In medicine, clubbing (or digital clubbing) is a deformity of the fingers and fingernails that is associated with a number of diseases, mostly of the heart and lungs. Idiopathic clubbing can also occur. Hippocrates was probably the first to document clubbing as a sign of disease, and the phenomenon is therefore occasionally called Hippocratic fingers.

Signs and diagnosis

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Clubbing develops in five steps:Myers KA, Farquhar DR. The rational clinical examination: does this patient have clubbing? JAMA. 2001;286:341-7. PMID 11466101.

1. Fluctuation and softening of the nail bed (increased ballotability)
2. Loss of the normal <165° angle ("Lovibond angle") between the nailbed and the fold (cuticula)
3. Increased convexity of the nail fold
4. Thickening of the whole distal finger (resembling a drumstick)
5. Shiny aspect and striation of the nail and skin

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 may also be performed.

Disease associations

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Isolated clubbing

Clubbing is associated with:

• Lung disease:
  • Lung cancer, mainly large-cell (35% of all cases), not seen frequently in small cell lung cancerSridhar KS, Lobo CF, Altman RD. Digital clubbing and lung cancer. Chest 1998;114:1535-37. PMID 9872183
  • Interstitial lung disease
  • Tuberculosis
  • Bronchiectasis
  • Suppurative lung disease: lung abscess, empyema
  • Cystic fibrosis
  • Pulmonary hypertension
  • Mesothelioma
• Heart disease:
  • Any disease featuring chronic hypoxia
  • Congenital cyanotic heart disease (most common cardiac cause)
  • Subacute bacterial endocarditis
  • Atrial myxoma (benign tumor)
• Others:
  • Crohn's disease and ulcerative colitis
  • Hyperthyroidism (thyroid acropachy)
  • Liver diseases (in the "hepatopulmonary syndrome", a complication of cirrhosis)Naeije R. Hepatopulmonary syndrome and portopulmonary hypertension. Swiss Med Wkly. 2003;133:163-9. PMID 12715285.
  • Malabsorption
  • Vascular anomalies of the affected arm (in unilateral clubbing)

Although many of these associations are recognised (such as the link with lung cancer), some are based on a few observations and might be false. Prospective studies of patients presenting with clubbing have not been performed, and hence there are no reliable numbers as to the distribution of the causes and the prognosis.

HPOA

A special form of clubbing is hypertrophic pulmonary osteo-arthropathy, 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 associated almost exclusively with lung cancer. In dogs the condition is known as hypertrophic osteopathy.

Primary HOA

Primary hypertrophic osteo-arthropathy is HPOA without signs of pulmonary disease. This form has a hereditary component, although subtle cardiac abnormalties can occasionally be found. It is known in continental Europe as the Touraine-Solente-Golé syndrome.

Pathophysiology

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Even though clubbing is a well established physical finding in many diseases, the physiological mechanism that actually causes clubbing is not well established. Current understanding is that these diseases cause vasodilation in the distal circulation which leads to hypertrophy of the tissue of the nailbeds and thus to the clubbed fingernails.

Other factors that have been implicated are secretion of growth factors (such as hepatocyte growth factor) by pathologic lesions.

References

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Medical signs

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