Pattern of Bony Involvement in an Irish Cohort with Chronic Recurrent Multifocal Osteomyelitis

Background: Chronic recurrent multifocal osteomyelitis (CRMO) is an auto-inflammatory condition primarily affecting children with an estimated prevalence of 1 per 10⁶ (OMIM 259680). It is characterized by relapsing episodes of localized bone inflammation. Since 2006, 43 patients have been diagnosed with CRMO at the National Centre for Paediatric Rheumatology (NCPR).

Objectives: To describe the pattern of bone involvement in this cohort.

Methods: Retrospective chart review.

Results: The median age at diagnosis was 10.5 years (range 6.8-15.4 years) with a male-to-female ratio of 1:2.6. All patients underwent MRI imaging of the symptomatic region and 86% had whole body MRI performed. Bone biopsy was performed in 79% of patients with 17% requiring a repeat. Biopsy was indicated when one or more of the following circumstances occurred; diagnostic uncertainty following regional or whole body MRI, patient unable to receive contrast agent for MRI, or whole body MRI unavailable. The mean follow-up period was 5.05 years.

The distribution of 264 documented lesions was as follows: lower limb bones 46.2% (23.1% tibia, 10.6% femur), 23.1% axial skeleton primarily the vertebrae (17.8%), pelvic girdle 16%, shoulder girdle 6.8% (predominantly clavicular lesions), and upper limb lesions accounted for only 8%. Most patients (86%) had multifocal disease.

Conclusion: Long bones of the lower limb were most frequently affected which is in keeping with previous reports. The relatively high incidence of vertebral lesions is significant as these carry a risk of morbidity from vertebral collapse or fracture.