What is an osteoid osteoma?
An osteoid osteoma is a benign bone tumour that usually occurs in adolescents and young adults. It typically occurs along the long bones of the limbs but it can happen in any part of the body. In fact, an osteoid osteoma is the most likely cause for children to present with a painful scoliosis (curvature of the spine).
Osteoid osteomas are usually small, solitary lesions that typically measure no more than 1.5cm in diameter. They are made up of a central nidus ("nest") of reactive woven bone surrounded by fibrovascular tissue and a zone of reactive bone. It isn't exactly clear why they develop, but the most popular theory is that they arise from abnormal cell growth.
What are the symptoms of an osteoid osteoma?
Osteoid osteomas are typically painful. They can cause a continuous dull ache at rest that progressively worsens over time.
Pain from an osteoid osteoma is usually at its worst at night but responds very well to oral nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or a salicylate medication like aspirin. This characteristic is so typical of osteoid osteoma, that the diagnosis can almost be made with this knowledge alone with imaging only needed for confirmation.
Why do osteoid osteomas hurt particularly at night?
Osteoid osteomas cause a localized increase in levels of the inflammatory mediators known as prostaglandins, particularly prostaglandin E 2 (PGE2). PGE2 is a powerful mediator for inflammation that has proven to be instrumental in the generation of pain symptoms from inflammatory and neuropathic disorders. When you take an anti-inflammatory medication, such as aspirin or an NSAID, you are preventing the production of these inflammatory mediator molecules, which explains why the drugs are so effective at stopping the pain associated with the condition.
But why is the pain worse at nighttime? We still don't understand why we experience severe nighttime pain with osteoid osteoma, but in an earlier post, we looked at some ideas that might explain the phenomenon.
How do you diagnose an osteoid osteoma?
As we heard earlier, some features of osteoid osteoma are so distinct that when heard in the context of the right patient your doctor can quickly come to a diagnosis. They should have a pretty good idea of the problem after taking your medical history and carrying out a physical examination. Only then is imaging used to confirm the diagnosis, location and size of the lesion.
- A CT scan remains the modality of choice for diagnosing an osteoid osteoma. Still, a keen eye may be able to spot the tell-tale features of a well-defined lytic (darker) area inside an area of hardened, sclerotic bone on an X-ray film.
- Magnetic Resonance Imaging (MRI) is helpful for identifying bone lesions but because an osteoid osteoma can resemble other bone conditions (why it's often referred to as the great mimicker) a CT scan is usually also done to confirm the diagnosis.
- If necessary, a biopsy is taken from the lesion for further examination. However, this is usually done at the time of treatment so don't worry, you won't need to undergo an additional procedure.
How is an osteoid osteoma treated?
- The pain associated with an osteoid osteoma usually responds well to nonsteroidal anti-inflammatory drugs (NSAIDs). For some patients regularly taking NSAIDs can cure osteoid osteoma. However, this may require several years of treatment.
Before you start taking any medication, even over-the-counter ones, check with your doctor to make sure it is safe for you to take them over a long period and get familiar with the potential side effects. More importantly, see your physician to confirm a diagnosis so that you do not mistake an osteoid osteoma for another condition with a potentially worse outcome.
- If you haven't responded to NSAIDs or you're unable to tolerate them for a long time, an invasive procedure may be necessary. The most common procedure used to treat osteoid osteomas is a CT-guided radiofrequency ablation treatment (RFA). This has a 95% success rate with one treatment.
- Other procedures include cryosurgery or open surgical excision with curettage.
Which technique gets used is usually determined by the location of the lesion.
Conclusion
Osteoid osteomas are a not-so-uncommon cause of bone pain. Because of the age group it mostly affects (children to young adults) it is often mistaken for "growing pains".
If you or someone you know is experiencing symptoms that sound like an osteoid osteoma it is important you arrange to see your doctor.
