Progressive Fingertip and Toe Enlargement

A 31-year-old man presented with 10 years of progressive fingertip and toe enlargement and intermittent aches of his distal forearms and lower legs.

Physical exam was notable for digital clubbing, proximal nail fold hyperpigmentation, and forearm and lower leg tenderness of palpation.

Plain radiographs of the ankles showed increased periosteal bone formation at the distal tibia and fibula. Serum laboratory tests, echocardiogram, and a whole-body PET-CT were normal.

What is the most likely diagnosis?