Limbic Encephalitis associated with Anterior Mediastinal Neuroendocrine Tumour.
Zac-Varghese, S., Chakrabarti, S., Perry, R., Hatfield, E., Sharma, R.
A 50 year old events planner, with a past medical history of ductal breast carcinoma, had a prolonged history of fatigue dating from Christmas 2012. Her breast carcinoma had been treated in 2006 with bilateral mastectomy, axillary node clearance, chemotherapy and radiotherapy and she was in remission.
Her fatigue progressively worsened and in April 2013 she was involved in a major car accident which was most likely caused by a loss of consciousness. In September, she was admitted to a local district general hospital with a reduced conscious level, GCS 10. She was found to be hyponatraemic and was diagnosed with SIADH. A pituitary profile revealed secondary hypothyroidism and hypocortisolaemia with a normal short synacthen test. A pituitary MRI did not reveal any pituitary abnormality. However, abnormal signal was seen around the diencephalon and the report suggested that the hypothalamus was affected. A preliminary diagnosis of limbic encephalitis was made and she was transferred to Charing Cross Hospital for further investigation and treatment.
In view of her previous breast cancer, it was felt that a recurrence was likely, leading to paraneoplastic limbic encephalitis. She had further investigations including EEG, sleep studies, lumbar puncture and spinal fluid analysis. The LP revealed the presence of anti-amphiphysin antibodies (present in para-neoplastic syndrome). Diagnostic imaging was obtained, including a PET-CT and this demonstrated the presence of a 2 cm anterior mediastinal mass. This was biopsied and the histology was reported as a grade 3 neuroendocrine tumour (NET), Ki 67 > 20 %, CD56 positive (this is a commonly used marker for NET). There was no evidence of recurrence of her breast carcinoma. The histology result and case were discussed at the NET MDT and the decision was made to start chemotherapy to treat the NET. Surgery was considered too risky given the location of the NET. In addition, she had previously undergone trials of plasma exchange and high dose steroids and these had not been successful. She is currently being treated with a regime of chemotherapy usually used to treat small cell lung carcinoma, is receiving octreotide, is on pituitary hormone replacement and is on a 1.5 L fluid restriction. She has also been referred for surgery and excision of the anterior mediastinal node and thymectomy at Hammersmith Hospital.
Limbic encephalitis associated with NET is rare and there have only been a few reported cases worldwide. Treatments include addressing the underlying malignancy, immunosuppression and correction of electrolyte and hormonal abnormalities.