Periosteal new bone formation and disseminated granulomatosis in a patient with Crohn's disease.

In a 20-year-old man, a proliferative periosteal new bone growth developed over the left forearm. Crohn's disease had been diagnosed the year before. Bone biopsy demonstrated granuloma formation. Biopsy specimens of skin lesions demonstrated granulomas as well. Bowel studies indicated active small intestinal inflammation with fistula formation. Despite the superficial resemblance to hypertrophic osteoarthropathy, it is believed that this case represents Crohn's disease with disseminated granulomatosis involving skin and periosteum.