Clubbing is defined as selective bulbous enlargement of the distal segment of a digit due to an increase in soft tissue.
Mechanisms responsible for clubbing:
1. Humoral theory states that an unidentified humoral substance causes dilatation of the blood vessels of the finger tip.
2. Persistent hypoxia causes opening up of the deep arteriovenous fistulae of fingers .
3. Reduced ferritin in systemic circulation causes dilatation of the arteriovenous anastomosis and hypertrophy of the terminal phalanx.
4. Vagal theory states that persistent vagal stimulation causes vasodilation and clubbing.
5. Circulating megakaryocytes and large platelet particles which are normally destroyed by the lung reach the distal extremities and interact with endothelial cells. This leads to liberation of platelet derived growth factor (PDGF) which leads to proliferation of connective tissue. This causes clubbing and hypertrophic osteoarthropathy.
6. Unilateral clubbing is seen in neurological disorders like hemiplegia, in vascular disorders like arteriovenous malformations, dialysis fistula.
7. Unidigital clubbing is seen in repeated trauma.
Causes of clubbing include the following: (mnemonic- CLUBBING)
C- Cardiac- Cyanotic congenital heart diseases, Infective endocarditis
L- Lung- Lung abscess, Interstitial lung disease, Pulmonary AV fistula, Empyema
U– Ulcerative colitis
B- Bronchogenic carcinoma
I- Idiopathic, Hereditary
N – –
G- Gastric- Crohn’s disease, Hepatoma, Liver cirrhosis
Grades of clubbing
I– Increased fluctuation of nail bed
II– Obliteration of the angle between the nail and nail bed
III– Increased curvature of the nail resulting in a parrot beak or drumstick appearance
IV– Hypertrophic osteoarthropathy (characterised by digital clubbing, arthritis, periostitis resulting in painful, tender, swelling of wrists, ankles, elbows and knees)