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Finger clubbing: Causes, Grading and Schamroth’s sign

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  • Revised on: 2021-02-13

Finger clubbing is a deformity of the finger or toe nails due to a proliferation of connective tissue, on the dorsal surface of the fingers or toe nails.

clubbed finger

Clubbing is usually associated with lung diseases such as interstitial lung disease, lung infection, lung cancer or cardiovascular disorder with featured hypoxic state.

 

Sometimes there may be an associated increased sponginess of the soft tissue at the base of the clubbed nail.

This clubbing is painless soft tissue swelling of the terminal phalanges with an increase in the convexity of the nail.

Normally, when the distal phalanges of the corresponding fingers of the opposite hands are opposed, a small diamond shaped window is formed between the nail beds.

For finger clubbing to develop, it takes weeks or or even months and may disappear if the underlying condition is treated.

Clubbing usually occurs symmetrically meaning it involves fingers or toes of both hands This clubbing may occur on one hand or toes (unilateral clubbing) in cases of proximal vascular conditions such as arteriovenous shunts that are used for dialysis.

Clubbing is thought to occur as a result of humoral substances which cause dilation of the vessels  and increased blood flow through multiple arteriovenous shunts in the distal phalanges as well as growth factors released from platelet precursors in the digital circulation.

What are the causes of finger clubbing

The causes of clubbing may be classified as either congenital, idiopathic or acquired

Acquired causes include;

  • Lung cancer
  • Bronchiectasis
  • Cystic fibrosis
  • Chronic suppurative conditions
  • Pulmonary fibrosis
  • Lung abscess
  • Empyema
  • Mesothelioma
  • Fibroma

Cardiovascular causes associated with hypoxia such as

  • Congenital heart disease
  • Arteriovenous shunts
  • Aneurysms
  • Infective endocarditis

Other causes include;

Thyrotoxicosis- In autoimmune hyperthyroidism with thyroid acropachy – clubbing usually occurs on the radial side of the hand.

Finger clubbing is reversible following lung transplantation for cystic fibrosis.

Examination for clubbing

When examining finger clubbing on a patient you are required to look across the nail bed from the side of each finger and observe the distal phalanges nail bed and the nail.

Then move on to measure the anteroposterior distance at the level of the interphalangeal joint and at the level of the nail bed.

The third step is to measure the nail bed angle known as Lovibond angle.

The fist step is to place the nails of corresponding fingers of the opposite hand back to back and look for a visible gap between the nail beds known as the Schamroth’s window sign or Schamroth’s test.

The sixth step is to place your thumbs under the pulp of the distal phalanx and use your index fingers alternately to see if you can feel movement of the nail on the nail bed. This is fluctuation.

Findings

From the examination, finger clubbing is present if:

  1. There is absent Schamroth’s window sign and,
  2. The interphalangeal depth ratio (B/A is greater than 1
  3. The nail bed angle is  more than 190°

Schamroth’s sign or schamroth’s window test.

Schamrochs test is a test for finger clubbing that was brought up by acardiologist known as Leo Schamroth.

When the dorsum of the distal phalanges of the fingers of both hands are approximated to each other, a diamond shaped gap is made out due to the presence of the normal Lovibond angle.

This gap dissapears with obliteration of this angle as occurs with finger clubbing

A positive Schamroth sign occurs when this Lovibond angle is obliterated and finger clubbing is present whereas a  negative or normal Schamroth sign is when the diamond-shaped space formed by the dorsal surface of the nails is present.

Schamroth’s sign

Stages of finger clubbing

Finger clubbing can be graded into four main grades,Grade 1-IV

Grade I(Mild clubbing)

In this grade there is an obliteration of the Lovibond angle (<165 degrees) of the nail bed an positive fluctuation test.

The schamroth’s window is obliterated but the clubbing isnt obvious at a glance.

Grade II(Moderate clubbing)

Finger clubbing grade II has a parrot beak appearance with an increased convexity of the nail fold and its usually apparent from a glance.

Grade III (Gross clubbing)

In this grade there is a thickening of the whole distal finger which then has a drumstick appearance.

Grade IV(Hypertrophic osteoartropathy)

This grade is also referred to as Hypertrophic osteoartropathy which appears like a shiny aspect and striation of the nail and skin.

Hypertrophic osteoarthropathy occurs in patients who have primary and metastatic lung cancer,mesothelioma, bronchiectasis, or liver cirrhosis.

Here, the subperiosteal formation of new bone in the distal diaphyses of the long bones  of the extremities causes pain and symmetric arthritis-like changes in the shoulders, knees, ankles, wrists, and elbow joints.