Explanation:
Subperiosteal bone resorption along the radial aspect of the middle phalanges is the earliest and most characteristic radiographic finding in primary hyperparathyroidism. Excess PTH stimulates osteoclastic bone resorption, particularly affecting cortical bone. Other features include salt-and-pepper skull and distal clavicular resorption. References: Resnick & Kransdorf, Bone and Joint Imaging; Harrison’s Principles of Internal Medicine.