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The patient was a 10-year-old girl with pain and swelling of the left clavicle. The physical examination was normal except swelling and tenderness of the left clavicular region. All the laboratory tests were in normal range (white blood cells=6.13×109/L, haemoglobin=128 g/L, platelet=409×109/L, Wright=negative and Coomb’s Wright=negative) except mildly elevated erythrocyte sedimentation rate (ESR=42 mm/hour) and C reactive protein (CRP=11 mg/L). Chest X-ray revealed the enlargement of the medial third of the left clavicle along with periosteal reaction (figure 1A). The imaging findings proposed osteomyelitis and/or Ewing sarcoma. Thus, the patient underwent left clavicle bone biopsy which showed fragments of bony trabecula with mixed inflammatory cells infiltration, fibrosis and new bone formation (figure 2). The histopathologic findings were in favour of osteomyelitis. Thus, the physicians started empirical antibiotic therapy and waited for tissue culture result. The tissue culture was negative and the patient’s symptoms did not improve even after a course of antibiotic therapy. The clavicular lesion progressed and extended laterally during several months (figure 1B). MRI showed hypointensity on T1-weighted images and hyperintensity on T2-weighted images at the left clavicle with periosteal reaction and adjacent soft-tissue hyperintensity (figure 1C,D). After a review of radiopathologic and laboratory findings by a multidisciplinary team, the final diagnosis of chronic non-bacterial osteomyelitis (CNO) was established. The patient underwent treatment with naproxen and methotrexate and the patient’s symptoms remitted gradually.
CNO is a rare autoinflammatory disorder of bone. It is also called chronic recurrent multifocal osteomyelitis especially when it is more extended and involves multiple osseous regions. CNO is a feature of several monogenic autoinflammatory disorders, such as PAPA (pyogenic arthritis, pyoderma gangrenosum and acne syndrome), DIRA (deficiency of interleukin-1 receptor antagonists) and Majeed syndrome (autoinflammatory bone disorder, dyserythropoietic anaemia and neutrophilic dermatosis). It can be also associated with other inflammatory conditions, such as inflammatory bowel disease, ankylosing spondylitis, psoriasis and acne.1 2 Cutaneous manifestations, such as acne and palmoplantar pustulosis, are more prevalent among adults and can happen in addition to synovitis, hyperostosis and osteitis (SAPHO syndrome). Thus, SAPHO can be considered as a differential diagnosis and/or a subgroup of multifocal CNO in adults with both joint and skin involvement.1
CNO usually occurs in children and adolescents with a female predilection. It manifests as warmth, pain and swelling of the affected bone with or without fever. Metaphyseal areas of long bones, pelvis, clavicle and vertebral column are the most common sites of involvement. Involvement of characteristic bones, such as clavicle and mandible, suggests the clinical diagnosis of CNO. Laboratory findings are subtle in CNO and may include mildly elevated white blood cells, ESR and CRP.1 2
Imaging plays an important role in the diagnosis of CNO and the exclusion of other differential diagnoses. Plain X-ray radiography shows radiolucent, osteolytic and sclerosing lesions. However, plain X-ray radiography may be normal in the early stages of the disease. MRI is helpful in the detection of oedema as the only sign of the early bone lesions before the lytic and sclerotic changes. When CNO develops completely, MRI typically demonstrates osseous cortical thickening, lytic and sclerotic bone lesions along with oedema.1–3
When the diagnosis of CNO remains unclear, a bone biopsy is recommended to exclude the important differential diagnoses, such as chronic infections (bacterial osteomyelitis and tuberculosis), haematologic malignancies (leukaemia and lymphoma) and primary or secondary bone tumours. Some of the authors also suggest a bone biopsy in patients with poor general conditions, significantly elevated inflammatory parameters (high white blood cells, ESR and CRP) and unifocal bone lesion especially in atypical places (eg, skull).1 2
Treatment strategies in CNO are empirical and mainly based on retrospective observational studies. Non-steroidal anti-inflammatory drugs (NSAIDs), such as naproxen, are the first choice for treatment of CNO. When clinical remission is not achieved by NSAIDs or when there is arthritis or spinal lesions, additional treatment, such as disease-modifying antirheumatic drugs (methotrexate or sulfasalazine), TNF-α inhibitors (adalimumab, etanercept or infliximab) and bisphosphonate (pamidronate or zoledronic acid), should be administrated.1 2 Although CNO has a relatively favourable outcome and usually responds well to anti-inflammatory drugs, it is really a chronic condition with disease-related sequelae especially in those with uncontrolled inflammatory activity and spinal involvement.4
Contributors HE: Involved in patient clinical management and drafting of the manuscript. MV and MS: Involved in pathology interpretation, image preparation and drafting of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Parental/guardian consent obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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