The exact cause for sporadic<unk>  is unknown. Theories as to its cause include: * Vasodilation (i.e., distended blood vessels). * Secretion of growth factors (e.g., platelet-derived growth factor and hepatocyte growth factor) from the lungs. * Overproduction of prostaglandin E2 by other tissues. * Increased entry of megakaryocytes into the systemic circulation. Under normal circumstances in healthy individuals, megakaryocytes that arise from the bone marrow are trapped in the pulmonary capillary bed and broken down before they enter the systemic circulation. It is thought that in disorders where there is right-to-left shunting or lung malignancy, the megakaryocytes can bypass the breakdown within the pulmonary circulation and enter the systemic circulation. They are then trapped within the capillary beds within the extremities, such as the digits, and release platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). PDGF and VEGF have growth promoting properties and cause connective tissue hypertrophy and capillary permeability.
Nail clubbing
Shell nail syndrome
Rose spots
Acrocyanosis
Brachymetatarsia
Parosmia
Copper beaten skull
Varicose veins