Working Diagnosis:
Osteoid osteoma of the right proximal humeral shaft.

Treatment:
She was referred to interventional radiology to discuss ablation of the osteoid osteoma. She continued physical therapy with progressive loading of the right upper extremity. She continued to use non-steroidal anti-inflammatory medications as needed for pain.

Outcome:
She declined ablation and continued with supportive care as her symptoms had started to improve. She completed physical therapy with progressive loading and successful return to body weight exercises. She no longer has pain with daily activities though has not been able to resume traveling rings or rock climbing yet.

Author's Comments:
The initial MRI ordered was concerning for a grade 3 humeral shaft bone stress injury. She had known risk factors for a bone stress injury including a history of restricted eating and irregular menses. Given ongoing nighttime pain despite four weeks of rest and the unusual location for a bone stress injury, a repeat MRI with and without contrast was ordered four months after the initial MRI. The repeat MRI raised concern for an underlying fracture or an osteoid osteoma. A CT scan confirmed the presence of an osteoid osteoma.

Osteoid osteomas were first described by Jaffe in 1935 (1). They are a common benign bone tumor that are highly vascularized and innervated and typically cause nighttime pain in young adults (2). Pain is caused by the release of prostaglandins through COX-1 and COX-2, which explains the relief provided by NSAIDs (3).

Osteoid osteomas have a nidus with an osteoid matrix and surrounding corticoperiosteal thickening and bone edema (1,4). They naturally regress in 6-15 years or 2-3 years with NSAID use (5). Other treatments include surgical resection and ablation. Percutaneous thermal ablation has a success rate of 91% (6) while radiofrequency ablation has a success rate of 95% (7).

Editor's Comments:
Osteoid osteomas are benign bone-forming tumors with a small radiolucent nidus that are typically best seen on CT scan and known for their production of prostaglandins. These classically present in the second decade of life with the lower extremity thought to be the most affected area. Males are two to three times more often found to have these tumors compared to females. Therefore, this case represents an atypical presentation, but clinical suspicion should remain high for someone with night pain that is responding to non-steroidal anti-inflammatories and typically warrant further imaging if the nidus is not seen on plain radiographs.

References:
1. Jaffe HL. "OSTEOID-OSTEOMA": A BENIGN OSTEOBLASTIC TUMOR COMPOSED OF OSTEOID AND ATYPICAL BONE. Arch Surg. 1935;31(5):709–728. doi:10.1001/archsurg.1935.01180170034003.

2. Carneiro, B.C., Da Cruz, I.A.N., Ormond Filho, A.G. et al. Osteoid osteoma: the great mimicker. Insights Imaging 12, 32 (2021). https://doi.org/10.1186/s13244-021-00978-8.

3. Mungo, D.V., Zhang, X., O'Keefe, R.J., Rosier, R.N., Puzas, J.E. and Schwarz, E.M. (2002), COX‐1 and COX‐2 expression in osteoid osteomas. J. Orthop. Res., 20: 159-162. https://doi.org/10.1016/S0736-0266(01)00065-1.

4. Kransdorf MJ, Stull MA, Gilkey FW, Moser RP (1991) Osteoid osteoma. Radiographics11(4):671–696. https://doi.org/10.1148/radiographics.11.4.1887121

5. Boscainos PJ, Cousins GR, Kulshreshtha R, Oliver TB, Papagelopoulos PJ (2013) Osteoid osteoma. Orthopedics 36(10):792–800. https://doi.org/10.3928/01477447-20130920-10.

6. Lindquester, W.S., Crowley, J. & Hawkins, C.M. Percutaneous thermal ablation for treatment of osteoid osteoma: a systematic review and analysis. Skeletal Radiol 49, 1403–1411 (2020). https://doi.org/10.1007/s00256-020-03435-7.

7. Lanza E, Thouvenin Y, Viala P, Sconfienza LM, Poretti D, Cornalba G, et al. Osteoid osteoma treated by percutaneous thermal ablation: when do we fail? A systematic review and guidelines for future reporting. Cardiovasc Intervent Radiol. 2014;37(6):1530–9. DOI 10.1007/s00270-013-0815-8.

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