Objective:

A healthy adult male presenting with classic autoimmune encephalitis led to discovery of thymoma, with identification of novel neuronal antibody in cerebrospinal fluid (CSF).

Background:

A 44-year-old male presented with subacute onset of vertigo, headaches, subtle personality changes, short-term memory deficits, and an 11 pound weight loss.  He had two unprovoked seizures that were preceded by aura of left tongue and arm paresthesias, and a fixed delusion described as feeling a “string” on his left hand and tongue which he continuously attempted to remove.  Physical exam, MRI, and EEG were normal. Laboratory evaluation was notable for hyponatremia and CSF with elevated protein and pleocytosis.

Design/Methods:

NA

Results:

Due to suspicion for autoimmune encephalitis a CT chest/abdomen/pelvis was obtained, identifying a 5.3 cm pericardial mass abutting the mainstem pulmonary artery. Biopsy confirmed thymoma. He became increasingly psychotic and disoriented, with persistent symptoms involving left face and hand.  Despite negative EEG, these were treated as focal seizures and resolved. His other symptoms (insomnia, psychosis, and hyponatremia) were resistant to treatment.  He received IVIg and high-dose steroids.  Due to the complexity of thymoma location, neoadjuvant chemotherapy was recommended.  He was treated with cisplatin, doxorubicin, and cyclophosphamide coinciding with a second course of IVIg and high-dose steroids, after which his neurologic status slowly normalized over days. Eventually, his serum ACh-binding Ab was positive, as was striated muscle Ab IgG, with titer 1:1280.  Autoimmune panels of serum and CSF sent to Mayo Clinic identified cross-reactivity with neurochondrin, indicating a novel neuronal antibody pending further investigation.  He completed neoadjuvant chemotherapy and surgical planning for thymoma resection is underway.

Conclusions:

Patients with subacute onset of neurological decline may need evaluation for autoimmune encephalitis and paraneoplastic syndromes. With ongoing rapid expansion of antibody detection capabilities, it's important to describe phenotype-specific presentations of paraneoplastic encephalitis that may aid early detection of malignancy.