I recently posted a question of "my sister large crack in the middle of her nail" I have found out this is called Median Nail Dystrophy. I thought you may find this interesting as i had never seen it b4!
The condition was first identified in 1928 and is similar to habit tic disorder or onychotilloma. If a client's fissure seems to begin at the cuticle, an unconscious habit of rubbing or picking at the proximal nail fold area may be the cause. The more nervous the person, the more she'll pick, worsening the situation to the point that the habit can permanently injure the nail matrix and produce an abnormal nail plate.
Although the majority of research points to a nervous habit as the main cause, additional causes for median nail dystrophy can be other types of trauma. Tight shoes could be to blame for splits on toenails. There's a possible connection to carpal tunnel syndrome as well as to certain kinds of microbes. Dermatologists also have reported a correlation between median nail dystrophy and inflammatory conditions such as eczema and psoriasis. While some injuries to the nail root can be caused by a fungus, this usually isn't the case with median nail dystrophy.
Once median nail dystrophy appears, it can take months or years for the nail to return to normal, and recurrence is typical. When a split does heal, it's often replaced by a ridge.
my boyfriend has psoriasis and he has weird nails! One of his thumbs has a large split at the top of the nail and he has loads of funny little dents in his nails...looks as if he has been hammering metal nails into them and pulling them out :?
I have seen this before!! I used to (along time ago) do a mother and daughters nails. On both of their right hands, the thumb nail looked just like this BUT, the nail hadn't actually cracked but it did have that wacky kinda 'zipper' look down the middle. :? Turns out BOTH of then had this mad habit of using their index finger and constantly 'rubbing' down the thumb nails (I mean they both did it all the time)! :?: So, I actually overlayed the thumbs with a thin layer of Retention+ and although they both still had their habit, this time they were rubbing the coating and not their actual nail!! Amazingly enough, 3-4 weeks later, BOTH thumb nails started to grow back perfectly normally - seriously, not a mark!!! So hopefully with my little story I have maybe helped you in some way!!