Background. Serum tryptase levels (sTL) are thought to reflect the individual burden of mast cells (MC). In patients with normal sTL, there is evidence for a decline over time of tryptase concentration during long-term immunotherapy (IT) for Hymenoptera venom allergy (HVA). Little is known about sTL changes over time in patients with mastocytosis. Aims and Methods. To analyze the sTL individual variations in patients with Indolent Systemic Mastocyosis (ISM) we retrospectively evaluated the registry of our Multidisciplinary Mastocytosis Outpatient Clinic. Patients with at least three consecutive measurement of sTL and a minimum follow-up of 24 months were included in the analysis. Changes of sTL over time were calculated as a linear regression analysis and the individual slopes were determined. Results. Ninety-two patients were studied. They were equally distributed by gender (M/F=52/40), median age at first observation was 50 years (range 19-80), median follow-up was 45 months (range 24-80). Half of the patients (n=46) had a diagnosis of ISM without skin lesions (ISMs-) and the other half (n=46) had ISM with skin lesions (ISMs+).ISMs- were referred for severe HVA (n=44), anaphylaxis after food (n=1) or severe osteoporosis (n=1). ISMs+ were referred for skin lesions only (n=28) or skin lesions associated with HVA (n=16), anaphylaxis after drug (n=1) or severe osteoporosis (n=1). sTL at first observation were 27.5±19.6 and 59.6±56.0 for ISMs- and ISMs+ patients, respectively. Overall, mean sTL tended to decline over time in ISMs-, while in ISMs+ there was a progressive increase (Figure 1). Means of individual slopes were significantly different in ISMs- (-0.51±4.71) vs ISMs+ (+2.91±10.2, p=.043). After diagnosis of ISM, 52 patients with severe HVA underwent long-term IT (39 ISMs- and 13 ISMs+). sTL values during IT tended to decline (mean of individual slopes was -0.35±4.32) but the difference was not significant vs patients not undergoing long-term IT (+2.76±10.77, p=.092). In 2 patients a rapid increase of sTL over 100 ng/mL during the follow-up accompanied the diagnosis of other non-MC hematologic malignancies.Conclusions. sTL changes over time are significantly different in ISMs- and ISMs+ patients. This could in part reflect the reduction of MC burden during long-term IT for HVA. However, it is likely that, as reported by others, ISMs- and ISMs+ represent separate biologic entities, arising from neoplastic MC with a different potential of evolution.
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