Case Presentation: A 52-year-old woman brought by family to the emergency department with worsening confusion over 24 hours. There were no associated symptoms and history negative for fever, headache, sore throat, cough, abdominal pain, diarrhea, travel, sick contacts, tick or mosquito bite, alcoholism or drug abuse. Family did report well controlled hypothyroidism, and influenza vaccination a week prior. Vitals signs: T: 37.5 C, HR: 98, BP:141/78, RR 17, Sp02 95% on RA. Examination revealed alert female, partially oriented to person, but not to time or place. She followed simple commands with mild delay. Nuchal rigidity, Jolt accentuation, Kernig’s and Brudzinski’s signs were negative. Cranial nerves 2-12 were intact, with normal motor and sensory examination. There was no rash or joints swelling. Laboratory data: WBC: 4.95 x109/L with 67% neutrophils, 19% lymphocytes, Hgb:134 g/L, PLT: 249 x 109/L Na141 mmol/L) K: 3.5 mmol/L, CO2 24 mmol/L, Urea 2.3 mmol/L, creatinine 51 µmol/L, glucose 6 mmol/L, calcium 2.34 mmol/L, INR: 1.0, TSH 2.1 mIU/L, normal liver function tests and ammonia level, and, negative urine drug screen. CT head without contrast, as well as CT angiogram head and neck were unremarkable. CSF analysis yielded 61 nucleated cells with 72% lymphocytes, protein: 1.02 g/L, and glucose: 4.3 mmol/l. Patient was placed on an empiric acyclovir, vancomycin, and ceftriaxone. Meningitis & encephalitis PCR panel was negative. Subsequently, an MRI brain showed no evidence of meningeal enhancement, or white matter disease. Electroencephalogram (EEG) revealed intermittent slowing with no epileptiform discharges. CSF fluid cultures showed no growth. Empiric regimen was discontinued on day 2, and patient completely recovered to baseline by day 3 of hospitalization. Our final diagnosis was post-influenza vaccination encephalopathy, as detailed below.

Discussion: The influenza vaccine is generally safe and effective. Adverse neurologic events have been reported post influenza immunization, as after other vaccines like smallpox, DPT and MMR. The incidence is very low (1 to 2 per million vaccinations) and symptoms usually begin within 4 weeks. Neurological insult can range in severity and type, including Guillain-Barre syndrome (GBS), Acute demyelinating Encephalomyelitis (ADEM), transverse myelitis, and a nonspecific meningoencephalitis syndrome. Hospitalist encounter encephalopathy in all its forms; infectious, inflammatory, metabolic, toxic, autoimmune and more; another consideration to the list is post-vaccine encephalopathy. Detailed history and examination, comprehensive investigations including metabolic, infectious and inflammatory markers, CSF analysis, CT and MRI imaging of the head with or without angiogram, EEG and further specialized testing is required on case-to-case basis. The diagnosis of post vaccine encephalomyelitis in our case was supported by exclusion, clinical presentation with lack of classic meningeal signs, recent influenza vaccination, mild lymphocytic pleocytosis, negative CSF PCR panel and cultures, normal MRI brain and spontaneous resolution of symptoms. Treatment is largely supportive and most patients recover spontaneously.

Conclusions: Post influenza vaccine meningoencephalitis is rare and a diagnosis of exclusion; though in the differential of encephalopathy, a commonly encountered diagnosis. Importantly, the rare occurrence of neurologic complications after influenza vaccination should not discourage its use, as efficacy surpasses the risks.