Chronic recurrent multifocal osteomyelitis (CRMO)

Clinical History

The patient presented with continuous pain in the left hip, which had been treated with physiotherapy for about 2 years. CRP was 4.2 mg/dl, other haematologic or biochemical parameters were normal. No skin rashes had been present. On external radiographs of the left hip, a "bone tumour" had been reported (images unavailable).

Imaging Findings

An MRI of the pelvis showed T2 hyperintense and T1 hypointense signal alterations in the left proximal femur, and to a lesser extent, in the 5th lumbar vertebra (Fig. 1a). The dorsal femoral trochanteric region and neck appeared thickened with unsharp borders. After contrast administration, there was intense patchy enhancement without demarcation of liquid zones (Fig. 1b). Soft-tissue oedema, but no mass could be seen in the neighbourhood. CT showed cortical bone thickening with irregular contours and multiple, partly confluent osteolytic foci (Fig. 2). A bone scintigram showed increased blood pool activity and late radionuclide deposition in both known regions, and revealed a third lesion in the corpus sterni (Fig. 3). A biopsy of the distal trochanteric region was obtained and showed a highly vascularised, predominantly inflammatory process with bone resorption and apposition. Malignancy could be excluded. Molecular biologic studies and cultures were negative for bacteria. The diagnosis of CRMO was established.

Discussion

CRMO is an inflammatory condition involving one or, more typically, multiple bones. It has been first described in the early nineteen-seventies and predominantly affects children and adolescents. Occurrence in adults is however not unknown. There seems to be a female predilection of 2:1 [1]. The aetiology of CRMO has not been fully explained. An association with autoimmune diseases, e.g. Crohn's or psoriasis has been well documented. Newer studies have postulated a genetic component suggesting interleukin-1 as a key factor in the pathogenesis [2]. There is also a close link with the SAPHO syndrome, a variety of hyperostotic skeletal disorders occurring together with synovitis and dermatoses, such as acne or pustulosis. By some authors, SAPHO is regarded as the adult form of CRMO and vice versa [3].
The onset of clinical symptoms is often insidious and there may be exacerbations and remissions. Fever is present in only half of cases, laboratory tests may be normal, and pain is typically localised, even in multifocal disease. The three most common sites at initial presentation are the lower extremities, the spine and the pelvis. As in SAPHO, the bones of the anterior thoracic wall (clavicles, sternum, ribs) can also be affected [1].
The radiographic and histopathologic features of CRMO are similar to chronic infectious osteomyelitis, often with predominant sclerosis in long-standing cases, but large abscesses, fistulous tracts and sequesters are usually absent. No pathogens can be isolated from the affected tissues (abacterial osteomyelitis). Biopsy must always be performed, for there is a broad differential diagnosis to the imaging appearance, which also includes malignant disease (see below). Radionuclide bone scans are traditionally prescribed to determine the extent of the disease [4]. In recent times, MRI is increasingly used for this purpose [5]. MRI is also the most suitable imaging study to monitor disease activity during and after treatment [1].
CRMO is generally a self-limited disease, however up to 50% of patients may experience skeletal growth disturbances or deformities later in life. The treatment is not standardised. Though antibiotics have no impact on the course of the disease, a trial treatment is sometimes necessary. In abacterial osteomyelitis, NSAIDs are the mainstay of treatment. Bisphosphonates and TNFa antagonists are used in more severe forms [3]. In the present case, the patient didn't respond well to NSAIDs and was treated with etoricoxib and a single dose of bisphosphonates. Fig. 4 shows an MRI of the pelvis obtained 2 years after the initial diagnosis.

Differential Diagnosis List

Final Diagnosis

Chronic recurrent multifocal osteomyelitis (CRMO)

URL:	https://www.eurorad.org/case/10036
DOI:	10.1594/EURORAD/CASE.10036
ISSN:	1563-4086