Denosumab Re-Challenge and Long-Term Efficacy for Aneurysmal Bone Cyst of the Spine: Enhanced Treatment Algorithm

Surgical treatment of aneurysmal bone cysts (ABCs) can be challenging, especially in the spine. Non-surgical treatments such as with denosumab have shown promising results in different osteolytic pathologies. This retrospective observational study aimed to evaluate the long-term clinical and radiologic response of patients with ABCs of the mobile spine treated with denosumab and propose an updated treatment algorithm. Six patients with relapsed and symptomatic ABCs of the mobile spine were treated with denosumab (120 mg subcutaneously on days 1, 8, 15, 29, and every 4 weeks thereafter) between 2012 and 2023. Disease assessments were conducted using CT and MRI at 3, 6, 9, and 12 months post-treatment. Clinical data, including pain levels, symptoms, and adverse events, were documented from patients' charts. Patients underwent an initial phase of treatment with denosumab, receiving a mean of 22 administrations (range 13-42) over a median follow-up period of 41 months (range 15-98 months). Clinical improvement was observed in all patients after 4 weeks of treatment, and all patients demonstrated a radiological response after 12-24 weeks on denosumab. Three patients were progression-free after discontinuing denosumab following 13, 15, and 42 administrations, respectively. At the last follow-up, after 38, 43, and 98 months, these patients remained stable without relapse of the disease. Three patients had a relapse of disease after denosumab; two of them underwent denosumab re-challenge, while one patient received one mesenchymal stem cells (MSCs) injection. All patients showed clinical and radiological improvement and were resulted to be disease-free at the last follow-up. This study demonstrates the long-term efficacy and safety of denosumab in treating ABCs of the mobile spine, as well as the potential of re-challenge in managing recurrence. A treatment algorithm is proposed, positioning denosumab as a viable therapeutic option after other local treatments. Careful patient selection, monitoring, and further research are necessary to optimize denosumab use for ABCs.