Clubbing

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.¹

Primary clubbing may be idiopathic or be a feature of an inherited condition. Secondary clubbing may be caused by a wide range of diseases.

Pachydermoperiostosis is a rare disease. 96 cases were reported in the literature between 1947 and 1990 and approximately 50 cases between 1990 and 2004.²

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.⁴ 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.⁵ Pseudo-clubbing may be seen in chronic renal failure,⁶ hyperparathyroidism,⁴ and sarcoidosis.⁷

Laboratory investigations

These will depend on the underlying conditions suggested by the overall clinical picture.

Imaging

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.¹ 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.