Bone involvement in sarcoidosis: Insights from a multicentre Italian cohort

Background: Sarcoidosis is a multisystemic granulomatous disease that can involve the skeletal system, although bone manifestations are considered relatively uncommon and often underdiagnosed. Objectives: To describe the prevalence, clinical characteristics, and treatment outcomes of bone involvement in a large multicenter Italian cohort of patients with sarcoidosis. Methods: This retrospective, two-center observational study included 867 patients with histologically confirmed sarcoidosis followed at two Italian referral centers (2018-2025). Bone localization was identified by imaging (PET/CT, MRI, X-ray) and/or biopsy. Clinical, functional, laboratory, and therapeutic data were collected. Results: Bone involvement was found in 46 patients (5.3%), predominantly women (58.7%), with mean age at diagnosis of 49.7 ± 12.2 years. Osseous lesions were most frequently localized in the axial skeleton, particularly pelvis (54.3%) and vertebrae (52.2%). Bone sarcoidosis was significantly associated with extra-thoracic lymphadenopathy, hepatic, and splenic involvement (p < 0.001), reflecting a pattern of clustered multi-organ disease. Osteoporosis and osteopenia were present in 15.2% and 13.0% of cases, respectively. Corticosteroid monotherapy was the most common initial treatment (56.5%), while 30.4% received combination therapy with csDMARDs or biologics. At one-year PET/CT re-evaluation, 56.5% showed a reduction of SUV at bone sites, with no significant correlation between therapeutic regimen and metabolic response. Conclusions: Bone involvement in sarcoidosis, though relatively rare, represents a clinically relevant phenotype strongly associated with hepatosplenic and lymphatic disease and characterized by a preferential axial skeleton localization. Recognition of this pattern is essential for diagnosis and management. Given the retrospective design and the limited follow-up sample, these findings should be interpreted with caution. Close radiological monitoring and tailored therapeutic strategies are warranted to improve outcomes.