Hyperviscosity Syndrome in Immunoglobulin G4 (IgG4)-Related Disease and the Use of Therapeutic Plasma Exchange: A Case Report.

Immunoglobulin G4 (IgG4)-related disease is a rare multi-system immune-mediated inflammatory condition. Pathologically, it is associated with an increase in plasma IgG4 levels and tissue infiltration of IgG4-secreting plasma cells of any organ. Clinical features vary, but it usually presents with the diffuse enlargement and dysfunction of the affected organ. IgG4-related disease leading to hyperviscosity syndrome from polyclonal hypergammaglobulinaemia has only been described in two case reports, and no consensus regarding the treatment of this organ- and life-threatening complication exists. We report the case of a 50-year-old man who was admitted with symptoms of hyperviscosity and an extremely elevated IgG4 level. A presumptive diagnosis of IgG4-related disease causing hyperviscosity syndrome was made. He underwent a therapeutic plasma exchange with a resolution of his symptoms. In view of the likely diagnosis of IgG4-related disease and only refractory improvements in IgG4 levels, immunosuppression with steroids and rituximab was commenced. This led to a sustained fall in IgG4 levels and remission. Hyperviscosity syndrome should be recognised as a complication of IgG4-related disease, and therapeutic plasma exchange can be employed in the emergency treatment of this life-threatening condition.