Diagnosis of digital clubbing by high-frequency ultrasound imaging

Current methods to diagnose clubbing have drawbacks. This study was done to test a novel and convenient method for the diagnosis of digital clubbing using high-frequency ultrasound.

Index fingers from a healthy control group without digital clubbing and a patient group with digital clubbing were examined by ultrasound. The morphology of the clubbing fingers was observed. The soft tissue depth under the nail (SDUN), interphalangeal depth (IPD), and distal phalangeal depth (DPD) were measured. The ratio of DPD and IPD (DPD/IPD) was calculated.

Nails, soft tissue under nails, digital bones, and digital joints were clearly observed by ultrasound. The mean SDUN was 0.16 ± 0.01 cm for the control group and 0.284 ± 0.02 cm for the patient group (P < 0.01). Ultrasound images were assessed by naked eye and ultrasound measurement. SDUNs in the patient group were larger than SDUNs in the healthy control group. The DPDs were larger than IPDs in the patient group, while in the healthy control group, DPDs were smaller than IPDs. The mean DPD/IPD ratio was 0.86 ± 0.04 cm in the control group and 1.077 ± 0.11 cm in the patient group (P < 0.05).

We present a new, easy, convenient method for the diagnosis of digital clubbing using ultrasound. We also discovered a new parameter for the diagnosis of clubbing fingers and identification of pseudodigital clubbing, the SDUN. The increased SDUN might be taken as an early sign of digital clubbing.