A patient whose hat and denture are becoming too small has increasing head size. The most likely diagnosis is:

Correct answer: D. Paget's disease of bone

• A. Acromegaly (GH excess in adults) can also cause jaw enlargement (prognathism) and coarsening of facial features, but the pattern of hat becoming too small and dentures not fitting is CLASSIC Paget's.
• B. Fibrous dysplasia causes bony expansion but is typically diagnosed in younger patients and does not present with the Paget's pattern of progressive enlargement in older adults.
• C. Hyperthyroidism causes weight loss, tachycardia, and bone loss — not progressive skull/jaw enlargement.
• D. Correct. Paget's disease causes progressive enlargement of affected bones due to abnormal bone remodeling (excessive osteoclastic resorption followed by disorganized osteoblastic repair). Enlargement of the skull causes hats to no longer fit, and jaw enlargement causes dentures to become too small.