The IgG4-related disease is an immune-mediated multisystemic disorder, with nervous system involvement being increasingly recognized. 1,2 The most common manifestations are pachymeningitis, hypophysitis, and orbital disease.We report a 65-year-old man with no relevant past medical history (namely allergies). By the age 39 (1984), he developed a progressive gait instability and weakness in the lower limbs. Cerebrospinal fluid (CSF) showed 5 lymphocytes and proteins of 0.65 g/dL. Multiple sclerosis was considered as the cause of cerebellar and pyramidal syndromes, and the patient received adrenocorticotropic hormone for 3 days. He achieved a gradual and almost complete recovery and eventually lost to follow-up.In 2008, at age 54, he developed weakness in the lower limbs associated with urinary retention. The neurological examination revealed paraparesis and bilateral pyramidal syndrome, accompanied by urinary retention, superficial sensory loss (T4-level), and hypopallesthesia. The brain MRI revealed frontal parasagittal clastic lesions secondary to a previous car accident. Spinal MRI (Figure 1) documented a longitudinal extensive transverse myelitis (LETM).CSF analysis revealed pleocytosis-88 lymphocytes/μL, 38 eosinophils/μL-and elevated proteins (0.82 g/dL), with absent oligoclonal bands. Blood analysis was relevant for eosinophilia (0.64 × 10 3 /μL), elevated IgE (370 U/mL), and IgG4 231 mg/dL (>2 times above the upper limit of normal). Anti-aquaporin-4 (AQP4) and anti-myelin oligodendrocyte glycoprotein (MOG) antibodies were persistently negative on live cell-based assays. Parasitological and serological analysis were unremarkable. The immune study was otherwise normal, and he had no systemic auto-immune disorder. A full-body CT revealed mediastinal lymphadenopathies. He was treated with high-dose methylprednisolone for 5 days and maintained on oral