstract

Paraneoplastic neurological syndromes (PNS) occur in one in ten thousand patients with malignancy.1 These syndromes are defined by dysfunction remote from the tumor site that cannot be explained by metastasis, treatment or infection. 2 The dysfunction in PNS is believed to be a result of neoplastic immune-mediated injury to neural tissue. Antibodies may be created against proteins on cancer cells that are usually only expressed in the nervous system. Paraneoplastic neurological syndrome is thought to develop when these antibodies cross-react and trigger an autoimmune response in normal neural tissue.2 Presence of onconeural antibodies, clinical onset around the diagnosis of cancer and improvement with treatment of the cancer favors the diagnosis of PNS. Thymoma is a common anterior mediastinal malignancy. Approximately 40% of cases of thymoma are associated with PNS. 3 The most common and well-known form of PNS in patients with thymoma is myasthenia gravis (MG). In MG the thymus can be the antigenic source for antibodies that disrupt neurotransmission. 4 The most common antibodies found in MG are against the postsynaptic acetylcholine receptor or the muscle specific tyrosine kinase 4 Around 15% of patients with a thymoma have a paraneoplastic process other than myasthenia gravis.3 Paraneoplastic involvement of the central nervous system is an uncommon and less recognized presentation of thymoma. We report a rare case of limbic and extra-limbic paraneoplastic encephalitis with a thymoma. CASE REPORTA 47-year old male presented at the emergency room of a teaching tertiary care hospital with a two-day history of psychotic symptoms consisting of hallucinations, delusions, false memories and disorganized behavior. Patient had past medical history of fatigable weakness limited to the eyelids or extraocular muscles for six months and a brief psychotic episode 20 years earlier. On examination his oxygen saturation was 92% at room air (venous blood gas pH 7.4, pCO 2 40 mmHg, HCO 3 25 mEq/L). He had frontal release signs including positive involuntary grasp and a positive Luria's test. An unenhanced computed tomography (CT) brain scan was performed and demonstrated a left-sided 12mm hypodense lesion in the frontal lobe (Figure 1a). This was interpreted as suspicious for an acute infarction. The patient was admitted to hospital under the Neurology service and had worsening psychotic symptoms. On day six, an unenhanced CT brain scan was repeated and demonstrated progression of the leftsided hypodense lesion that was interpreted as compatible with an evolving infarct (Figure 1b). Based on the results of this CT brain scan, a magnetic resonance imaging (MRI) scan of the brain was not immediately ordered.On day 11, carotid Doppler and transthoracic echocardiography did not reveal any cardiovascular abnormality, but transthoracic echocardiography did demonstrate a large extracardiac mass. On day 14, contrast-enhanced CT of the thorax confirmed an 11 × 10 × 8 cm mediastinal mass lateral to the left border of the heart with soft ...

Thymoma‐associated autoimmune encephalitis: Analysis of factors determining prognosis

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