Chronic recurrent multifocal osteomyelitis beginning with a solitary lesion of the ilium

Initial radiography demonstrated a mixed lytic and sclerotic lesion of the right ilium with extensive periosteal reaction, suggesting an aggressive process such as a neoplasm (Fig. 1). The MRI revealed that the right ilium was expanded with diffuse bone marrow edema and adjacent soft tissue edema within the iliacus and gluteus minimus muscles (Fig. 2). Findings were concerning for an infiltrative or malignant process, such as lymphoma, Ewing’s sarcoma or osteomyelitis. A CT scan demonstrated a markedly atypical periosteal proliferation involving the right ilium with a multifocal lytic lesion (Fig. 2). An open biopsy was subsequently performed followed by surgical bone curettage of right ilium. Histopathology showed a nonspecific fibro-inflammatory infiltrate composed of scattered chronic inflammatory cells including lymphocyte and plasma cells (Fig. 3). There was no evidence of neoplasm. Antibiotic therapy was started with intravenous ceftriaxone and clindamycin hydrochloride. After one week of antibiotic therapy, the patent’s clinical signs and symptoms resolved.

In July 2015, the patient was readmitted due to left upper arm pain and a mild fever. On physical examination, there was localized tenderness to the left arm. Full blood count was again normal. The CRP was 58.65 mg/L (normal value, ≤10 mg/L), and the ESR was 110 mm/h (normal value, 0-20 mm/h). Blood cultures were negative. The upper extremity MRI revealed a left humeral lesion with diffuse low T1 and intermediate to hyper intense T2 signal. There was no evidence of abscess formation in the surrounding soft tissue structures. CT revealed obvious cortical thickening of the left humerus (Fig. 4). A whole-body Technetium-99 m hydroxymethyl disphosphonate (Tc-99mHDP) bone scan was performed to investigate the possibility of multifocal lesions. It showed mild increased activity in the left humerus and obviously increased activity in the right ilium (Fig. 4). The bone biopsy of the left humerus revealed a non-specific fibro-inflammatory infiltrate and normal hematopoietic marrow without organism growth or evidence of neoplasm. Acid fast and KoH stains were negative. The flow cytometric analysis showed no evidence of a hematologic malignancy.

The biopsies of the lesions were notably negative for malignancy or infection. Based on the progressive nature of the patient’s clinical symptoms and imaging findings, she was diagnosed with CRMO. The treatment of CRMO generally involves anti-inflammatory agents targeting symptomatic relief, particularly non-steroidal anti-inflammatory medication (i.e. ibuprofen). The patient experienced relief with anti-inflammatory therapy and with local treatment of the right iliac lesion, leading support to the diagnosis.

CRMO has no specific clinical, imaging, or pathological findings. The diagnosis depends on a multidisciplinary effort. It is therefore important for skeletal radiologists to be familiar with the variable presentations of CRMO. This case demonstrates that CRMO can present as a solitary lesion of the ilium with significant periosteal proliferation and soft tissue changes. Knowledge of this unusual case may help skeletal radiologists to consider CRMO in their differential diagnosis.