Xanthogranulomatous Osteomyelitis and Crohn’s Disease: A Possible Association?

A 20-year-old male presented with a 10-week history of abdominal pain, bloody diarrhea, and right-sided pelvic pain. Initial blood investigations showed a C-reactive protein level of 87 mg/L (normal < 10). Other routine blood investigations were within normal limits. Stool samples for culture, ova, cysts, parasites, and Clostridium difficile were normal. At colonoscopy, there was patchy erythema with loss of vascular pattern and aphthous ulcers from the rectum to the caecum; the terminal ileum was normal. Biopsies were consistent with Crohn’s disease (CD). The patient was treated with a tapering course of prednisolone and mesalazine, with resolution of the intestinal and pelvic symptoms. However, a few months later, the right-sided pelvic pain recurred. A computed tomographic enterography scan was performed, which showed a 21-mm lesion in the right pubic bone. In view of persistent, severe, and disabling abdominal pelvic pain, a repeat computed tomographic enterography was performed 3 months later, with the only abnormality being that the bony lesion had increased in size to 62 × 41 × 36 mm. This was centered around the right superior pubic ramus in a parasymphyseal location, with perforation affecting the superior pubic ramus. There was no sclerosis, extraosseous extension, or internal matrix mineralization. Pelvic magnetic resonance imaging (MRI) demonstrated low signal intensity on T1, heterogeneous signal intensity on STIR imaging, and avid enhancement with gadolinium (Fig. 1, 2). An isotope bone scan excluded other skeletal lesions. A computed tomography-guided biopsy showed a bone sample infiltrated by aggregates of histiocytes and foamy macrophages, including occasional giant cells and numerous plasma cells, with some rare cholesterol clefts. Some lymphocytes were seen in the background with no evidence of infection (Fig. 3, 4). This was consistent with xanthogranulomatous osteomyelitis (XO). Tissue culture did not yield any bacterial