Pseudogout attack induced during etidronate disodium therapy.

We report the first case of pseudogout attack in the distal interphalangeal (DIP) joints during etidronate disodium therapy. A 64-year-old woman had intermittent administration of etidronate disodium (Didronel; Sumitomo, Osaka, Japan) alone because of osteoporosis. Each cycle consisted of a daily dose of 200 mg for 2 weeks, repeating every 12 weeks. Two weeks after completing the third cycle, severe pain and swelling occurred in the DIP joints of the right middle, ring, and left ring finger; and skin ulcer formation was observed on the dorsal side of the DIP joints of the right middle and ring fingers as well as the left ring finger. Because monoclinic calcium pyrophosphate crystals were detected in the synovial fluid from the DIP joints of the right middle finger, we diagnosed these symptoms as induced by pseudogout attack. Oral loxoprofen sodium at a daily dose of 180 mg resulted in rapid symptom resolution. A decrease in function of calcium metabolism in elderly persons has been reported to be a cause of pseudogout attack. On the other hand, distal interphalangeal joint arthritis presenting as Heberden's nodes is a common condition in elderly patients. Therefore, pseudogout attack should be considered as an adverse drug reaction when administering bisphosphonate in elderly patients with Heberden's nodes.