Digital clubbing is a physical finding characterized by an enlargement of the distal segment of the fingers or toes, which may or may not be associated with underlying disease states. Autopsy findings in patients with clubbing reveals an increased nail-bed thickness (greater than 2.0 mm) and a low density of nail-bed connective tissue. This is usually a symmetric and painless condition; however, cases of unilateral clubbing (brachial arteriovenous fistula and hemiplegic stroke) and painful clubbing (hypertrophic osteoarthropathy) can occur. Hypertrophic osteoarthropathy (clubbing associated with periosteal new bone formation and arthritis) is associated with pain in the joints of the wrists, ankles, knees, and elbows. This condition is associated with underlying systemic diseases especially pulmonary and extrapulmonary malignancies. Pachydermoperiostosis is a rare, congenital form of hypertrophic osteoarthropathy that begins at puberty, is more common in males than females, and is associated with multiple cutaneous changes (thickened greasy skin of the face and scalp along with excessive sweating usually affecting the palms and soles). Thyroid acropachy refers to clubbing in persons with thyrotoxicosis.
Findings consistent with clubbing include nail-fold angles greater than 180 degrees (normal is equal to or less than 160 degrees), phalangeal depth ratios greater than 1.0, and a positive Schamroth sign. The phalangeal depth ratio is calculated by dividing the depth of the digit at the nail bed (use calipers to measure the vertical width) by the depth of the digit at the distal interphalangeal joint. This ratio is less than 1.0 in disease free patients, greater than 1.0 but less than 1.05 in patients with nonmalignant disease, and a value greater than 1.05 should prompt an aggressive search for an underlying pulmonary malignancy. The Schamroth sign is assessed by having the patient place the dorsal surfaces of the digit against its matching contralateral partner. Normally, a diamond shaped window will result at the junction of the two proximal nail beds; whereas, this space will be obliterated in patients with clubbing. Another finding in patients with clubbing is the sensation of a floating nail on palpation by rocking the proximally and distally in the nail bed.
Since various organs systems can be involved with a marked range in the underlying pathology, an extensive work-up is usually not undertaken unless there are other symptoms to direct the work-up. Involved organ systems include the lungs, liver, thyroid, and vascular malformations.