A Detailed Analysis of Finger Clubbing

Many times, we come across the word ‘clubbing’ and wonder whether it is a medical term or implies the usual understanding of clubbing we all generally have. Finger clubbing is a serious medical condition, which has become increasingly common in clinical settings, these days. It is important to understand that finger clubbing is symptom and not a disease. The presence of finger clubbing can be a helpful indication of a serious underlying pathology.

Finger clubbing is a serious medical condition or disorder, which is characterized by changes within and under the fingernails and toenails. The nails and nails beds undergo enlargement, which presents as a bullous swelling and may depict changes in the texture and color of the nails and nail beds. The contour of the nails is severely disturbed as well. Changes in the appearance also occur in areas around the nails i.e. in fingers and toes.

Finger clubbing, which is sometimes also referred to as digital clubbing (since nails of the digits i.e. finger and toes are affected), is a disfigurement or abnormality of the nails and fingers, which is never seen in physiological circumstances and always indicates an underlying pathology. The entire shape and presentation of the nails along with neighboring structures is severely distorted giving a gruesome appearance. It is usually a symmetrical finding on clinical examination and most often affects fingernails. Unilateral fingernail clubbing is seen in some rare conditions only.

Finger clubbing is seen as a symptom in several disorders, but most often it is seen in an individual suffering from a heart or lung disorder. Therefore, almost all smokers are positive for clubbing due to extensive lung damage. Disorders in other organs such as liver, gastrointestinal tract and in cases of certain autoimmune disorders of the body, finger clubbing is a common symptom that can be seen in the patient.

Finger clubbing can sometimes be idiopathic, i.e. no reason or cause can be identified. This is a very rare condition and is seen in about 1% (according to recent statistics; Harvard, 2011) of the patients. Being discovered by Hippocrates, the term Hippocratic fingers is also used sometimes to describe clubbing.

There are several grades and stages of clubbing which can be only be understood after understanding the pathology of the changes.

Finger clubbing is best described as a painless swelling or enlargement of the terminal phalanx of the fingers. This enlargement distorts the normal architecture of the nails, giving rise to a number of changes. The underlying mechanism of clubbing can be simply described by stating that clubbing is a direct result of the soft tissue proliferation of the nail bed. There are 4 theories which shall help in understanding the mechanism of this proliferation and the development of clubbing which are as follows:-

1. Platelet derived growth factor theory: Whenever the body undergoes stress due to inflammation, inflammatory products are released in the blood, which causes multiple changes as a protective measure against the stress. In cases of chronic inflammation usually seen in diseases like tuberculosis, bronchiectasis, chronic pneumonia and so forth, there is an influx of acute phase reactants or acute phase proteins, which mediate damage and changes. Acute phase proteins are always released in response to inflammation in the body by the cytokines, especially Interleukin 1, Interleukin 6, interleukin 8 and Tumor Necrosis Factor- alpha.

   A few common acute phase proteins mediating damage in chronic inflammation include C-reactive protein, ferritin, ceruloplasmin, complement factors, mannose-binding protein and so forth. Acute phase proteins travel to the capillaries in the nail beds and stimulate production of platelets and megakaryocytes, which cause vascular connective tissue proliferation. Once the connective tissue proliferates, it increases the underlying matrix and stimulates the proliferation of the soft tissue in the nail beds and hence results into finger clubbing. The entire procedure of proliferation is mediated by megakaryocytes and platelet derived growth factor, imparting the name to the theory as well.

2. Chronic Hypoxia Theory: If any patient suffers from chronic hypoxia or diseases, which cause chronic hypoxia; have been seen to contribute to finger clubbing. Diseases such as COPD (chronic bronchitis, emphysema, asthma, and bronchiectasis), heart failure and so forth decrease the oxygen saturation of blood and decrease the amount of oxygen being delivered to tissues. Conditions like anemia, especially iron-deficiency anemia decreases the oxygen carrying capacity of blood and decrease the oxygen supply to tissues causing tissue hypoxia. As tissues undergo hypoxia, they initiate systemic vaso-dilation, which refers to a dilation of the vessel lumen due to loss of vessel tone (the smooth muscles relax tonically) and increase blood flow. As vasodilation occurs, blood flow to tissues increases in hopes of increasing the oxygen concentration or supply by blood. Increased blood flow, especially to the periphery delivers more blood to the digits and as a result, enhanced blood flows to the extremities. As blood flow increases, it exposes the soft tissue in the nail beds to growth factors, which stimulate growth and proliferation of the tissues. As blood flow remains high, growth factors keep pooling and cause soft tissue proliferation, which subsequently causes clubbing of the finger nails. Increased blood flow also brings along with it more vasodilators such as bradykinin, prostaglandins, PTH, and estrogen. Estrogen is a potent vasodilator which may be primary causative factor of clubbing in females. In addition, tissue hypoxia, or chronic hypoxic conditions in the tissues cause opening of the AV (arteriovenous) fistulae in the terminal phalanx. This increases local vasodilation and directly stimulates the proliferation of soft tissue in the nail beds due to uninterrupted increased blood flow.

3. Hormonal Theory: Increased hormones in the blood or plasma can directly cause proliferation of soft tissue and smooth muscles. Hormones which promote growth and development, such as the growth hormone, thyroid hormone and cortisol play an important role in the proliferation of the soft tissues in the nail beds. In conditions like acromegaly or pituitary adenoma, growth hormone is released in excess which works similar to insulin-like growth factor. It stimulates protein synthesis in cell and promotes gluconeogenesis and glycolysis making energy available for growth and protein synthesis due to an uninterrupted supply or exposure to growth hormone. In such conditions growth of new tissue becomes very favorable and soft tissue proliferation occurs in the nail beds giving rise to finger clubbing. Conditions like Addison’s disease, Grave’s disease, hyperthyroidism, acromegaly etc., have similar effects on the soft tissue of the nail beds and contribute to finger clubbing in a similar fashion.

4. Neurogenic Theory: In debilitating diseases of the brain or degenerative disorders, vagal stimulation can sometimes get out of hand. Increased vagal stimulation of the nerve endings due to a prolonged stimulus or irritation of the neurons can be a cause of vasodilatation. Prolonged vasodilation causes increased blood flow and a vicious cycle is initiated with an influx of more vasodilators and growth factors which promote growth and cause soft tissue proliferation of the nail beds eventually resulting in finger clubbing.

There are approximately 5 grades of finger clubbing that have been identified in clinical settings which are as follows:-

Grade-1 Finger Clubbing: This grade of finger clubbing is characterized by a ‘positive fluctuation test’ of the nails. Due to increased metabolism of the soft tissue in the nail beds and soft tissue proliferation, there is an increased volume of blood in the nail bed which leads to fluid accumulation within the nail and produces fluctuation of the nails, giving result to a positive fluctuation test. Nails are usually firm, but develop fluctuation due to clubbing, which is a way to arrive at positive fluctuation test.

Grade-2 Finger Clubbing: The second grade of finger clubbing is referred to as the obliteration of the Lovibond angle. The Lovibond angle is the angle that is formed between the nail and the skin. It is usually less than or equal to 160 degrees. Due to soft tissue proliferation, the antero-posterior diameter of the pulp increases which causes the Lovibond’s angle to be greater than 160 degrees.

Grade-3 Finger Clubbing: The third grade of Finger Clubbing is characterized by a parrot beak appearance of the finger nail when viewed from the lateral view.

Grade-4 Finger Clubbing: When the distal or terminal phalanx swells up more than the nail or the proximal phalanx, it gives a drumstick appearance. The distal portion of the finger increases in width and diameter and gives a drumstick appearance.

Grade-5 Finger Clubbing: This grade of finger clubbing is referred to as hypertrophic osteoarthropathy. This is a condition in which the nails along with the joints are affected collectively and cause clubbing. In some areas of the world, such as in Europe, hypertrophic osteoarthropathy is also known as Pierre Marie Bamberger syndrome. This condition is characterized by clubbing in association with swelling and sclerosis of the periosteum and synovium of the distal phalangeal joints and the interphalangeal joints. It is often misdiagnosed as arthritis. New bone starts developing and depositing in response to the continuing inflammation, which results in formation of thick sclerotic and weak bones. In hypertrophic osteoarthropathy, the skin of the finger and around the nail bed appears tight and shiny or glossy.

Stage-1 of Finger Clubbing: It is characterized by the normal appearance and angle of the nail, but increase in the flatulence of the nail bed.

Stage-2 of Finger Clubbing: This stage of finger clubbing is characterized by the initiation of the loss of angle between the nail and nail bed.

Stage-3 of Finger Clubbing: During this stage of finger clubbing, an increase in the curvature of the nails or loss of convexity is noticed, which is termed as koilonychias. The nails become thin as well as concave in shape.

Stage-4 of Finger Clubbing: In stage four of finger clubbing, the expansion of distal phalanx occur which gives the nails a drumstick appearance.

Stage-5 of Finger Clubbing: The presence of schamroth’s window is an indication of the stage 5 of finger clubbing. A small diamond like gap can be noticed between the nail and the nail bed in this stage, which is a definite way to diagnose finger clubbing.

There are 5 main characteristics of finger clubbing which are as follows: –

Koilonychia: Koilonychia refers to an increase in the nail curvature. This occurs when nails lose their convexity and become concave or spoon shaped nails. Transverse furrows develop between the nail and the nail bed, which contribute in the separation of the nail from the nail bed. Koilonychia is a painless characteristic of clubbing which persists during the disease as well as after the treatment of the disease.

Soft Tissue Hypertrophy: This finger clubbing feature refers to the soft portion in the terminal phalanx i.e. the pulp region which undergoes hypertrophy under various stimuli. This results in an edematous, elastic periungual swelling of the pulp.

Hyperplasia of the Fibro-Vascular Core: This feature of finger clubbing is one of the earliest signs of clubbing that reflect hyperplasia of the fibro-vascular core in the dermis, which then extends up to the matrix of the nail and nail bed. As a result of this, the mobility of the nails increases and the nail can be moved over the nail bed giving a sensation of the nail floating on an edematous bed.

Cyanosis: In this characteristic feature of finger clubbing, the nail beds appear bluish purple in color due to vasoconstriction of the capillaries in the nail beds as a result of compression from hypertrophy and hyperplasia of the overlying structures.

Leukonychia: This feature of finger clubbing refers to the whitish discoloration of the nails or milk spots appearing on the nails. During the later stages of the disease, clubbing nails lose their color and become completely white.

Clubbing develops quickly; however, this disorder can be resolved, once the underlying cause is identified and treated. Some of the causes of finger clubbing are:

Diseases of almost all of the major organs of the human body show signs of finger clubbing. By far the most common cause of finger clubbing is lung cancer. Any pathology of the lung that decreases the amount of oxygen in the circulating blood results in finger clubbing. This includes bronchiectasis, lung abscess, cystic fibrosis, interstitial lung diseases, empyema, pleural mesothelioma etc.

• Congenital anomalies of the heart (tetralogy of Fallot) and infectious endocarditis are also some major causes of finger clubbing.
• The gastrointestinal tract and liver disorders that cause finger clubbing include celiac disease, malabsorption, dysentery, Crohn’s disease, biliary and liver cirrhosis, hepatopulmonary syndrome.
• Some other conditions that show signs of finger clubbing are grave’s disease, axillary artery aneurysm, familial clubbing, Hodgkin lymphoma and overactive thyroid gland.

As mentioned above, finger clubbing is not a disease, but it is a symptom which is why it needs to be seen and confirmed during a clinical examination. Once finger clubbing is confirmed upon a clinical examination, relevant tests are to know the probable causes of finger clubbing. Finger clubbing can be diagnosed by the following:

• The nail is checked over the nail bed to see if it is mobile or any degree of fluctuation is present or not. This helps in determining the relevant stage or grade of finger clubbing present in the patient.
• The angle of the nail or the lovibond’s angle is determined by placing a card horizontally on the nail and is checked to see the presence of or obliteration of the angle
• Schamroth’s window is examined by placing the thumbs of both hands together in an inverted position and looking for a small space or window between the two nails. If the space is present then schamroth’s window is confirmed and is considered as a definitive sign of finger clubbing.
• Cyanosis or discoloration of the nail beds can be examined by the clinician during a general physical exam by looking at the nails in bright light against a white background.

In order to treat finger clubbing, the underlying cause of the clubbing needs to be treated. The physician should first gather a definitive diagnosis of the condition causing finger clubbing and then proceed with the treatment plan for the patient. Treatment options include chemotherapy, radiotherapy, surgery, NSAIDs, analgesics and so forth.

As soon as you start seeing a change in the angle or the shape of your nails, you should get alarmed and rush to your physician to check if it is an indication of finger clubbing or not. Remember, since finger clubbing is associated with an underlying disease, therefore an early detection of finger clubbing can lead to an early detection of an underlying disease and thereby can help you to start the treatment well on time, before it becomes difficult to treat.

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