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Systemic Mastocytosis has been long identified as a potential cause of osteoporosis; nevertheless, data regarding longitudinal variation of bone mineral density (BMD) in patients with indolent systemic mastocytosis (ISM) are missing . We studied BMD variation at lumbar spine and proximal hip after 30-month (±6 months) follow-up in a large cohort of patients (83) with ISM without osteoporosis, supplementated with vitamin D and/or calcium when needed. We also analyzed the correlation between variation of BMD, basal serum tryptase levels and bone turnover markers (BTM). Sixty-four percent of our population was male; mean age was 52.1 (±11.5) years. Vitamin D insufficiency (serum levels of 25-OH-vitamin D, 25OHD, lower than 75 nmol/L) was found in more than 70 % of patients. After a follow-up of 30 ± 6 months with only vitamin D (5000-7500 IU weekly of oral cholecalciferol) or calcium (500 mg/die) supplementation when needed, we observed 2.1 % increase in BMD at lumbar spine, with no significant changes at hip. At the end of follow-up, almost 60 % of patients showed 25OHD serum levels still lower than recommended, despite vitamin D supplementation. Reduction in BMD after follow-up significantly correlated with high C-telopeptide of type I collagen serum levels at the time of diagnosis. In patients with ISM without osteoporosis, a routinary BMD evaluation within a time <2 years is not justified, except in the presence of elevated BTM. In these patients, vitamin D supplementation is frequently needed. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the therapeutic effect of denosumab, an anti-RANKL monoclonal antibody for the treatment of bone loss in indolent systemic mastocytosis (ISM) patients intolerant to bisphosphonates. Four patients underwent upon informed consent a treatment with denosumab 60 mg administered subcutaneously every 6 months with the same regimen used for postmenopausal osteoporosis. Bone mineral density (BMD) was measured at lumbar and femoral sites at baseline and after 1 year. C-terminal telopeptide of collagen type I (CTX), bone alkaline phosphatase (bALP) and tryptase serum level were determined at baseline and after 12 months with fasting blood samples withdrawals. BMD increased significantly at both sites during the 12 months; all the patients had an important decrease of serum CTX and of lesser extent of bALP serum levels. After denosumab treatment, a decrease in serum tryptase level was observed in all the patients. No adverse events or new fractures occurred. Denosumab seems to be a valid alternative for the treatment of bone loss in ISM. RANKL might be of key importance in the pathogenesis of ISM bone involvement.

Bone involvement, mainly osteoporosis but also osteosclerosis, is frequent in patients with indolent systemic mastocytosis (ISM). The recent characterization of the canonical Wnt/β-catenin pathway in the regulation of bone remodeling provided important insights for our understanding of the pathophysiology of a number of conditions. The regulation of Wnt pathway in bone is predominantly driven by the production of receptor inhibitors such as Dickkopf-1 (DKK1) and sclerostin (SOST). This study aimed to explore if the various bone involvements in patients with ISM might be explained by variations in serum levels of DKK1 and SOST. This is a cross-sectional study in an adult ISM cohort (13 men and 13 women with diagnosed ISM) and fifty-two healthy sex and age-matched controls. Early morning, fasting and venous sampling was obtained in all subjects. The main outcome measures were serum bone-specific alkaline phosphatase (bALP), C-terminal telopeptides of type I collagene (CTX), DKK1, SOST, parathyroid hormone (PTH), bone mineral density, and prevalent vertebral fractures. Mean DKK1 serum levels were about two-folds higher in patients, than in controls (65,0 ± 43.3 vs. 33.1 ± 19.4 pmol/L, respectively; p < 0.001), irrespective of the presence of osteoporotic or diffuse osteosclerotic bone involvement. DKK1 serum levels were positively correlated with PTH and both CTX and bALP. Mean SOST serum levels were not significantly different in patients versus controls, and we did not observe any significant correlation between SOST and any available clinical or laboratory parameters, with the only exception of a positive correlation with age. In conclusion, in our study, we observed that DKK1, but not SOST, serum levels significantly increased in ISM patients with various bone involvements, and correlated with PTH and bone turnover markers. Our results suggest that the Wnt/β-catenin pathway is not primarily involved in the pathophysiology of the array of bone involvement in ISM.

We have recently reported a long-lasting decrease in circulating γδ T cells in osteoporotic patients on oral amino-bisphosphonates (N-BPs). Here we verify whether these changes are associated with the occurrence of acute phase response (APR) to intravenous (IV) zoledronic acid (ZOL) or changes of other circulating white blood cells (WBC). WBC count was obtained before and 1 year after a single IV administration of 5 mg ZOL in 36 osteoporotic patients (mean age 72 ± 9, range 45-86 years) without other relevant diseases; 12 of 36 patients developed the classical APR. After 1 year in the patients who experienced an APR, but not in the others, a significant decrease not only of γδ T cells (-30 %), but also of total lymphocytes (-11 %) and eosinophils (-27 %), was observed. The mechanism leading to the observed decrease of circulating lymphocytes and eosinophils remains unclear, but our observation opens a new frontier for the understanding of the immunoeffects of N-BPs.

The aim of this study was to explore whether desensitization to the occurrence of the acute-phase response (APR) in patients previously treated with amino-bisphosphonates (N-BPs) is due to a long-lasting reduction in the number of circulating γδ T cells. Circulating lymphocyte subpopulation counts were obtained from 63 patients with postmenopausal or senile osteoporosis at baseline and after 2 days and 12 months of the first intravenous (IV) 5 mg zoledronic acid (ZOL) infusion. At baseline both the proportion and absolute number of circulating γδ T cells were significantly higher in patients who had never used N-BPs vs. previous users, either oral or IV. A typical APR was observed in none of the patients given IV ZOL a year earlier, in 6 (22 %) of the patients previously treated with oral N-BPs, and in 13 (57 %) of the patients naive to any N-BP treatment. In patients naive to N-BPs, a significant reduction in both total lymphocytes and their subsets was observed 2 days after ZOL infusion; all these changes returned to baseline values 1 year later with the exception of γδ T cells, which remained significantly lower in terms of both proportion and absolute number. These results indicate for the first time that both IV and oral N-BP treatments are associated with a long-lasting decrease in circulating γδ T cells, and this may explain the lower incidence of APR in patients previously exposed to N-BPs. Other clinical implications of this sustained effect of N-BPs on immune-regulatory cells might be important.