The reason for the swelling may be twofold. Both his work on the computer and piping may cause the repetitive stress (and strain) syndrome, which manifests as swelling and pain. The same strain on the hand may cause arthritis. For the syndrome there is specific orthpedic gear. Arthritis is a bigger and more comprehensive problem. To alleviate that there are cortizone injections, low-acid diet and joint strengthening supplements, although I don't know if they are as effective, as they claim! If the pain and swelling are severe and don't diminish, he should definitely see an orthopedist. Wishing you health!