Hypertrophic osteoarthropathy.

Hypertrophic osteoarthropathy (HOA) is an orphan syndrome characterized by abnormal proliferation of the skin and osseous tissues at the distal parts of the extremities. The main clinical features are: a peculiar bulbous deformity of the tips of the digits conventionally described as "clubbing," periosteal proliferation of the tubular bones, and synovial effusions. In most instances, HOA develops a reaction to a severe internal illness, such as lung cancer, cyanotic heart disease, or liver cirrhosis. There is a subgroup of patients who do not have underlying pathology. Such cases are classified as having primary HOA. Digital clubbing is easy to recognize. Any patient with newly developed digital clubbing should undergo careful search for an underlying illness with special attention to intra-thoracic pathologies. Painful HOA is treated with non-steroidal anti-inflammatory medications. Vascular endothelial growth factor and prostaglandin E2 have been proposed as key bone proliferating mediators.