An Overview of Nail Clubbing

It can happen so slowly, so gradually, that many people are unaware of the changes taking place in their fingernails until the new appearance jolts them into awareness.

It's a glum picture: The fingernails are curved downward, feel soft when pressed, and the tips are swollen.

They may see a dermatologist, who may conclude that there's nothing to worry about, particularly if nail clubbing runs in the family.

But nail clubbing could be a warning sign of a serious condition, too.

This article explains the symptoms and causes of nail clubbing. It also details how healthcare providers use tests to make a diagnosis.

Symptoms

Physical changes in the fingernails (or toenails) are the surest sign of nail clubbing. The nails become red, sponge-like, and swollen, almost like tiny balloons. This growth appears to occur from side to side as well as lengthwise.

The angle that normally exists between the nail bed and the nail becomes flat so that from close-up or a distance, the nails resemble upside-down spoons. These changes may occur alone or with other symptoms, such as shortness of breath or coughing.

Most often, clubbing occurs gradually. But the changes can occur rapidly, too.

Causes

Nail clubbing occurs from a buildup of tissue in the ends of the fingers (terminal phalanges). The nails become enlarged and curve downward. Why this happens is still largely a mystery to researchers.

It's thought that dilated blood vessels cause the fingers to swell, leading to the appearance of clubbing.

What is known is that the causes of clubbing fall into three categories:

Idiopathic: This is a category in which clubbing occurs for no obvious reason. It is unrelated to a medical issue; it just happens.

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, too.

Secondary clubbing: This refers to clubbing that occurs as a result of a medical condition. Conditions that are commonly associated with clubbing include:

• Lung cancer: This cancer accounts for about 90% of all clubbing cases, with nearly 30% of lung cancer patients experiencing clubbing. The deformity is more common among people with non-small cell lung cancer than small cell lung cancer.
• Other cancers: Hodgkin's lymphoma often triggers clubbing.
• Lung conditions: Some lung conditions linked to clubbing include bronchiectasis, idiopathic pulmonary fibrosis, empyema, pulmonary tuberculosis, and cystic fibrosis.
• Congenital heart disease: Heart disease that is present from birth, especially cyanotic heart disease (a defect), often leads to clubbing.
• Endocrine problems: Hyperthyroidism, especially Graves' disease, may be accompanied by clubbing.
• Gastrointestinal conditions: People with celiac disease (a chronic disorder of the digestive tract), cirrhosis, Crohn's disease, and ulcerative colitis may develop clubbing.

Diagnosis

Clubbing is often easy to diagnose based on a visual exam alone. But a healthcare provider may do other measurements to confirm the diagnosis:

• Distal/interphalangeal depth ratio, which basically measures a finger's depth between the skin and nail bed
• Lovibond angle, which focuses on the angle between the base of the nail and the nail
• Schamroth sign, which is the lack of a "window" (gap) between the fingers when the digits from each hand are placed together and the tops of both hands are touching.

A healthcare provider with experience in nail clubbing can be an invaluable resource. Chronic kidney disease and other disorders such as systemic sclerosis may cause finger changes that mimic the appearance of digital clubbing.

Diagnostic Tests for Causes of Clubbing

If your healthcare provider decides you have clubbing, their first move will be to ask about your family history. They'll be interested to know if it's a hereditary trait.

The provider will then do a careful history and physical exam, keeping in mind the possible causes associated with secondary clubbing. Depending on your symptoms, the tests may include:

• A chest X-ray and possibly a CT scan to look for lung cancer as well as other lung and heart-related conditions
• An electrocardiogram (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 tests

The next move, if any, will depend on what your healthcare provider discovers.

Treatment

There is no specific treatment plan for clubbing itself. The key is to find the underlying cause of the clubbing and treat it. Then the clubbing should go away on its own.

This may involve management by a specialist, depending on the cause. These could include pulmonologists, oncologists, infectious disease specialists, cardiologists, gastroenterologists, endocrinologists, and/or radiologists.

Summary

Nail clubbing causes the fingers (or toes) to swell and turn red while the nails turn downward. It could be just an inherited family trait or it could be a sign of a serious medical condition involving the heart, liver, lungs, intestine, or stomach. In fact, 90% of all clubbing cases are caused by lung cancer.

Pinpointing the cause of clubbing is important. Once the cause is treated, the clubbing should go away on its own.