Pachydermoperiostosis (PDP) is a form of primary hypertrophic osteoarthropathy (see this term), a rare hereditary disorder, and is characterized by digital clubbing, pachydermia and subperiosteal new bone formation associated with pain, polyarthritis, cutis verticis gyrata, seborrhea and hyperhidrosis. Three forms have been described: a complete form with pachydermia and periostitis, an incomplete form with evidence of bone abnormalities but lacking pachydermia, and a forme frusta with prominent pachydermia and minimal-to-absent skeletal changes.