Case Presentation: A 29 year old woman presented with a generalized tonic clonic seizure and progressively worsening ataxia over the last six months. She also had memory deficits and diplopia. Her past medical history included Li Fraumeni syndrome and an immature ovarian teratoma that was treated with a right oophorectomy and chemotherapy in 2015. Her vital signs were normal except for a mild tachycardia. She was cachectic, wheelchair-bound but in no acute distress. She was alert and oriented; had direction changing nystagmus; restricted extraocular movements in all directions in both eyes; ataxic gait, and mildly decreased strength in her lower extremities. She also had dysmetria, a positive Babinski’s sign, and dysesthesia to pinprick over her left thigh/abdomen. The remainder of her exam was normal. Cerebrospinal fluid (CSF) analysis was significant for a lymphocyte predominant pleocytosis but was negative for a central nervous system infection and the CSF paraneoplastic panel was also negative. There was an abnormal T2 signal in the bilateral medial temporal and occipital lobes concerning for autoimmune or infectious encephalitis on an MRI of her brain. No spinal cord abnormalities were seen on cervical, thoracic, or lumbar MRI. A PET scan showed hypermetabolic areas in her abdomen and a retroperitoneal lymph node concerning for malignancy and a biopsy was consistent with a metastatic immature teratoma. The patient was empirically treated for autoimmune encephalitis based on her presentation and high clinical suspicion and the presence of the recurrent immature teratoma. Her symptoms improved after treatment with pulse dose steroids, plasmapheresis, Rituximab, and initiation of chemotherapy for the teratoma. Subsequently, a previously unclassified CSF restricted autoantibody was found per results from the Mayo Clinic.
Discussion: Autoimmune encephalitis is caused by antibodies against neuronal cell surface or synaptic proteins and it usually presents with various neurologic or psychiatric symptoms and can occur with or without an underlying malignancy. Younger patients are more likely to have a concomitant malignancy. Early diagnosis and treatment with immunosuppressive therapy and treatment of the underlying malignancy, if present, have been shown to improve outcomes. The finding of a newly discovered autoantibody in this patient’s CSF is significant because it suggests that there are likely many more antibodies capable of causing autoimmune encephalitis that have yet to be discovered. Consequently, autoimmune encephalitis is likely an underdiagnosed entity and more resources should be focused on identifying additional novel antibodies capable of causing this disease so that cases are accurately diagnosed and early treatment can be initiated. It also provides anecdotal evidence that a negative CSF autoantibody panel does not necessarily rule out a diagnosis of autoimmune encephalitis since it could be caused by an autoantibody that has yet to be discovered.
Conclusions: Patients presenting with seizures and neurologic findings such as ataxia, memory deficits, and diplopia are commonly seen by hospitalists and autoimmune encephalitis should be considered in the differential diagnosis.