Diagnostic value of IgG4 Indices in IgG4-Related Hypertrophic Pachymeningitis ★

• Diagnostic biomarkers for IgG4-Hypertrophic Pachymeningitis (IgG4-HP) are lacking
• Cerebrospinal fluid (CSF) analysis in IgG4-HP shows elevated IgG4 concentrations
• CSF IgG4 and IgG4 Indices are significantly higher in IgG4-HP than in other HP
• CSF IgG4 and IgG4 Indices represent valid alternatives to biopsy in diagnosing IgG4-HP

Diagnosis of IgG4-Related Hypertrophic Pachymeningitis (IgG4-HP) relies on meningeal biopsies, because cerebrospinal fluid (CSF) diagnostic biomarkers are lacking. Here, we determined whether IgG4 intrathecal production could distinguish IgG4-HP from other disorders presenting with HP (OHP). In patients with IgG4-HP, the median CSF IgG4 concentration, IgG4 Index and IgG4Loc were significantly higher than in both controls and OHP. CSF IgG4 levels higher than 2.27 mg/dL identified 100% of IgG4-HP and 5% of OHP. An IgG4Loc cut-off of 0.47 identified 100% of IgG4-HP and no cases of OHP. Our results support CSF IgG4 quantification and IgG4 Indices as alternatives to meningeal biopsy for the diagnosis of IgG4-HP when this procedure is contraindicated or uninformative.