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Deformity of the finger or toe nails associated with a number of diseases
Drumstick fingers, Hippocratic fingers, digital clubbing, watch-glass nails
The incidence of clubbing is unknown; it was present in about 1% of people admitted to an internal medicine unit of a hospital. Clubbing has been recognized as a sign of disease since the time of Hippocrates.
Clubbing is associated with
Lung cancer, mainly non-small-cell (54% of all cases), not seen frequently in small-cell lung cancer (< 5% of cases)
Nail clubbing is not specific to chronic obstructive pulmonary disease (COPD). Therefore, in patients with COPD and significant degrees of clubbing, a search for signs of bronchogenic carcinoma (or other causes of clubbing) might still be indicated.
A special form of clubbing is hypertrophic pulmonary osteoarthropathy (HPOA), 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 hypertrophic osteoarthropathy
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. Theories as to its cause include:
Overproduction of prostaglandin E2 by other tissues.
Increased entry of megakaryocytes into the systemic circulation. Under normal circumstances in healthy individuals, megakaryocytes that arise from the bone marrow are trapped in the pulmonary capillary bed and broken down before they enter the systemic circulation. It is thought that in disorders where there is right-to-left shunting or lung malignancy, the megakaryocytes can bypass the breakdown within the pulmonary circulation and enter the systemic circulation. They are then trapped within the capillary beds within the extremities, such as the digits, and release platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). PDGF and VEGF have growth promoting properties and cause connective tissue hypertrophy and capillary permeability.
Clubbing of the fingernail: The red line shows the outline of a clubbed nail.
When clubbing is observed, pseudoclubbing should be excluded before making the diagnosis. Associated conditions may be identified by taking a detailed medical history--particular attention is paid to lung, heart, and gastrointestinal conditions--and conducting a thorough clinical examination, which may disclose associated features relevant to the underlying diagnosis. Additional studies such as a chest X-ray and a chest CT-scan may reveal otherwise asymptomatic cardiopulmonary disease.
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.
Cyanotic nail beds
The exact frequency of clubbing in the population is not known. A 2008 study found clubbing in 1%, or 15 patients, of 1511 patients admitted to a department of internal medicine in Belgium. Of these, 40%, or 6 patients, turned out to have significant underlying disease of various causes, while 60%, or 9 patients, had no medical problems on further investigations and remained well over the subsequent year.
At least since the time of Hippocrates, clubbing has been recognized as a sign of disease. The phenomenon has been called "Hippocratic fingers".
^ abVandemergel X, Renneboog B (July 2008). "Prevalence, aetiologies and significance of clubbing in a department of general internal medicine". Eur. J. Intern. Med. 19 (5): 325-9. doi:10.1016/j.ejim.2007.05.015. PMID18549933.
^Shah K, Ferrara TM, Jan A, Umair M, Irfanullah, Khan S, Ahmad W, Spritz RA (August 2017). "Homozygous SLCO2A1 translation initiation codon mutation in a Pakistani family with recessive isolated congenital nail clubbing". Br. J. Dermatol. 177 (2): 546-548. doi:10.1111/bjd.15094. PMID27681482.
^ abUppal S, Diggle CP, Carr IM, et al. (June 2008). "Mutations in 15-hydroxyprostaglandin dehydrogenase cause primary hypertrophic osteoarthropathy". Nat. Genet. 40 (6): 789-93. doi:10.1038/ng.153. PMID18500342.