Teaching Case

A 12-year-old girl presented with painful left mandibular swelling (Fig.1). Dental pathology was excluded. Laboratory tests revealed ESR 50mm/h, CRP 0.46mg/dL, negative antinuclear antibodies and rheumatoid factor. Anti-inflammatory therapy was started with prompt response. Once suspended, similar pain appeared in other localisations. Mandibular branch biopsy suggested an inflammatory reparative process.

Maxillofacial CT showed the involvement of the left mandible, at the distal portion of the horizontal branch, the angle and the vertical branch. The lesion was characterised by cancellous bone lysis, periosteal thickening and cortical bone destruction (Fig. 2). Whole body magnetic resonance imaging, performed to rule out other lesions, showed signal alteration of the mandible branch and the related surrounding soft tissues (Fig. 3). In addition, multiple focal lesions in the coracoid process of the right scapula, left rib, 4th and 5th sacral vertebrae, left iliac wing and ileum ischium pubic branch, distal metaphysis of the fibula, tarsal scaphoid, cuboid, 3rd right metatarsus, and 4th left metatarsus were detected (Fig.4).

Chronic recurrent multifocal osteomyelitis is a rare non-infectious inflammatory bone disease of unknown origin, characterised by multiple areas of sterile bone inflammation which become periodically symptomatic with swelling and pain.
In most cases, CRMO affects children and adolescents, frequently females, with a peak age of onset of 8-14 years of age [1]. In our experience clavicle, sternum, tibia, pelvis and proximal femur are the sites most frequently affected. Most patients present one symptomatic site at onset while other multifocal lesions appear subsequently causing recurrent exacerbations.
CRMO is a diagnosis of exclusion based on clinical presentation, radiological data and a culture negative bone biopsy. Key diagnostic criteria include multifocal sterile bone lesions, recurrence of signs and symptoms for at least 6 months, and lack of an identifiable cause [2]. In most cases bone biopsy is needed to confirm the diagnosis.
Imaging studies include radiography as first line investigation, followed by whole body MRI and, in some centres, the whole-body-Tc-99m labelled methylene diphosphonate bone scintigraphy in order to find multiple lesions [3]. In particular, WBMRI is a radiation free imaging tool initially applied to neoplastic diseases which has recently gained an increasing role in paediatrics, especially within a rheumatologic diseases framework [4]. The sensitivity of MRI for osteomyelitis has been reported as being between 82% and 100%, and specificity between 75% and 96% [3]. MR imaging is useful to determine disease extension and for follow-up. During the active phase of the disease, MR imaging shows typical findings of marrow oedema, with a multifocal pattern, which appears hypointense on T1-weighted images and hyperintense on STIR sequences. Associated periostitis, soft tissue inflammation, and transphyseal disease can also be visualised on MR.
The differential diagnosis for CRMO include infection, neoplastic lesions, and trauma. Within neoplastic lesions, the most frequent differential should be made with Langerhans cell histiocytosis.
The treatment of CRMO is based on local experience, but NSAIDs remain first choice [5]. CRMO follow-up studies suggest good long-term clinical outcomes although a minority of cases undergo a prolonged disease course [1].
The peculiarity of our case concerns especially the unusual primary site which caused difficulty in the differential diagnosis with other neoplastic and non-neoplastic diseases. A prompt diagnosis is important to prevent repeated courses of antibiotics and biopsies.
Moreover, our study confirms the excellent sensitivity of WBMRI in detecting CRMO lesions characterised by bone marrow oedema and a multifocal pattern.