IgG and kappa free light chain CSF/serum indices: evaluating intrathecal immunoglobulin production in HIV infection in comparison with multiple sclerosis

Objectives To study intrathecal kappa free light chain (KFLC) synthesis in people living with HIV (PLWH) in comparison with multiple sclerosis (MS). Methods Cross-sectional analysis including 56 untreated and 150 well treated PLWH, and compared with 58 controls, and 223 MS patients. Results Elevated serum/cerebrospinal fluid (CSF) IgG and KFLC indices were observed in untreated PLWH. Seventy percent of untreated PLWH had KFLC index above 6.1, a threshold associated with clinically isolated syndrome/MS diagnosis. No association was found between KFCL index and CSF markers of neuronal injury in either PLWH or MS patients. Conclusions HIV-related immune system dysfunction is often associated with an elevated KFLC index akin to those observed in MS. HIV infection should be considered as a differential diagnosis for patients presenting with neurological symptoms and increased intrathecal immunoglobulin synthesis.