Severe post-influenza (H1N1) encephalitis involving pulvinar nuclei in an adult patient

Abstract

Neurological complications of H1N1 infections are mostly found in children, but rare cases of acute encephalopathy and post-infectious encephalitis such as acute disseminated encephalomyelitis (ADEM) have been described in adults. We report a case of an adult presenting with a progressive and severe encephalopathy that developed after H1N1 respiratory infection resolution. Cerebrospinal fluid (CSF) analysis was normal, including negative PCR for herpes simplex virus, H1N1, influenza B and JC virus, and absent oligoclonal IgG bands in CSF and serum. Initial CT scan was normal, but later MRI showed posterior multifocal leucoencephalopathy with pulvinar sign. The delayed neurological findings together with the ancillary investigation, namely the MRI pattern with both grey and white matter involvement, raised the possibility of a post-infectious process, rather than an acute encephalitis. Despite aggressive immunotherapy, the patient experienced severe neurological sequelae. Early recognition of ADEM manifestations by those dealing with H1N1 infection is important as early immunotherapy may improve the prognosis.

Figure 1

Brain MRI showing intra-axial multiple lesions with hyperintense signal on fluid-attenuated inversion recovery/T2, involving both thalamic pulvinar nuclei, frontal and opercular subcortical regions bilaterally, the left temporoparieto-occipital cortex and the right medial temporo-occipital region with discrete overlying parietal involvement. Diffusion-weighted images showing restriction of diffusion of the involved areas.