Digital clubbing is one of the oldest recognised signs in medicine, first formally documented by Hippocrates nearly 2500 years ago. For this reason, it is also known as “Hippocratic fingers”.
It is an important clinical sign that can assist in the diagnosis of a variety of conditions, particularly when found in conjunction with other symptoms and signs. Digital clubbing is characterised by a painless and bilateral increase in the soft tissue around the end of the fingers and toes.
Pathogenesis
The exact pathogenesis of digital clubbing is not fully understood, but it is thought to result from changes to the volume of interstitial fluid and increased blood flow to the area. Platelet-derived growth factor and vascular endothelial growth factor are believed to be involved in this process.
Aetiology
Digital clubbing is associated with a wide variety of clinical condition. The commonest causes lung diseases, with neoplastic lung disease being the most common respiratory cause of clubbing.
The following table summarises the most common causes:
| System involved | Examples |
|---|---|
| Primary clubbing | Primary hypertrophic osteoarthropathy (pachydermoperiostosis) Genetic (familial clubbing) Hypertrophic osteoarthropathy |
| Cardiac disease | Cyanotic congenital heart disease Bacterial endocarditis |
| Respiratory disease | Lung cancer Tuberculosis Bronchiectasis Cystic fibrosis Interstitial lung disease Cryptogenic fibrosing alveolitis Idiopathic pulmonary fibrosis Sarcoidosis Empyema Pleural mesothelioma Pulmonary metastases |
| Gastrointestinal disease | Ulcerative colitis Crohn's disease Primary biliary cirrhosis Cirrhosis of the liver Oesophageal achalasia Peptic ulceration |
| Endocrine disease | Acromegaly Thyroid acropachy |
| Dermatological disease | Bureau-Barrière-Thomas syndrome Fischer's syndrome Palmoplantar keratoderma |
| Malignancy | Thyroid cancer Thymus cancer Hodgkin disease Disseminated chronic myeloid leukaemia |
Clinical presentation
There is typically bilateral swelling of the distal portion of the fingers or toes. The onset is slow and may go unnoticed by the patient. Digital clubbing is generally painless, but some patients report mild discomfort. It is most commonly discovered as part of an examination for other presenting symptoms.
Prominent digital clubbing Wikipedia
Courtesy of Desherinka CC BY-SA 4.0
As clubbing progresses, The Lovibond angle (the angle between the nail and the nail base) becomes obliterated. The Lovibond angle is less than or equal to 160° in normal circumstances. With increasing convexity of the nail, the angle becomes greater than 180°. In the early stages of clubbing, the nail may feel springy instead of firm when palpated, and the skin at the base of the nail may become smooth and shiny.
In individuals without clubbing, if two opposing fingers are placed together, a diamond-shaped window will appear. In the presence of digital clubbing, this window is obliterated, and the distal angle formed by the two nails becomes wider. This is known as Schamroth’s window test.
A normal Samoroth’s window test in a patient without digital clubbing
Grading
Digital clubbing is graded as follows:
| Grade | Description |
|---|---|
| Grade 1 | Fluctuation or softening of the nail bed |
| Grade 2 | Increase in the Lovibond angle to greater than 160° |
| Grade 3 | Accentuated convexity of the nail |
| Grade 4 | Clubbed appearance of the fingertip |
| Grade 5 | Development of a shiny or glossy change in the nail and adjacent skin with longitudinal striations |
Thank you to the joint editorial team of www.plabprep.co.uk for this ‘Exam Tips’ post.
