Child Neurology: Anti-Hu Encephalitis in an Adolescent With a Mediastinal Seminoma.

Anti-Hu antibodies are associated with autoimmune syndromes, mainly limbic encephalitis, encephalomyelitis, and painful sensory polyneuropathy (Denny-Brown). We report the case of a 15-year-old boy presenting with (EPC) found to have a right middle frontal gyrus brain lesion without atrophy or contralateral involvement. After partial resection, neuropathology revealed neuronal loss, reactive gliosis and astrocytosis, and perivascular mononuclear inflammatory infiltrate and features of neuronophagia resembling Rasmussen encephalitis. Suboptimal response to antiseizure drugs and surgery prompted further workup with identification of positive serum anti-Hu antibodies and a mediastinal seminoma. The patient was treated with immunotherapy including steroids, IV immunoglobulin, azathioprine, rituximab, plasmapheresis, and mediastinal lesion resection. However, he continued to experience EPC and psychomotor impairment along with left hemiparesis and dysarthria. Given clinical progression with failure to respond to immunotherapy and antiseizure polytherapy, hemispherotomy was attempted and seizure freedom achieved. A review of the literature found only 16 cases of neurologic presentations associated with anti-Hu antibodies in children, confirming the rarity of EPC in these cases. Thus, this report provides a new observation of germ cell mediastinal tumor associated with anti-Hu antibodies in children, broadening the spectrum of anti-Hu-associated neurologic disorders in children and highlighting the importance of considering antineuronal antibody testing in children presenting with EPC and brain lesions suggestive of Rasmussen encephalitis.