Optic neuritis in lung adenocarcinoma: A challenging diagnosis.

Optic neuritis with CRMP-5 IgG is a paraneoplastic inflammation of the optic nerve associated with lung cancer, mostly small-cell lung cancer. We present the case of a patient with lung adenocarcinoma who developed progressive bilateral visual loss a few months after immune-chemotherapy with pembrolizumab and after Covid-19 vaccination. Positive CRMP-5 IgG were detected in blood sample and complete work-up - including brain MRI - did not show any progression. High dose systemic corticoids were administered with transient improving, followed by intravenous immunoglobulins, methotrexate and rituximab but despite negativization of CRMP-5 IgG, the patient had a progressive visual loss.