To report a case of H1N1 Associated Acute Disseminated Encephalomyelitis (ADEM) in an adult, with atypical MRI finding of leptomeningeal enhancement.

H1N1 largely affects individuals less than 24 years of age. Associated CNS symptoms in children include seizures, encephalitis, ADEM, and motor paralysis or sensory loss. ADEM typically presents with MRI findings of multiple T1-hypodense and T2-hyperintense bilateral asymmetric, supra- and infratentorial patchy lesions. There is currently no report in the literature of adult H1N1 associated ADEM presenting with leptomeningeal enhancement on neuroimaging.

We present a case of a 33-year-old female hospitalized for four days of shortness of breath that progressed to acute respiratory distress syndrome secondary to H1N1 infection. She was intubated, sedated, and treated early with antivirals. She initially underwent MRI Brain to investigate findings of bilateral papilledema, which showed diffuse leptomeningeal enhancement. CSF studies were not consistent with bacterial or viral meningitis. When sedation was withdrawn and encephalopathy improved, she was noted to have right hemiparesis. MRI Brain showed left greater than right T2 hyperintensities most prominently in the corona radiata with associated restricted diffusion. She was able to recover with physical therapy, without steroid treatment. Follow up imaging showed resolution of diffusion restriction and evolution of T2 white matter hyperintensities that were most consistent with ADEM.

MRI of the brain demonstrated sequence of findings from leptomeningeal enhancement at the early stages of H1N1 encephalopathy with further progression to ADEM.

We hypothesized that leptomeningeal enhancement could be an early MRI finding in the course of H1N1-CNS manifestation. This may be a result of breakdown of the blood-brain barrier early in the disease course. In-depth analysis with larger cohort studies are required to investigate whether these findings are useful in early diagnosis of ADEM in patients with H1N1.