A distinction is to be made between simple clubbing of the fingers and osteoarthropathy. The primary change in the limbs of patients with pulmonary hypertrophic osteoarthropathy is an overgrowth of vascular connective tissue investing the structures in the distal part of the limb. The newly formed tissue lies over the periosteum and new bone formation takes place under it. Surrounding the joints the newly formed tissue gives the appearance of periarthritis, though there are no specific articular changes. When it invades the nail beds it gives rise to clubbing of the fingers. Osteoarthropathy is usually secondary to pulmonary disease, but it may be associated with thoracic lesions without pulmonary involvement. ment. The relevant factor may be disease of the pleura, with neural reflexes affect. ing the limbs.