I got my horse July 31st, 2011. She is a 12 year old Arabian mare. The trainer she was ridden by moved to the barn I was at. I noticed a small lump under her skin on her back left leg. It is on the inside and more towards the top. It has hair but a small area in the middle does not and looks a little like a scar (the skin is not smooth in the middle.) I asked the old trainer about it and she said they had it examined and I think she told me they did an ultrasound on it. She said that the vet said that it could just be a cyst or something and that as long as it stays dettatched from the musle and the same size, it is fine. Well, it seemed fine for months. A couple of weeks ago I thought it may have gotten a bit bigger but I didn't think anything of it. Today, I looked at it and it is at least 3X its original size and hard (I can't remember if it was hard to begin with.) As soon as I got home I contacted her vet and asked her if she should look at it. She told me to cold hose it and that if it makes her lame or starts to look scary, then she should look at it. After it growing that much in just a matter of weeks though, it scares me and I can't help but be worried.
It is summer right now and pretty hot here in Ohio. Could the heat be affecting it? It did not last summer so I am not sure. I have looked at picture of sarcoids and it doesn't look scaley like they look in the pictures. She is bay. I know that something like 80% of grey horses have melanomas. I know that it is possible for any horse to get one but it is more likely for grey horses to get them.
What could this lump be? Any and all help is appreciated.