Cat and blue skin, continued.

Question
Dear Dr. Huang

A little while ago, I asked you about my cat Mystery, whose injured skin had turned blue. You told me that it was probably cyanosis caused by damaged blood vessels.

I have been thinking about your diagnosis, and I do not think that is what is happening here.

First of all, I Googled pictures of cyanosis. From the photographs, I gather that cyanosis causes skin to turn purplish. Mystery's affected skin is deep blue, almost cobalt. My mom, who is a nurse, also said that it didn't look like cyanosis.

Second, I do not think her skin is more damaged there because her hair is growing back thicker in the blue spot. Since I last wrote to you, show has started growing a thick thatch of jet-black hair in the blue area, while the pink skin has has thinner-looking, muted greyish hair. (Mystery is black on top, but her hair has lighter roots. She looks completely solid black, though).

I realize that Internet diagnoseses are imprecise at best, but do you have any new insight into Mystery's mysterious color?

Answer
I have been researching and have yet to find a specific process to describe why the change and such drastic darkening of the skin in the region.  It is often seen with chemotherapy, parasites or even clipping for surgery that the hair that regrows in the area may take on different characteristics.  While it may be of different color than the original, it may also be thinner or coarser in texture.  I am sorry that I have not been able to find an adequate description of why the skin has turned the shade it has.  If it no longer appears to be healthy I would recommend having her seen by your veterinarian.  Otherwise it sounds as though he is healing well, with a new quirk of coloration.

Have a lovely day and best wishes to you and your feline friend.