I currently have an impressive set of DEEP Beau's lines on the thumb and index finger of my left hand. They are now about halfway up my nail, which would correlate with trauma to these 2 fingers approx 12 weeks ago, when I slashed the webspace of my left hand rather deeply with a large chef's knife. (a nasty kitchen accident...)
I severed the digital artery (and nerve, as well as a couple of muscle bellies..)so the nail bed blood supply to those digits would have been interrupted for some time until the plastic surgeon did wonders with his operating microscope!
They are usually the result of some sort of trauma that disrupts blood supply - either a direct force or maybe an altered state - did you have a fever or major flare some time ago??? The nail grows @ 0.1 mm / day, so 1 mm for every 10 days or 1 cm after 100 days.
They aren't usually pathological, so are of no diagnostic value....
