Among the thousands of signs and symptoms in the field of medicine, there is one that every doctor and medical student knows since the development of medicine. Clubbing is an easily noticeable sign in a patient’s fingers that can have wide implications on their health.
Clubbing is essentially when the angle (gap) between the fingernail bed and finger disappears. The formal definition is much more complicated, such as “the loss of the normal <165° angle, or Lovibond angle between the nailbed and the fold”, but for all intents and purposes the simple definition is sufficient.
To see if a patient has clubbing, the physician carefully studies the fingers against light. There are a few ways to check for clubbing but the most popular methods are holding the fingers out straight and holding them parallel to the ground, checking the angle between the nailbed and finger, or the Schamroth’s window test. The latter test is done by holding two opposing fingers (such as the left and right index fingers) against each other nail to nail. The fingers are then held against the light so that the light can shine through the “window” that is made. If the window is not seen, the test is positive and the patient has clubbing.
What does clubbing suggest? Clubbing was first noticed by Hippocrates, the father of Western medicine, who observed that people with clubbing tended to grab their chest and fall dead. This is one of the most common associations to clubbing – a congenital cyanotic heart defect such as tetralogy of Fallot or patent ductus arteriosus. Other common associations are related to the lungs, such as lung cancer (one of the most common causes) and various other lung diseases such as interstitial lung disease, tuberculosis and other chronic infections. There are also a myriad of other diseases associated to clubbing, including but not limited to: Crohn’s disease, ulcerative colitis, cirrhosis, celiac disease, Graves disease and certain types of cancers (lung, gastrointestinal and Hodgkin’s lymphoma mainly). Clubbing can also be idiopathic, where there is no apparent cause for the clubbing and the person just has it (possibly just born with it).
Despite knowing about clubbing for over 2000 years, we still do not know the exact reasons for clubbing. There are theories that it is related to a fall in blood oxygen content leading to vasodilation in the peripheries. As the pathophysiology is not clear and so many diseases are associated with it, when clubbing is found in the patient the physician should investigate the related organ systems (heart, lungs, GI mainly) to narrow down the possible cause of it. As many of the causes (such as lung cancer) carry a rather morbid prognosis, it is quite important to notice whether the patient has clubbing when doing a physical examination.