To the Editor.
—In a previous issue of the Archives, Treece et al1 reported the successful use of tetracycline hydrochloride for sclerosis of recurrent thyroid cysts with uniformly successful results.1 One of us wrote an accompanying editorial.2 Subsequently, it has been reported3 that the first known use of an agent (tincture of iodine) to sclerose a thyroid cyst was in 1861.4We have since used tetracycline for thyroid cyst sclerosis with salutary results in approximately 20 patients. However, on two occasions, we have each noted a patient who experienced extreme pain almost immediately in the area of injection that was relieved only by the administration of intravenous morphine sulfate or intramuscular meperidine hydrochloride. One patient had had several aspirations performed elsewhere with fluid reaccumulation. After she experienced the pain, she was examined almost immediately by ultrasound, which showed no residual cyst. Presumably, the tetracycline extravasated