Digital clubbing and pulmonary function abnormalities in children with lung disease

Digital clubbing and pulmonary function tests were measured in children, adolescents, and adults with chronic lung diseases to determine pulmonary function correlates with a quantitative measure of clubbing. The group had a mean age of 13.8 +/- 6.0 (SD) years, mean PaO2 of 81 +/- 21 mm Hg, and mean FEV1 of 60% +/- 26% predicted. Digital clubbing was diagnosed in 43 cases when the distal phalangeal depth to interphalangeal depth (DPD/IPD) ratio, measured on a finger cast, was greater than or equal to 1 (greater than 3 SD above mean from 85 controls; no history of pulmonary disease; mean age, 14.8 +/- 7.6). The PaO2 of patients with digital clubbing was 69.4 +/- 2.1 (SEM) mm Hg compared with 88.3 +/- 1.3 mm Hg in those without digital clubbing (P less than 0.0001). Digital clubbing was present in 39 of the 84 (46%) hypoxic patients (PaO2 less than or equal to 88) but only four of the 78 (5%) normoxic patients (P less than 0.0001). The DPD/IPD ratio was negatively correlated with PaO2 in subjects with cystic fibrosis and interstitial fibrosis. Weak negative correlations were seen for all other subjects except asthmatics. Overall, the DPD/IPD ratio was significantly correlated with PaO2 (r = -0.53; P less than 0.0001). The DPD/IPD ratio was correlated with other lung function abnormalities (increased RV, decreased FEV1, and FEF25%-75%) only for the subjects with cystic fibrosis. We conclude that digital clubbing is associated with hypoxemia and airway obstruction. The relation is seen most clearly in subjects with cystic fibrosis, possibly reflecting the prolonged duration of hypoxemia. Digital clubbing is rarely seen in normoxic subjects.