Background Osteoid osteoma (OO) is a rare benign bone tumor affecting children and young adults. It causes inflammatory pain, usually relieved by aspirin or non-steroidal anti-inflammatory drugs. Standard treatment relies on percutaneous tumoral destruction using laser photocoagulation or radiofrequency ablation. Successful rates at 6 and 24 months reach 96% and 94%, respectively. Recurrences occur preferentially when nidus is greater than 12mm, or when OO is technically hard-to-reach. Moreover, localizations close to neuronal tissue, articular cartilage, spine or extremities are associated with high risk of complications. The efficacy of bisphosphonates on benign or malignant tumors has been widely reported, but has not yet been assessed in OO.

Objectives To evaluate the efficacy of bisphosphonates in technically hard-to-reach OO and in recurrent OO after percutaneous or surgical treatment.

Methods From september 2011 to june 2013, bisphosphonate treatment was proposed as an alternate treatment to patients suffering from recurrent OO or from technically hard-to-reach OO. Treatment consisted of 4mg zoledronate infusion (0,05mg/kg for children), repeated monthly if needed. Clinical efficacy was assessed on pain relief (pain killer uptake, Visual Analogical Scale (VAS)) and antitumoral efficacy by computer tomography (CT) and magnetic resonance imaging (MRI).

Results 17 patients (12 men, 5 women) with symptomatic OO received bisphosphonate infusions. Four patients had recurrence after laser (n=2) or surgical (n=2) treatment. 13 patients had hard-to-reach OO. Mean age was 24.3 years (8-38). OO locations were: pedicule or posterior arch of cervical (n=2), thoracic (n=2), or lumbar (n=1) vertebra, sacrum (n=2), coccyx (n=1), acetabular bone (n=1), femoral neck (n=2), great trochanter (n=1), tibial diaphysis (n=1), fibular neck (n=1), and talus dome (n=1). Pain management relied on NSAID (n=4), or aspirin (n=7). Two patients were treated with tri-monthly 60 mg pamidronate infusions from 2001 to 2013, and received 9 infusions. 15 were treated with monthly 4mg zoledronate infusions: 3 patients were completely improved by only one infusion, 3 by 2 infusions, 8 by 3 infusions and one by 5 infusions. After 3 months, 12 patients reported dramatic pain relief, 3 of them were improved within the first month, and 3 within 6 months. Mean VAS dropped from 77.2±11.1 to 22.7±22.3 (p<0,001) after treatment. Bisphosphonate treatment failed in one case, and data was missing for one patient. CT was performed in 8 patients and showed partial (n=2) or complete (n=5) mineralization of the nidus. MRI was performed in 11 patients and showed partial (n=2) or complete (n=9) regression of bone oedema. There were no adverse effect except flu-like syndromes (n=4).

Conclusions In this small bicentric study, bisphosphonate infusions displayed clinical and anti-tumoral efficacies permitting pain release, partial or complete mineralization of the OO nidus, and regression of bone oedema. These results encouraged a large scale controlled trial.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.4725