Clubbing nails
Idiopathic or primary clubbing is rare, while the occurrence of secondary clubbing depends on the underlying disease.
Primary digital clubbing has been reported to occur in 89% of patients diagnosed with pachydermoperiostosis. This syndrome most often occurs in young males.
Of patients with idiopathic pulmonary fibrosis, 65% have clinical digital clubbing. In these patients, an increased occurrence has been shown in patients with higher grades of smooth muscle proliferation in the lungs.
Clubbing has been reported in 29% of patients with lung cancer and is observed more commonly in patients with non-small cell lung carcinoma (35%) than in patients with small cell lung carcinoma (4%).
Digital clubbing was reported in 38% of patients with Crohn disease, 15% of patients with ulcerative colitis, and 8% of patients with proctitis. Clubbing was observed in up to one third of Ugandan patients with pulmonary tuberculosis. It was not associated with stage of HIV infection, extensive disease, or hypoalbuminemia.