What commonly causes clubbing?

Clubbing is a condition characterized by the enlargement of the ends of the fingers and toes, often associated with a variety of chronic respiratory and systemic diseases. The primary mechanism behind clubbing is related to chronic hypoxemia, which is a decreased level of oxygen in the blood. When tissues are deprived of adequate oxygen, there can be compensatory mechanisms that lead to the proliferation of tissues in the distal phalanges, resulting in the characteristic shape change that is observed in individuals with clubbing.

Conditions that lead to chronic hypoxemia, such as various types of lung disease (such as pulmonary fibrosis, lung cancer, or chronic obstructive pulmonary disease), can trigger the vascular changes and increased growth of connective tissue, ultimately causing clubbing. This link between low oxygen levels and clubbing has been well-documented in medical literature, making it the most recognized cause of the condition.

In contrast, other factors listed, such as fluid overload, infections, or hydration status, do not have a direct or commonly accepted causal relationship with the development of clubbing. Fluid overload may lead to swelling but does not cause changes in nail shape. Infections in the respiratory system can sometimes be associated with clubbing, but only if they lead to chronic hypoxemia.