Biconcave vertebral fractures as a possible distinctive feature of indolent systemic mastocytosis compared with primary osteoporosis

Summary: Indolent systemic mastocytosis (ISM) is a rare cause of skeletal fragility. In this study, patients with ISM showed a markedly higher prevalence of biconcave vertebral fractures compared with primary osteoporosis. Assessing fracture morphology may aid in differentiating ISM, reducing diagnostic delay, and guiding appropriate management. Purpose: Indolent systemic mastocytosis (ISM) is a rare disorder frequently associated with bone fragility and vertebral fractures (VFx). While the morphology of VFx has been studied in other metabolic bone diseases (e.g., osteomalacia), its role in ISM remains unclear. We aimed to evaluate the prevalence of specific VFx morphologies in ISM and assess their potential diagnostic value compared with primary osteoporosis (OP). Methods: We retrospectively enrolled adults with ISM and VFx, diagnosed according to WHO and ICC criteria. To increase statistical power, each ISM case was compared with two controls with OP. Clinical, densitometric, and laboratory data were collected. VFx were assessed on lateral spine X-rays (T4–L4) using Genant’s criteria and categorized as wedge or biconcave. Results: Sixty-six patients were included: 22 with ISM and 44 with OP. ISM patients were younger (68 ± 8 vs. 77 ± 7 years, p < 0.001) and more frequently male (32% vs. 7%, p = 0.043). ISM patients had more VFx (median 4 vs. 3, p = 0.039) and a higher proportion of biconcave VFx (80% vs. 22%, p < 0.001). ROC analysis showed high discriminatory power for the number and proportion of biconcave VFx (AUC 0.878 and AUC 0.919, respectively) in distinguishing ISM from OP, with optimal cut-offs of > 2 biconcave VFx or > 50% of total VFx. These findings remained consistent after adjustment for age and sex. Conclusion: Multiple biconcave VFx are significantly associated with ISM and may help differentiate it from primary OP. Assessment of fracture morphology could reduce diagnostic delay and guide appropriate management in patients with vertebral fragility fractures.