Plasmacytosis is a common immune signature in patients with MMN and CIDP and responds to treatment with IVIg

B cells and antibodies are thought to be relevant in chronic immune neuropathies (CIN). We analysed peripheral B-cell homeostasis and effects of high-dose intravenous immunoglobulin (IVIg) on B-cell phenotypes in patients with multifocal motor neuropathy (n = 22) and chronic inflammatory demyelinating polyneuropathy (n = 8) by multi-color flow cytometry. At baseline, total B-cell numbers were decreased, but mature plasma cells were markedly elevated. IVIg rapidly prompted a decrease in plasma cell numbers and left B-cell homeostasis unchanged. Thus, expanded frequencies of plasma cells might be involved in CIN immunopathogenesis and are downscaled after clinically successful IVIg administration.