The 'PDA nail': traumatic nail dystrophy in habitual users of personal digital assistants.

All-in-one devices with mobile phone, web browser, and organizer are now owned by over 6 million people and their popularity is increasing. These devices are often called personal digital assistants (PDAs) or 'BlackBerry(R)' devices, after a popular brand name of these appliances. The use of PDAs is associated with exposure of distal thumbs and nails to repeated pressure with a frequency of up to a few thousand times per hour and several tens of thousands of times per day. We describe two cases of traumatic thumb nail dystrophy associated with using a PDA keyboard for several hours per day. Both patients developed median nail plate dystrophy after 4-8 months of habitual PDA use. One patient also developed thumb nail psoriasis and paronychia. All symptoms resolved a few months after discontinuing PDA use. Analysis of nail biomechanics, performed by using a finite element fingertip model, showed that maximal stress reaches approximately 3 MPa and appears near the root on the internal surface of the nail, while it reaches approximately 2 MPa and appears around one-third from the root on the outside surface. In conclusion, biomechanical stress resulting from overuse of PDAs may result in various types of nail dystrophy. We suggest the general term 'PDA nails' for these nail abnormalities.