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 Pa O 2 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 ⩾1 (>3 SD above mean from 85 controls; no history of pulmonary disease; mean age, 14.8 ± 7.6). The Pa O 2 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 < 0.0001). Digital clubbing was present in 39 of the 84 (46%) hypoxic patients (Pa O 2 ⩽ 88) but only four of the 78 (5%) normoxic patients (P < 0.0001). The DPD/IPD ratio was negatively correlated with Pa O 2 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 Pa O 2 (r = −0.53; P < 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. Pediatr Pulmonol 1991; 10:25–29.