Chronic Recurrent Multifocal Osteomyelitis

Clinical History

An 8-year-old male presented with right hip pain. Right acetabular biopsy yielded no organisms or malignant cells but showed low grade inflammation without evidence of histiocytes. ESR was mildly elevated. The patient came back after 1 year complaining of neck pain. Emergency CT and MRI showed lytic lesion involving C1.

Imaging Findings

Pelvic radiograph showed an expansile lytic lesion involving the right ilium (Figure 1). CT was performed and revealed a mixed lytic and sclerotic lesion without an aggressive periosteal reaction or matrix calcifications. The subsequent MRI showed a 4.8 cm heterogeneous enhancing mass without a soft tissue component (Figure 2).

The biopsy ruled out malignancy and active infection and the patient was treated with and responded well to NSAIDS for the next 3 months while demonstrating progressive resolution on the follow up MRIs. He came back after 1 year with a new neck pain.

ER CT of the C-spine then revealed a new lytic lesion of the right lateral mass of C1 (Figure 3). Follow-up MRI of the cervical spine demonstrated a homogeneously enhancing mass involving the right lateral mass of C1 with surrounding soft tissue oedema. There was no abscess or associated soft tissue mass (Figure 4).

Discussion

Chronic recurrent multifocal osteomyelitis (CRMO) is a sterile inflammatory bone disorder that predominantly affects children and adolescents. It is thought to have an autoinflammatory or autoimmune aetiology with recent studies suggesting a genetic component, but the exact mechanism remains unclear. It is characterized by recurrent and multifocal non pyogenic inflammatory bone lesions.

CRMO occurs most commonly in young females (female:male ratio 2:1) and has a mean age of onset of 9.8 years old [1]. Although symptoms are unifocal in 20-30% of reported cases, patients typically present with multiple asymmetric foci of localized bone pain and associated soft tissue swelling. Fever is also occasionally reported. In recurrent or chronic cases, pustular eruption on the palms and soles have been documented [2]. Laboratory tests may reveal elevated inflammatory markers, such as ESR and CRP. Biopsy and histologic examination are important to rule out infectious osteomyelitis and malignant bone tumors such as Ewings sarcoma. In CRMO, the exam often reveals a mixture of inflammatory cells without organisms or malignant cells.

Lesions have been described throughout the skeleton, but the most common areas of involvement are the metaphyseal regions of tubular bones, which account for approximately 75% of all lesions [3]. Other commonly reported sites include the vertebrae, pelvis, mandible and clavicle. In multifocal disease, the pattern is symmetrical in approximately one-fourth of cases.

Radiographs of symptomatic areas will reveal osteolytic lesions in the early stages followed by progressive sclerosis. Further imaging with CT can more clearly demonstrate the extent of localized disease and MRI reveals bone marrow oedema that is T1 hypointense with contrast enhancement and T2 hyperintensity [4]. MR imaging may also demonstrate associated periostitis, soft-tissue inflammation, and transphyseal disease.

CRMO can closely mimic a malignant lesion such as Ewings sarcoma and histiocystosis. Histologic examination is important to rule out these possibilities since treatment for CRMO is usually less aggressive.

Differential Diagnosis List

Final Diagnosis

Chronic Recurrent Multifocal Osteomyelitis

URL:	https://www.eurorad.org/case/14157
DOI:	10.1594/EURORAD/CASE.14157
ISSN:	1563-4086