Flare response seen in therapy for osteomalacia.

We report an interesting case of osteomalacia in which flare response was seen during therapy. The first 99mTc-methylene diphosphonate bone scan showed increased bilateral and symmetric uptake in the ribs, clavicles and iliac bones. Thoracic CT showed symmetric radiolucent seams (Looser's zones) in both ribs, which were pathognomonic of osteomalacia. After initiation of therapy with vitamin D, the patient's subjective symptoms gradually were relieved. On a second bone scan 4 mo. after initiation of therapy, the hot spots in the ribs remained unchanged. Uptake in the bilateral clavicles had become more intense, and new hot spots were recognized in the right lower ribs and left tibia. A third bone scan after 10 mo. demonstrated an obvious decrease in the number and intensity of the hot spots. Increased uptakes in the second scan were thought to be a flare response caused by therapy.