GABA-B receptor encephalitis is a cell surface mediated paraneoplastic disease secondary to antibody production resulting in neuronal cells loss, microglial proliferation, and preferentially targets the limbic system. Symptoms include seizures, memory loss, confusion, and altered behavior. The infrequency with which it is encountered can create a diagnostic challenge.

Case Description:

A 73-year-old female presented as a referral months post hospitalization and outpatient evaluation. Initial presentation began with subacute progressive disorientation, crying spells, ageusia, anosmia, and memory loss without a known precedent illness. On initial exam she was alert, oriented only to self, inattentive, and without other focality.

The results of the work up included contrasted MRI demonstrating T2 hyperintensities within the hippocampi. Lumbar puncture revealed antibodies against GABA-B receptors. High dose steroids were initiated with minimal improvement therefore IVIG was trialed in the outpatient setting resulting in stabilization and moderate improvement of symptoms. A PET scan was requested and revealed a mass within the left lower lobe of the lung. Biopsy identified features of small cell carcinoma confirming our suspicion of encephalitis secondary to paraneoplastic syndrome.

Currently she is undergoing oncological evaluation and treatment. Symptoms remain stable, but emotional lability, poor short-term recall, ageusia and anosmia persist. No additional IVIG or long-term immunotherapy was initiated as treatment should be targeted toward the malignancy. She will remain under neurological surveillance with serial exams and MRIs.  

This case illustrates the importance of recognizing alternative causes of encephalitis. Localizing limbic symptoms were present although the lack of seizures and presence of ageusia and anosmia is highly unusual. We also discovered an extensive smoking history and family history of lung cancer. These red flags highlight the need for a complete history. Early consideration of a paraneoplastic process causing encephalitis will facilitate additional diagnostic testing, prompt initiation of immunotherapy and accurate diagnosis.