A 90-year-old male complains of hip and back pain. He has also developed headaches, hearing loss, and tinnitus. On physical exam the skull appears enlarged, with prominent superficial veins. There is marked kyphosis, and the bones of the leg appear deformed. Plasma alkaline phosphatase is elevated. A skull x-ray shows sharply demarcated lucencies in the frontal, parietal, and occipital bones. X-rays of the hip show thickening of the pelvic brim. The most likely diagnosis is

This patient has widespread Paget's disease of bone. Excessive resorption of bone is followed by replacement of normal marrow with dense, trabecular, disorganized bone. Hearing loss and tinnitus are due to direct involvement of the ossicles of the inner ear. Plasma alkaline phosphatase levels represent increased bone turnover. Neither myeloma or metastatic bone disease would result in bony deformity such as skull enlargement. Alkaline phosphatase is a marker of bone formation and does not rise in pure lytic lesions such as multiple myeloma.