clubbing [ME, clubbe] , an abnormal enlargement of the distal phalanges with a flattening of the curvature of the nail margin at the cuticle, where the nail meets the cuticle. It usually is associated with cyanotic heart disease or advanced chronic pulmonary disease but sometimes occurs with biliary cirrhosis, colitis, chronic dysentery, thyrotoxicosis, and sickle cell anemia. Clubbing occurs in all the digits but is most easily seen in the fingers. Advanced clubbing is obvious, but early clubbing may be difficult to diagnose. Clubbing is present if the transverse diameter of the base of the fingernail is greater than the transverse diameter of the most distal joint of the digit. The nail base angle measures more than 160°. See also Schamroth window test.
