Poster - Anti-NMDAR encephalitis in a patient with IgG4 related hypertrophic pachymeningitis : a case report.

IgG4-related hypertrophic pachymeningitis (IgG4-RHP) is a rare condition characterized by localized or diffuse inflammation due to significant thickening of the dura mater. It may coexist with autoimmune diseases and malignant or infectious diseases. Herein, we describe the first case of a patient showing IgG4-HP and anti-N- methyl-d-aspartate receptor (NMDAR) disease. A 67-year-old female was admitted to the emergency department (ED) of Pescara General Hospital for persistent speech difficulties that had lasted for more than two weeks. A brain Magnetic Resonance Imaging (MRI) showed diffuse T1-intense dural thickening with contrast enhancement. IgG subclass testing revealed elevated IgG4 concentrations in both serum and CSF. The serum immunoglobulin class examination found a high value of IgG4 (3.89 g/L; reference range: 0.08–1.40 g/L), whereas IgG1, IgG2, and IgG3 came back all normal. Immunoglobulin IgG subclass determination in the CSF revealed a higher IgG4 titre (83 mg/L) and undetectable values for all other IgG subclasses. CSF albumin level was 262 mg/L [normal range, 139–246 mg/L]. Isoelectrofocusing investigation showed intrathecal synthesis, while an indirect immunofluorescence cell-based assay (CBA) demonstrated the presence of NMDAR antibodies in the CSF. Consequently, the patients started a corticosteroid treatment and her clinical condition progressively improved. Clinical symptoms, high IgG4 levels in both the serum and cerebrospinal fluid, and the typical thickening of the dura mater observed in imaging investigations were all highly suggestive of IgG4-related pachymeningitis. However, further autoimmune laboratory investigations revealed the presence of anti-NMDAR in the CSF, suggesting the simultaneous coexistence of the anti-NMDAR encephalitis, a rare autoimmune condition that may cause subacute psychiatric symptoms such as psychosis, memory loss, movement disorders, and seizures. To the best of our knowledge, this is the first case described of the overlapping between IgG4-HP and anti-NMDAR conditions. The clinical aspects of this overlapping condition are not yet fully known, and a missed diagnosis of either disease may lead to suboptimal control of the patient's clinical course. Close collaboration among physicians, pathologists, and clinical pathologists is essential for the early diagnosis of both conditions.