Erdheim-Chester disease: typical radiological bone features for a rare xanthogranulomatosis.

CLINICAL HISTORY A 55 year old man was admitted to the rheumatology department owing to inflammatory back pain (occurring at 4 00 am, not aggravated by movement) without sciatica, increasingly severe over two years and associated with asthenia and weight loss (10 kg). No abnormalities were found on physical examination, except for tenderness on palpation of the spinous processes of L5 and S1. There was no significant past medical history. Laboratory tests showed a mild inflammatory picture: erythrocyte sedimentation rate 25 mm/1st h (normal 5–15), C reactive protein 12 mg/l (normal 0–10), fibrinogen 5.1 g/l (normal 2–4). Protein electrophoresis, red and white blood cell count, glucose, renal, and liver function tests were normal. Chemical bone markers (urinary pyridinoline, alkaline phosphatase, osteocalcin, parathormone, 25-hydroxyvitamin D, serum calcium and phosphorus, and urinary calcium and phosphorus) were normal.