In medicine, nail clubbing (also known as drumstick fingers and watch-glass nails) is a deformity of the fingers and fingernails associated with a number of diseases, mostly of the heart and lungs.:656 Hippocrates was probably the first to document clubbing as a sign of disease, and the phenomenon is therefore occasionally called Hippocratic fingers.
Signs and symptoms 
Clubbing develops in five steps:
- Fluctuation and softening of the nail bed (increased ballotability)
- Loss of the normal <165° angle (Lovibond angle) between the nailbed and the fold (cuticula)
- Increased convexity of the nail fold
- Thickening of the whole distal (end part of the) finger (resembling a drumstick)
- Shiny aspect and striation of the nail and skin
Schamroth's test or Schamroth's window test (originally demonstrated by South African cardiologist Leo Schamroth on himself) is a popular test for clubbing. When the distal phalanges (bones nearest the fingertips) of corresponding fingers of opposite hands are directly opposed (place fingernails of same finger on opposite hands against each other, nail to nail), a small diamond-shaped "window" is normally apparent between the nailbeds. If this window is obliterated, the test is positive and clubbing is present.
When clubbing is encountered in patients, doctors will seek to identify its cause. They usually accomplish this by obtaining a medical history—particular attention is paid to lung, heart, and gastrointestinal conditions—and conducting a clinical examination, which may disclose associated features relevant to a diagnosis. Additional studies such as a chest X-ray and a chest CT-scan may also be performed.
Disease associations 
Although many diseases are associated with clubbing (particularly lung diseases), the reports are fairly anecdotal. Prospective studies of patients presenting with clubbing have not yet been performed, and hence there is no conclusive evidence of these associations.
Isolated clubbing 
Clubbing is associated with:
- Lung disease:
- Lung cancer, mainly non-small-cell (54% of all cases), not seen frequently in small-cell lung cancer (< 5% of cases)
- Interstitial lung disease
- Complicated tuberculosis
- Suppurative lung disease: lung abscess, empyema, bronchiectasis, cystic fibrosis
- Mesothelioma of the pleura
- Arteriovenous fistula or malformation
- Heart disease:
- Gastrointestinal and hepatobiliary:
Nail clubbing is not associated with chronic obstructive pulmonary disease (COPD). Therefore, in patients with COPD with significant degrees of clubbing, a search for signs of bronchogenic carcinoma (or other causes of clubbing) might be indicated.
A special form of clubbing is hypertrophic pulmonary osteoarthropathy, known in continental Europe as Pierre Marie-Bamberger syndrome. This is the combination of clubbing and thickening of periosteum (connective tissue lining of the bones) and synovium (lining of joints), and is often initially diagnosed as arthritis. It is commonly associated with lung cancer.
Primary HPOA 
Primary hypertrophic osteoarthropathy is HPOA without signs of pulmonary disease. This form has a hereditary component, although subtle cardiac abnormalities can occasionally be found. It is known eponymously as the Touraine-Solente-Golé syndrome. This condition has been linked to mutations in the gene on the fourth chromosome (4q33-q34) coding for the enzyme 15-hydroxyprostaglandin dehydrogenase (HPGD); this leads to decreased breakdown of prostaglandin E2 and elevated levels of this substance.
The exact cause for sporadic clubbing is unknown, with numerous theories as to its cause. Vasodilation (distended blood vessels), secretion of growth factors (such as platelet-derived growth factor and hepatocyte growth factor) from the lungs, and other mechanisms have been proposed. The discovery of disorders in the prostaglandin metabolism in primary osteoarthropathy has led to suggestions that overproduction of PGE2 by other tissues may be the causative factor for clubbing.
The exact frequency of clubbing in the population is not known. A 2008 study found clubbing in 1% of all patients admitted to a department of internal medicine. Of these, 40% turned out to have significant underlying disease of various causes, while 60% had no medical problems on further investigations and remained well over the subsequent year.
See also 
- Clubbed thumb (unrelated congenital deformity)
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