The key to this case is identifying the lucent bone lesions on the first x-ray and triggering investigation.

Multiple bone lesions give us a differential that includes CRMO, LCH and polyostotic fibrous dysplasia.

• CRMO the multiplicity of lesions would be appropriate, but the distribution is wrong.
• LCH is a possibility, but the bone involvement is monomelic and there is no spinal abnormality
• fibrous dysplasia (polyostotic) seems the most likely diagnosis on the imaging and was confirmed at biopsy.

Once the diagnosis of polyostotic fibrous dysplasia is made, consideration about whether there is other multisystem involvement should trigger further investigations, especially endocrine to exclude McCune Albright.