weird bump on mouse

Question

Caramels' leg   QUESTION: My oldest mouse has recently developed a large bump on her leg, which is visible in the picture, at first i thought it was just her leg joint but because it is not noticable on both sides i found it odd. it does not seem to hinder her in any way and she does not squeak when i touch it. she has not broke her leg recently or hurt herself. it just randomly formed. all my mice were recently on tetracycline because my newest mouse had some cuts on her I do not know if it is a side effect from the medicine or if it just happened because of her old age. but like i said it doesnt not seem to bother her in the slightest bit and she uses the leg just fine, in face she is more active now then she has been in a while. is it something i should be worried about?

ANSWER: Hi Sara,

Bumps are typically one of two things - a tumor or an abscess.  It sounds bad, but abscesses are easily and quickly fixed up, and tumors are frequently scarier to us than to the mice they affect (you saw she doesn't seem to mind it much).  Tetracycline would not have caused it, in fact, tetracycline is usually what I tell people to take as a first step for keeping abscesses at bay.

An abscess is a swollen, closed-off infection that can grow large, feels squishy (be careful not to pop it when feeling it!), and would need to be lanced and cleaned by a vet to prevent the infection from bursting and infecting other parts of the body.  They don't have to be serious, but they should definitely be treated quickly.  Abscesses usually start because of an injury like a scratch or a bite - do you know if she's been injured in a small way in the recent past?  Are there any spots around the area that might show a scab or a spot of missing fur?

The second possibility is a tumor, which could have popped up now due to age and genetic factors.  A tumor will usually feel a little harder and is not usually treatable (few doctors will give anesthesia to a mouse, and in addition tumors will often come back when removed).  A tumor does not have to be a problem, however, and there are only two things you need to watch out for.  First - how fast has it been growing since it developed, or did it pop up and then stop?  A tumor that continues to grow very rapidly might start to become uncomfortable.  Remember that prey animals don't show pain until it is severe, so watch it to see if it changes and keep an eye on her behavior - she might give you hints like sleeping more, playing less, or losing or gaining weight, or not keeping her coat clean.  No change in the bump is good - but if it grows larger quickly or if she starts to slow down or act differently, you should ask a vet if there is anything you can do to help her cope better.  The second thing you need to look for besides growth and behavior is the skin over the lump.  A consequence of having a new bump on your leg is that moving is sometimes impaired, and you want to make certain it isn't being rubbed raw on bedding or toys.  Carefresh and similar paper beddings are very soft and could help if you notice the area become irritated.  Besides that, there really isn't much to be done about tumors, and mice can certainly still live happy (albeit lumpy) lives.

I know all of that sounds really ominous, but truthfully, it's not as big of a deal as it first seems.  You should definitely determine whether it's an abscess or a tumor (a vet may be able to tell you for just the visit fee), and if it's an abscess it will need lanced, but after that all you need to do is watch her and the bump for changes and make sure she stays happy and comfortable.

Hope I helped!
-Tam

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Caramels' leg   QUESTION: There is no area that feels like a scab and they are currently living in a cage with paper bedding. It kinda feels like it is in between squishy and hard it is firm but it is not rock hard i guess you could say. I have not noticed the bump getting any bigger then it currently is. i think when it started appearing it was a steady growth and it seems like it has stopped. but she is an old mouse, coming up on a year =\,  and she has had babies. but i dont think antibiotics would help because she was just on them for ten days along with the others. and there is no hair missing from the area either. so since it is seeming like it is a tumor are there any signs i should look for to know if she is in pain. or is what you have already told me the only signs to watch out for?

ANSWER: The best way to be sure which it is is to ask for the opinion of a licensed vet, which if you can, I would highly recommend because of the need to treat an abscess immediately.  It does sound like a tumor to me, but I'm no vet and certainly can't be sure.  If it's an abscess, however, you could fix her problem in one visit!  :)  A year old isn't old at all, either - she's about middle-aged.  Healthy, well-bred mice can live anywhere from 1-3 years old, so she may have a good while ahead of her!  :)

As far as telling if she's in pain - you know her better than anyone.  If she starts sleeping a lot more, moving slower or playing less, if you notice any tenderness or change in the lumpy area, if her weight changes, if her eyes dull, or if her coat starts to look uncleaned all the time - she could be suffering.  At that point it would be very important to ask a veterinarian for advice about things you can do to make her feel better, or maybe even medicines you can try.

-Tam

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QUESTION: Is there any chance that the bump could be because she dislocated her leg, that what i originally thought was wrong but it seemed odd that she wasn't acting odd so i ruled it out but is it at all possible that a lump would grow due to a dislocated leg. of course I have no clue how she would have dislocated it. or is it possible for fat composites to develop on mice? My brother seems to think it had something to do with her being pregnant before but that doesnt seem logical to me because that was more than 6 months ago. I am just trying to cover all aspects and I will try to find a vet to take her too and who i can afford. I am happy to know that she could live up to three years though I was under the impression that mice life spans were only 1 year 2 if they were taken care of very well.

Answer
Yes, it's possible that there could be some initial swelling from dislocation of a joint or damage to surrounding tissues, but inflammation would be very soft and would go down after a day or two.  Does the area feel hot?  Inflammation is always accompanied by warmth.  My guess is at this point you would be able to clearly feel the joint in question through the skin, and not a lump, if it were due to a dislocation or even a break.

I don't know much about the possibility of a sudden accumulation of fat deposits, but I do know that the area along the side of the mouse from the back leg to the armpit is prone to mammary tumors in some mice.  Mammary tumors are linked to hormones, so it may be possible that her pregnancy or subsequent cycles could have affected it, but I'm not sure.  I don't think that her past pregnancy could affect fat deposits, but once again, I'm not entirely positive.  

Hope I helped!
-Tam