An Overview of Nail Clubbing

Nail clubbing is a change in the structure of fingernails or toenails in which the finger and nail takes on the appearance of an upside-down spoon, and become red and sponge-like. It may occur alone or with other symptoms such as shortness of breath or coughing. There are a number of possible causes, including lung diseases, heart disease, and digestive tract conditions, though roughly 90 percent of cases are related to lung cancer. Clubbing may also be a normal, inherited trait. The diagnosis is made primarily through observing the fingers, and most commonly alerts a physician to order further studies such as a chest CT scan and more. The treatment will depend on the underlying cause of the clubbing.

Clubbing is medical condition first described by Hippocrates in which the fingers (and/or toes) have the appearance of upside-down spoons. It is caused by a build-up of tissue in the distant part of the fingers (terminal phalanges), that causes the end of the fingers to become enlarged and the nails to curve downward. In addition to a change in the angle of the nail and nail bed, the nails may become sponge-like and soft, and have a reddish discoloration. The "growth" in the digits appears to occur both laterally; from side to side, and longitudinally; lengthwise along the fingers.

The medical term used to describe clubbing is hypertrophic osteoarthropathy.

While many physicians think first of lung causes when they encounter people with nail clubbing, there are a number of potential causes. These fall into a few categories:

Idiopathic: This is a category in which clubbing occurs for no obvious reason, and is not of any concern medically: it just is. 

Inherited trait: There are a few ways that clubbing can be inherited. Most often the trait is inherited in an autosomal dominant fashion, meaning that if one of your parents carries the trait, there is a 50:50 chance that you will also inherit the trait.

Secondary clubbing: Secondary clubbing refers to clubbing that occurs in association with a medical condition. Conditions which are commonly associated with clubbing include:

• Lung cancer: Clubbing is a sign found in around 29 percent of people with lung cancer, and is the most common cause of clubbing (responsible for around 90 percent of cases). It is much more common with non-small cell lung cancer than with small cell lung cancer.
• Other cancers: Other cancers, especially Hodgkin's disease, may be present with clubbing.
• Lung conditions: Some lung conditions associated with clubbing include bronchiectasis, interstitial lung diseases such as idiopathic pulmonary fibrosis, empyema, pulmonary tuberculosis, and cystic fibrosis.
• Congenital heart disease: Heart disease that is present from birth, especially "cyanotic heart disease" such as tetralogy of Fallot, are frequently accompanied by clubbing.
• Gastrointestinal conditions: Some conditions in this category associated with clubbing include celiac sprue, cirrhosis, Crohn's disease, and ulcerative colitis.
• Endocrine problems: Hyperthyroidism, especially Grave's disease may be accompanied by clubbing.

The underlying process behind clubbing is still not understood. Scientists feel it may be related to platelet-derived growth factor and vascular endothelial growth factor although the precise mechanism is not known.

Clubbing most often comes on gradually, but may occur fairly rapidly for some people. For people with secondary clubbing, the symptom may go away after successful treatment of the underlying cause.

Nobody is quite certain why clubbing occurs, and there are probably several mechanisms. It's thought that for many people, dilation of blood vessels in the distant regions of the fingers results in the formation of connective tissue leading to the appearance of clubbing, but there are likely many different reasons for why this happens.

Most often, clubbing is noted on a physical exam and is expected based on other findings (such as the presence of lung disease or cancer).

Diagnosis: Clubbing is often obvious, but when subtle, other findings and measurements may be done to confirm the diagnosis. These include:

• Lovibond's profile sign: The angle between the base of the nail and the nail itself
• Distal/interphalangeal depth ratio
• Schamroth's sign: Lack of a window (gap) between the fingers, when the digits from each hand are placed together with the top of both hands touching.

Differential Diagnosis: Some rheumatoid conditions, such as reactive arthritis (Reiter's syndrome), can mimic the appearance of digital clubbing.

Diagnostic Tests When Clubbing Is Found: If your doctor notes you have clubbing, or if you bring up this concern to your doctor, the first thing she will do is ask you about your family history to determine if it may be a hereditary trait. She will then do a careful history and physical exam, keeping in mind the possible causes associated with secondary clubbing. Some tests, depending upon your symptoms, may include:

• A CT scan of your chest and/or other studies to look for lung cancer as well as other lung and heart-related conditions.
• An EKG and/or echocardiogram to evaluate your heart.
• Arterial blood gases and/or pulmonary function tests to evaluate your lung function and look for underlying lung diseases.
• Blood tests, such as liver function tests and thyroid function may be suggested.

There is no specific treatment, including surgical procedures for clubbing. Treatment of the underlying cause of clubbing can result in the resolution of clubbing for some people, for example, in people who have heart valve defects, clubbing may go away after successful surgery.