Lymphocyte variant hypereosinophilic syndrome with severe eosinophilic pneumonia treated with mepolizumab: a case report

Lymphocyte variant hypereosinophilic syndrome (L-HES) is a rare disorder characterized by immunophenotypically abnormal T lymphocytes that produce excessive eosinophilopoietic cytokines, such as interleukin 5 (IL-5). Clinically, patients with L-HES can present with manifestations involving multiple organ systems, most commonly cutaneous lesions; however, isolated single-organ involvement excluding the skin is less common. The optimal treatment for L-HES remains poorly defined. Corticosteroids (CS) are often used as first-line therapy, while other agents – such as interferon  (IFN-), anti-IL-5 monoclonal antibodies, cyclosporine, and mycophenolate – are also employed in steroid- refractory cases, although no standardized treatment consensus has been established. Here, we report a rare case of L-HES presenting severe eosinophilic pneumonia (EP) as the sole manifestation. After experiencing relapses during treatment with CS and IFN-, the patient achieved a complete and favorable clinical response following initiation of low-dose mepolizumab – an anti-IL-5 monoclonal antibody – suggesting that mepolizumab may represent an effective therapeutic option for patients with L-HES complicated by EP.