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

Clubbing of the fingernail. The red line shows the outline in clubbing

Clubbing develops in five steps (Myers et al):

1. Fluctuation and softening of the nailbed
2. Loss of the normal <165° 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 encountering clubbing in a patient, a doctor will conduct a detailed medical interview (e.g. smoking history) and a physical examination to find positive clues of associated disease. Generally, an X-ray of the chest is also made.

Disease associations

Isolated clubbing

Clubbing is associated with:

• Lung disease:
  • Lung cancer, mainly large-cell (35% of all cases, see Sridhar et al)
  • Interstitial lung disease
  • Tuberculosis
  • Bronchiectasis
  • Suppurative lung disease: lung abscess , empyema
  • Cystic fibrosis
  • Pulmonary hypertension
  • Mesothelioma
  • Emphysema (rarely)
• Heart disease:
  • Any disease featuring chronic hypoxia
  • 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, see Naije)
  • 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.

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

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

• Sridhar KS, Lobo CF, Altman RD. Digital clubbing and lung cancer. Chest 1998;114:1535-37. PMID 9872183.
• Myers KA, Farquhar DR. The rational clinical examination: does this patient have clubbing? JAMA 2001;286:341-7. PMID 11466101.
• Naeije R. Hepatopulmonary syndrome and portopulmonary hypertension. Swiss Med Wkly 2003;133:163-9. PMID 12715285.