Subcutaneous IgG in immune-mediate diseases: proposed mechanisms of action and literature review

Intravenous immunoglobulin (IVIg) constitutes a relevant treatment option in various immune-mediated disorders, such as chronic inflammatory neuropathies and idiopathic inflammatory myopathies (IIM). Several advantages are linked to IVIg immunomodulatory and steroid sparing effects and to the possibility to withdraw the immunosuppressant therapy. However, the use of IVIg is not always easy to manage. It is associated with the need of an intravenous route of administration, high costs, and the risk of serious systemic adverse effects. More recently, the subcutaneous administration of immunoglobulin (SCIg) has been used in immunological practice as an alternative to IVIg, administered at lower dosages and more frequent intervals. This results in higher and more stable IgG serum levels and may prevent end-of-dose reduction and adverse effects caused by sudden IgG serum elevation. Moreover, the use of SCIg is more feasible, patient-friendly and cost-effective compared to the intravenous administration. In this context we compared IVIg and SCIg long term efficacy in the treatment of chronic inflammatory neuropathies and IIM, by reviewing the current literature and reporting the data obtained from our clinical experience about the use of SCIg in patients with myositis. We also described the most recent evidence on the immunomodulatory role of immunoglobulin, the pharmacokinetic properties of SCIg compared to the IVIg treatment, and the consequent clinical, laboratory and immunological implications.