Clubbing of Fingers: Causes, Mechanism, Grades & Schamroth's Sign

Definition: Bulbous enlargement of soft parts of the terminal phalanges with both transverse and longitudinal curving of the nails. It occurs due to interstitial edema and dilation of arterioles & capillaries.

Mechanism

1. The exact mechanism is not known. It is believed that the stimulus for clubbing is hypoxia.
   • Hypoxia leads to opening of deep arteriovenous fistulas.
   • This increases the blood supply of the fingers and toes causing it to hypertrophy.
2. Ferritin Hypothesis:
   • When reduced ferritin in venous blood escapes oxidation in the lungs and enters the systemic circulation...
   • It causes dilation of arteriovenous anastomosis and hypertrophy of the terminal phalanx resulting in clubbing.
3. Platelet-derived growth factor causing vasodilatation.

Causes

1. Pulmonary

• Bronchogenic carcinoma, Mesothelioma
• Lung Abscess, Empyema, Bronchiectasis
• TB with secondary infection
• Diffuse fibrosing alveolitis

2. Cardiac

• Infective Endocarditis
• Cyanotic Congenital Heart Diseases, Eisenmenger's physiology
• Atrial Myxoma

3. Alimentary

• Ulcerative Colitis, Crohn's disease
• Cholangiolitic & Biliary cirrhosis
• Hepatopulmonary syndrome

4. Endocrine

• Myxedema
• Thyroid Acropachy (Grave's disease)
• Acromegaly

5. Miscellaneous

• Hereditary / Idiopathic
• Unilateral: Pancoast tumor, Subclavian/Innominate artery aneurysm
• Uni-digital: Trauma or Tophi deposit in gout
• Upper limb only: Heroin addicts (chronic obstructive phlebitis)

Grades

Grade	Description
I	Softening of nail bed (Fluctuation test positive).
II	Obliteration of the angle of the nail bed (Lovibond angle).
III	"Parrot beak" or "Drumstick" appearance. Skin becomes shiny/tense.
IV	HPOA: Hypertrophic Pulmonary Osteoarthropathy. Swelling of fingers + Pain/Swelling of wrist/hand + Periosteal new bone formation.

Schamroth's Sign

Normally when two fingers are held together with nails facing each other, a diamond-shaped space is seen at the level of proximal nail fold. This is lost in clubbing.