Nail clubbing is not specific to chronic obstructive pulmonary disease. Therefore, in patients with COPD and significant degrees of clubbing, a search for signs of bronchogenic carcinoma might still be indicated. A congenital form has also been recognized.
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 coding for the enzyme 15-hydroxyprostaglandin dehydrogenase ; this leads to decreased breakdown of prostaglandin E2 and elevated levels of this substance.
Pathophysiology
The exact cause for sporadic clubbing is unknown. Theories as to its cause include:
Vasodilation.
Secretion of growth factors from the lungs.
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 and vascular endothelial growth factor. PDGF and VEGF have growth promoting properties and cause connective tissue hypertrophy and capillary permeability.
Diagnosis
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.
Stages
Clubbing is present in one of five stages:
No visible clubbing - Fluctuation and softening of the nail bed only. No visible changes of nails.
Mild clubbing - Loss of the normal <165° angle between the nailbed and the fold. Schamroth's window 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 finger
Hypertrophic osteoarthropathy - Shiny aspect and of the nail and skin
Schamroth's test or Schamroth's window test is a popular test for clubbing. When the distal phalanges of corresponding fingers of opposite hands are directly , a small diamond-shaped "window" is normally apparent between the nailbeds. If this window is obliterated, the test is positive and clubbing is present.
Epidemiology
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.
History
At least since the time of Hippocrates, clubbing has been recognized as a sign of disease. The phenomenon has been called "Hippocratic fingers".
