Hypereosinophilic syndrome with central nervous system involvement treated with anti-IL-5 therapy

Hypereosinophilic syndrome (HES) is a rare disorder characterized by a persistent eosinophilia with a multi-organ involvement including neurological manifestation. A 59-year-old man was referred from a neurosurgery unit with a spastic triparesis with predominant left side involvement, dissociated sensory loss to Th7, and metastasis-like lesions in a brain CT. MRI examination of the thoracic spine revealed an intraspinal T2-hyperintensive lesion with a subtle central gadolinium enhancement at Th4-Th8 level. MRI of the cervical spine showed a C1-Th1 long T2-hyperintensive lesion with a partial gadolinium enhancement and MRI of the brain revealed a large tumefactive T2-hyperintensive lesion in the right hemisphere. Blood tests showed an increased number of eosinophils (1790 cells/µl; 18.3%). Common causes of the eosinophilia were excluded. After corticosteroid treatment moderate neurological improvement was observed however in the brain MRI new T2-hyperintensive lesions were revealed. The patient was referred to the Department of Allergology and qualified for a treatment with mepolizumab, a monoclonal antibody against IL-5, with subsequent clinical and radiological improvement. To the best of our knowledge, this is the first case of hypereosinophilic syndrome with brain and spinal cord involvement treated with mepolizumab.