Serum Interleukin-6 Reflects Disease Severity and Osteoporosis in Mastocytosis Patients

<i>Background:</i> Systemic mastocytosis (SM) is a condition typically characterized by an increased number of mast cells in the bone marrow or in skin areas known as urticaria pigmentosa. Patients may present with flushing, itching, gastrointestinal symptoms, arrhythmias, headaches and osteoporosis. Some patients experience systemic symptoms indicative of SM in the absence of a positive bone marrow or skin biopsy, and are known as ‘clinical mastocytosis’, but are herein referred to as suspected of having systemic mastocytosis. Serum tryptase has been increasingly used as a biochemical marker of mastocytosis, but is not always elevated. <i>Objective:</i> To investigate the association of serum levels of two key mast cell mediators, interleukin-6 (IL-6) and tryptase, to each other and with disease severity in patients with mastocytosis. <i>Methods:</i> Patients responded to an announcement from the Systemic Mastocytosis Society (USA) and submitted frozen serum samples, but the precise diagnosis made by their own health providers was not known until after the assays were completed. There were 9 suspected systemic mastocytosis (SuSM), 3 cutaneous mastocytosis (CM), 11 indolent systemic mastocytosis (ISM), and 3 aggressive systemic mastocytosis (ASM). Five normal volunteers (3 females/2 males) also submitted samples, as did 33 cardiac patients without coronary artery disease. For 2 days prior to and during the collection period, mastocytosis patients were asked to abstain from any over-the-counter or food products containing biogenic amines, as well as drugs prescribed for this condition. Serum levels of IL-6 and tryptase were measured using established assays. <i>Results: </i>Twenty-six patients (14 females/12 males) submitted serum samples. There were 9 cases of SuSM (6 females/3 males) in whom tryptase values were borderline normal; IL-6 values were slightly elevated with one being high. In 3 cases of CM (2 females/1 male), both tryptase and IL-6 were slightly elevated. In patients with ISM (5 females/6 males), only 6/11 had any tryptase elevated significantly as compared to 9/11 with elevated serum IL-6. Three patients with ASM had significant elevations of both IL-6 and tryptase. The most consistent finding was that of IL-6 elevations in 7/7 patients (3 females/4 males) who reported symptoms of osteoporosis and/or bone pain (1 SuSM, 3 ISM, 3 ASM) in the absence of any coexisting condition involving bone pathology. <i>Conclusion:</i> Serum IL-6 is elevated in mastocytosis patients and correlates with severity of symptoms and the presence of osteoporosis. High serum IL-6 may not only signify disease progression, but may also participate in the pathophysiology of mastocytosis.