Case Presentation: A previously healthy 20 year old female presented to the emergency department for change in mental status. Five days prior to presentation, the patient was diagnosed at a local urgent care facility with Infectious Mononucleosis and discharged with a course of Prednisone 20 mg. Per family, since starting steroid therapy she began developing acute changes which were very uncharacteristic compared to her baseline mental status. On presentation, the patient was noted to be pressured, tangential, and difficult to re-direct.Upon ED presentation, the patient’s vitals were hemodynamically stable. Laboratory values revealed leukocytosis with elevated neutrophil count of 7.92. CT Head without contrast was negative for acute intracranial pathologies. On neurology exam, findings were consistent with telegraphic speech, Broca’s aphasia, dysarthria, ataxia, uncoordinated balance, dysmetria on finger-to-nose and heel-to-shin test, and bilateral dysdiadokinesia. with hysterical laughing, was poorly redirectable, and had disorganized speech and behavior indicating hospitalization for acute mania in the setting of acute encephalopathy.

Discussion: Post EBV acute cerebellitis is a very rare complication of Infectious mononucleosis, mainly documented in the pediatric population, but highly rare in adults.(1-3) The pathophysiology is mainly based on autoreactive antibodies instead of a direct viral invasion. Plausible mechanisms involve antineuronal antibody formation against EBV proteins that can mimic neuronal antigens, or secretion of these antibodies by EBV- transformed Lymphocytes.(3)Patient presentation may vary between cases, previous reports presented a variety of clinical symptoms including headache, nausea, vomiting, vertigo, diplopia, ataxia, bradycardia, nystagmus, dysarthria and altered mental status.(1, 4) In the above case, the patient had an atypical presentation with dysarthria and uncontrolled laughing with disinhibition. Daily assessments raised concerns due to clinical decompensation and new onset of ataxia, dysdiadokinesia, and dysmetria which indicated a neurologic etiology. Careful review of history was a key factor in the above case with recent EBV infection. MRI is considered as the main diagnostic test for acute cerebellitis and typically shows abnormal signals on T1-weighted images, with diffuse cortical swelling of the cerebellum or with leptomeningeal enhancement.(5, 6) In case of negative MRI findings, a lumbuar puncture may be performed showing lymphocytosis and, in some cases, a positive EBV PCR. (1, 7) Regarding treatment, there is no established therapeutic protocol for EBV- associated cerebellitis due to paucity of adult cases. In general, it is considered benign and self-limiting. Previous reports recommended the initiation of acyclovir in EBV CNS infection.(8) Corticosteroids use has been equivocal in EBV infection although it is recommended in patients with encephalitis or acute demyelinating encephalomyelitis.(5)

Conclusions: It is crucial to maintain a wide differential when faced with an atypical presentation. A high index of suspicion is critical to rule out an underlying acute neurologic disorder before proceeding with a psychiatric diagnosis that would exhaust many resources and delay patient care. Post EBV cerebellitis is to be considered in a patient with recent EBV infection who presents with dysarthria and ataxia. Corticosteroid therapy may be beneficial in speeding recovery