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Nail clubbing, also known as digital clubbing or clubbing, is a deformity of the finger or toe nails associated with several diseases, anomalies and defects, some congenital, mostly of the heart and lungs. When it occurs together with joint effusions, joint pains, and abnormal skin and bone growth it is known as hypertrophic osteoarthropathy.

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Clubbing is associated with lung cancer, lung infections, interstitial lung disease, cystic fibrosis, or cardiovascular disease.

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Clubbing has been recognized as a sign of disease since the time of Hippocrates. It is seen in 1% of internal medicine admissions and is associated with serious underlying disease in 40% of these admissions.

Causes

Clubbing is associated with

  • Lung disease:
  • Lung cancer
  • Interstitial lung disease most commonly idiopathic pulmonary fibrosis
  • Complicated tuberculosis
  • Suppurative lung disease: lung abscess, empyema, bronchiectasis, cystic fibrosis
  • Mesothelioma of the pleura
  • Sarcoidosis
  • Heart disease:
  • Any disease featuring chronic hypoxia
  • Cyanotic heart defect (most common cardiac cause)
  • Infective endocarditis
  • Atrial myxoma (benign tumor)
  • Arteriovenous fistula or malformation
  • Gastrointestinal and hepatobiliary:
  • Malabsorption
  • Crohn's disease and ulcerative colitis
  • Cirrhosis, especially in primary biliary cholangitis
  • Hepatopulmonary syndrome, a complication of cirrhosis
  • Others:
  • Graves' disease (autoimmune hyperthyroidism) – in this case, it is known as thyroid acropachy
  • Familial and hereditary clubbing and "pseudoclubbing" (people of African descent often have what appears to be clubbing)
  • Vascular anomalies of the affected arm such as an axillary artery aneurysm (in unilateral clubbing)
  • Primary hypertrophic osteoarthropathy

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. Another congenital form involves mutations in SLCO2A1, which cells use to uptake prostaglandin from the surroundings.

Pathogenesis

Most cases of nail clubbing appear linked to increased levels of platelet-derived growth factor (PDGF) and/or vascular endothelial growth factor (VEGF) signaling at the fingertips. Both have growth-promoting properties and cause vascular hyperplasia, capillary permeability (edema), and excessive fibroblast and osteoblast formation (hypertrophy of connective tissue including the bone). Specific causes include:

  • 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 entering the systemic circulation. In disorders where there is prominent extrapulmonary shunting of blood (e.g. cyanotic heart diseases, liver cirrhosis),
  • In cases or diffuse pulmonary diseases or lung cancer, the excess VEGF produced in the diseased parts of the lungs directly enter circulation.
  • Hypoxia induces the expression of VEGF by platelets.
  • No visible clubbing – Fluctuation (increased ballotability) and softening of the nail bed only. No visible changes in nails.
  • Mild clubbing – Loss of the normal <165° angle (Lovibond angle) between the nailbed and the fold (cuticula). Schamroth's window (see image) is obliterated. Clubbing is not obvious at a glance.
  • Moderate clubbing – Increased convexity of the nail fold. Clubbing is apparent at a glance.
  • Gross clubbing – Thickening of the whole distal (end part of the) finger (resembling a drumstick)
  • Hypertrophic osteoarthropathy – Shiny aspect and striation of the nail and skin

Schamroth's sign 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 the 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.

<gallery>

File:Clubbing of fingers.jpg|Severe clubbing

Clubbing2.JPG|Front view

Clubbing1.JPG|Side views

CongenitalHeartCase-133.jpg|Cyanotic nail beds

</gallery>

Epidemiology

thumb|Self-portrait by [[Dick Ket showing nail clubbing.]]

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, had significant underlying disease of various causes, while 60%, or nine patients, had no medical problems after further investigation and remained well over the subsequent year.

See also

  • Clubbed thumb (unrelated congenital deformity)

References