Digital clubbing or nail clubbing or finger clubbing is bulbous enlargement of soft parts of the terminal phalanges with both transverse and longitudinal curving of the nails. The swelling of the terminal phalanges in clubbing occurs due to interstitial edema and dilation of the arterioles and capillaries.
Digital clubbing is also called finger nail clubbing or nail clubbing. Drumstick fingers and watch-glass nails are other names for these deformed nails.
Though clubbed fingers are mostly asymptomatic, these may predict the presence of some dreaded underlying diseases. Clubbing of nails results in increase in both anteroposterior and lateral diameter of the nails. Clubbing was first described by Hippocrates nearly 2500 years ago in a patient with empyema. and is regarded to be the oldest sign in clinical medicine.
Digital clubbing may occur as isolated finding or is often part of the syndrome of hypertrophic osteoarthropathy.
Grades of Clubbing
- Fluctuation and softening of the nail bed (increased ballotability)
- Loss of the normal <165° angle (Lovibond angle) between the nailbed and the fold (cuticula)
- Increased convexity of the nail fold
- Thickening of the whole distal (end part of the) finger (resembling a drumstick)
- Shiny or glossy changes in nail with striation of the nail and skin
The process usually takes years but in certain conditions like lung abscess, empyema of thorax, clubbing may develop quite fast.
Grading of clubbing has no clinical significance.
Causes of Digital Clubbing
Many conditions from different organ systems may produce digital clubbing. The are
- Bronchogenic carcinoma
- Lung abscess
- Tuberculois with secondary infection
- Diffuse fibrosing alveolitis
- Infective endocarditis
- Cyanotic heart disease
- Congenital heart disease
- Ulcerative colitis
- Crohn’s disease
- Cholangiolitic cirrhosis
- Inflmmatory Bowel Disease
- Iatrogenic myxedema
- Unilateral- Pancoast tumor, subclavian and innominate artery aneurysm
- Unidigital- Traumatic or gout deposit
- In heroin addicts due to chronic obstructive phlebitis [inflammation of vein]
Mechanism of Clubbing
The exact mechanism is not known. It is believed that the stimulus for clubbing is hypoxia. Hypoxia leads to opening up of deep arteriovenous fistulas which increase the blood supply of the fingers and toes causing it to hypertrophy.
Another hypothesis is that when reduced ferritin in venous blood escapes oxidation in the lungs and enters the systemic circulation., it causes dilation of arterio-venous anastomosis and hypertrophy of the terminal phalanx resulting in clubbing.
Most acceptable hypothesis so far suggests that megakaryocyte or platelet clusters, lodged in the peripheral vessels of the digits, release platelet-derived growth factor or vascular endothelial growth factor to cause dilatation of vessels and lead to the increased vascularity, permeability, and connective tissue changes that are the hallmark of clubbing.
Assessment of Clubbing
Clubbing can be assessed by physical examination. However, it is subjective and often unreliable, particularly in mild. Computerized analysis have been used to objectively assess clubbing.
Different signs of clubbing are
It was proposed by Lovibond and is also called Profile angle. It is defined by the angle made by nail as it exists from the proximal nail fold. In normal subjects, profile angle is usually less than 165 degrees. Profile angle of greater than 180° can be used to differentiate true clubbing from simple nail curving and paronychia.
It is constructed by drawing a line from distal digital crease to the cuticle and another line from the cuticle to hyponychium [see above]. Normal hyponychial angle is less than 192°. Hyponychial angle is a preferred objective criterion for clubbing because it is independent of age, sex, height, and weight of the patient and correlates with the subjective assessment of clubbing.
Phalangeal Depth Ratio
It is the ratio of digit’s depth measured at the junction between skin and nail (nail bed) and at the distal interphalangeal joint. Normally, the depth at distal interphalangeal joint is more than the depth at nail bed but in clubbed fingernails, connective tissue deposition expands the pulp in the terminal phalanx and the ratio becomes reversed. This ratio is also independent of age, sex, and ethnicity of population.
A Phalangeal depth ratio of over 1 is indicative of clubbing.
It is the sum of phalangeal depth ratio for all 10 fingers. A digital index of 10.2 or higher is indicative of clubbing. Digital index is more specific for clubbing than phalangeal depth ratio.
Schamroth’s Test or Schamroth’s Window Test
This test was originally demonstrated by South African cardiologist Dr Leo Schamroth on himself and is a popular test for clubbing.
When the distal phalanges (bones nearest the fingertips) of corresponding fingers of opposite hands are directly apposed (placed against each other back to back), a small diamond-shaped “window” is normally apparent between the nailbeds.
If this window is obliterated, the test is positive and clubbing is present. Though popular, this test is not very accurate.
Precision and accuracy of this sign is not known.
Clubbing in Different Conditions
There are several reports of tuberculosis associated with clubbing.
Interstitial Lung Disease
Idiopathic pulmonary fibrosis is the most common pulmonary cause of digital clubbing. Asbestosis is also commonly associated but sarcoidosis is rarely associated.
Lung malignancy is a predominant cause of clubbing, contributing to nearly 90% of pulmonary associations of clubbing.
However, only 5-15% of lung cancer patients have clubbing.
Clubbing is also the most common paraneoplastic syndrome in lung cancer patients and most common association is of non small cell type.
Malignant mesothelioma, pleural fibroma, and metastatic osteogenic sarcoma may also cause clubbing.
Hypertrophic pulmonary osteoarthropathy or Pierre Marie-Bamberger syndrome is combination of clubbing and thickening of periosteum and synovium. It is commonly associated with lung cancer.
Primary hypertrophic ostoarthropathy is also found and occurs without signs of pulmonary disease and has hereditary component.
Digital clubbing is reported to be commonly associated with inflammatory bowel disease and is more significantly associated with active disease than inactive. Behcets disease]and hepato-pulmonary syndrome are rare causes of clubbing. Digital clubbing is mainly reported in biliary cirrhosis but has also been described in other liver diseases, such as portal cirrhosis, secondary hepatic amyloidosis, alcoholic cirrhosis, and biliary atresia.
Clubbing in Endocrine Disease
Thyroid acropachy is an extra-thyroidal manifestation of autoimmune thyroid disease and is frequently associated with dermopathy and ophthalmopathy. It is characterized by clubbing and swelling of the fingers and toes, with or without periosteal reaction of the distal bones. It can also occur with euthyroid and hypothyroid state.
Clubbing has been reported in hyperparathyroidism.
Human Immunodeficiency Virus And Clubbing
Few cases have reported linking of HIV infection and but is controversial
Infective endocarditis usually causes a milder form of clubbing, whereas in congenital cyanotic heart disease, gross, drumstick appearance may be seen.
Clubbing is generally bilateral, but in some conditions it may occur unilaterally. Unilateral clubbing is usually associated with local vascular lesions of the arm, axilla, and thoracic outlet and with hemiplegia.
Aneurysm of the subclavian artery, is commonly reported in the literature to cause unilateral clubbing. Aortic aneurysm and innominate artery aneurysm have also been reported.
Unilateral clubbing also occurs in arm affected by hemiplegia. The pathogenesis of clubbing in hemiplegia is not clear.
Clubbing may also involve single digit only in case of digital mucoid cyst, osteoid osteoma, myxochondroma, and enchondromas.
Occasionally, clubbing may occur in lower limbs, sparing the upper limbs. This is known as differential clubbing. Differential clubbing may occur in patient with patent ductus arteriosus associated with pulmonary artery hypertension and right to left shunt.
Congenital nail clubbing is known to occur and is usually symmetrical and bilateral, but different fingers and toes may be involved to varying degrees. Some fingers or toes may be spared, but the thumbs are almost always involved.
In hyperparathyroidism excessive bone resorption may result in disappearance of the terminal phalanges with telescoping of soft tissues and a drumstick appearance of the finger resembling clubbing. However, the curvature of the nail is not present.
Images Credit: Sarkar M, Mahesh DM, Madabhavi I. Digital clubbing. Lung India : Official Organ of Indian Chest Society 2012;29(4):354-362. doi:10.4103/0970-2113.102824.