Remitting Seronegative Symmetrical Synovitis With Subsequent IgA Hypergammaglobulinemia. A Case of Chronic Inflammation Causing Macroprolactinemia and a Misdiagnosis

Prolactin is a pituitary hormone that functions in breast development and milk production in women and also plays an important role in immunoregulation and human immune responses, including autoimmune diseases. Macroprolactin, known as “big-big prolactin”, is due to the presence of marked hyperprolactinemia associated with evidence of prolactin-Ig (typically IgG4 or less frequently IgA) circulating complexes. We describes a case of 51 year-old female, with more than a 4 year history of reported hyperprolcatinemia who was treated with Cabergoline 0.5 mg weekly. Prior to treatment, she reported menses every 30-40 days, but denied galactorrhea or symptoms of sellar mass effect. Our patient had mildly elevated prolactin levels of 40-50 ng/dl. Her Thyroid function test were within normal limits. Patient had two pituitary MRIs in 2017 and 2019 which did not show sellar abnormalities. Prior to cabergolibe initiation, she was diagnosed with RS3PE syndrome (Remitting seronegative symmetrical synovitis with pitting edema) due to bilateral swelling in the dorsum of her hands. She was found to have hypergammaglobulinemia which was related to IgA elevation from chronic inflammation. Further investigation showed actual bio-active monomeric prolactin level was normal (4.8 ng/dl) and macroprolactin elevation from hypergammagolbulinemia. Before diagnosing her paraproteinemia and her macroprolactin predominance, she had received years of dopamine agonist therapy which was discontinued after diagnosis. We report a novel association of IgA predominant hypergammaglobulinemia from a chronic rheumatologic condition, leading to a misdiagnosed hyperprolcatinemia. Care should be taken to determine monomeric Prolactin levels prior to treatment, specially when symptoms are equivocal and/or imaging studies are negative.