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Synonyms: Hippocratic nails, Hippocratic fingers (first described by Hippocrates)
This describes an increase in the soft tissue around the end of the fingers and toes. The swelling is painless and usually bilateral, unless a localised vascular abnormality exists. There is no change to the underlying bone. The nail base eventually becomes convex and extends halfway up the nail.
Clubbing is thought to result from changes to the volume of interstitial fluid and increased blood flow to the area but the exact pathophysiology remains unknown.
Primary clubbing may be idiopathic or be a feature of an inherited condition. Secondary clubbing may be caused by a wide range of diseases.
|Causes of Clubbing|
|Primary ||Pulmonary disease||Cardiac disease|
|Gastrointestinal disease||Skin disease ||Malignancies |
Pachydermoperiostosis is rare and is characterised by skin thickening of the forehead, eyelids and hands, digital clubbing and periostosis.The epidemiology of secondary clubbing depends on the cause.
The patient may notice a swelling of the distal portion of the fingers or toes but the onset is usually so gradual as to make this a rare occurrence. Even more rarely, the patient may notice some discomfort, because most clubbing is painless. The majority of clubbing is detected by doctors as part of a routine examination for other presenting symptoms.
Clubbing has been described as a bulbous fusiform enlargement of the distal portion of a digit. It is commonly bilateral but may be unilateral and can affect a single digit. Both fingers and toes can be affected.
As clubbing progresses, the angle between the nail and the nail base (called the Lovibond angle) becomes obliterated. Normally, the angle is less than or equal to 160°. With increasing convexity of the nail, the angle becomes greater than 180°. In early 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 clubbing, this window is obliterated and the distal angle formed by the two nails becomes wider. This is known as Schamroth's window test.
Pseudo-clubbing - this is overcurvature of the nails in both the longitudinal and transverse axes, with preservation of a normal Lovibond angle. The main features of pseudo-clubbing seen in one study were asymmetrical finger involvement and acro-osteolysis. Whilst these were present in the majority of cases they were also present in some cases of clubbing, so could not be said to be pathognomonic. Pseudo-clubbing may be seen in chronic kidney disease, hyperparathyroidism, sarcoidosis, scleroderma, subungual haematoma and chromosome deletion.
These will depend on the underlying conditions suggested by the overall clinical picture.
This is not usually required to diagnose clubbing but plain radiographs of the digits may help to elucidate the cause. Osteolysis is often seen in patients with congenital cyanotic heart disease, whilst bone hypertrophy suggests a pulmonary condition.
Other modalities sometimes employed in clinical and research settings include technetium-99m scanning to assess bone loss, thermography and positron emission tomography (PET) scanning.
CT and MRI scanning of other areas may be required to assist in diagnosing the underlying primary cause.
This will be dictated by the underlying disease process.
Clubbing is potentially reversible if the underlying condition is treated early enough but the changes may be irreversible once collagen deposition has set in.
Further reading and references
; DermNet NZ
; Mutations in the prostaglandin transporter encoding gene SLCO2A1 cause primary hypertrophic osteoarthropathy and isolated digital clubbing. Hum Mutat. 2012 Apr33(4):660-4. doi: 10.1002/humu.22042. Epub 2012 Feb 24.
; Evaluation of a simple bedside tool developed to measure different parameters of clubbing. Lung India. 2011 Jul28(3):228-9.
; Clubbing: an update on diagnosis, differential diagnosis, pathophysiology, and clinical relevance. J Am Acad Dermatol. 2005 Jun52(6):1020-8.
; Pachydermoperiostosis in an African patient caused by a Chinese/Japanese SLCO2A1 mutation-case report and review of literature. Semin Arthritis Rheum. 2014 Feb43(4):566-9. doi: 10.1016/j.semarthrit.2013.07.015. Epub 2013 Sep 5.
; Images in clinical medicine. Pseudoclubbing. N Engl J Med. 2006 Apr 13354(15):e14.
; Pseudoclubbing: Is It Different from Clubbing? Semin Arthritis Rheum. 2008 Mar 29.
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