Post‐H1N1 vaccine acute disseminated encephalomyelitis

Acute disseminated encephalomyelitis (ADEM) is a rare autoimmune demyelinating disorder of the central nervous system (CNS) that affects mainly children. Typically it happens after an infection and rarely after vaccination, with compromise of the white matter of the brain and/or spinal cord, characterized by a rapid development of encephalopathy in combination with multifocal and extremely varied neurological deficits. Brain and spinal cord magnetic resonance imaging (MRI) show disseminated demyelization in the CNS. Cerebrospinal fluid (CSF) examination can demonstrate unspecific alterations. We report the case of a previously healthy 8-year-old boy, who had fever, headache and somnolence 12 days after the first dose of vaccine against influenza H1N1. There was no previous history of infection or other vaccines in the previous 30 days, as well as no evidence of ongoing influenza H1N1 infection. The CSF was a crystalline fluid with 45 leukocytes/μL with 100% monocytes, glucose 62 mg/dL, and proteins 27 mg/dL. No infectious pathogens were identified in the blood or in the CSF. The patient had clinical seizures controlled with i.v. diazepam, became aphasic, and developed left hemiparesis. Electroencephalogram indicated slowing background activity with multifocal spikes and one electrographic seizure, after which i.v. phenytoin was initiated. He was transferred to the intensive care unit (ICU) due to coma and necessity of mechanical ventilation and did not have metabolic abnormalities. He was discharged from ICU with residual neurologic deficits, such as aphasia, paresis of extrinsic ocular muscles and ataxia. Brain MRI was compatible with ADEM (Fig. 1). Spine MRI showed no lesion. I.v. methylprednisolone pulse therapy (30 mg/kg per day) was given for 5 days, followed by 4 weeks of oral prednisone (2 mg/kg per day). The patient was discharged from hospital after 30 days. During follow up, a complete remission of symptoms occurred. According to the World Health Organization, in 2009 approximately 40 countries started national campaigns of vaccination against influenza A. Nearly 80 million doses of H1N1 vaccine were distributed and 65 million people were vaccinated. In this sense, rigorous surveillance of side-effects is necessary to establish the vaccine safety. ADEM usually occurs after unspecific viral upper respiratory airway infection. Only 5% are post-vaccine cases, more frequently after vaccination against measles, rubella and mumps. Only two case reports of ADEM after vaccine against H1N1 have been identified on publication database search. Obviously, vaccines are considered safe and provide one of the most cost-effective treatments. Vaccination campaigns have prevented thousands of deaths and disabling consequences, allowing the eradication of some diseases. In contrast, the worrying side-effects, although rare, must be promptly described in order to prevent undesirable events. Even recognizing that this is a description of a single case as well as that the causal association between this vaccine and the neurological alterations could not be totally proved, to our knowledge this paper represents the third description of a case of ADEM identified after H1N1 influenza vaccine. In the present case, early identification and treatment of ADEM were sufficient to ensure complete neurological recovery.