My pet mouse, Dora, has a lump on her shoulder with a little one next to it, at first we thought she had hurt her shoulder but she doesn't seem to be limping and will let me touch the lump without her flinching, please help!

Hi Chloe,

Lumps could be caused by several different things, and it can be very hard to determine which is the cause without a vet's help.  If you have a veterinarian in your area who works with mice, I would recommend bringing her in so he can let you know if anything can be done to help her lump.

Lumps in mice are usually, but not always, caused by either an abscess or a tumor.  Another potential, but less likely, cause is edema - a collection of fluid resulting from a injury, which would feel very watery and will dissipate naturally.  An abscess is an isolated infection and swelling that can result from an injury or scratch that gets bacteria in it.  This may go away on its own, but the best bet to prevent a systemic infection and illness is to have a vet professionally lance it and provide antibiotic care.  A tumor can be tough to tell from an infection, but even though it sounds scary, is actually less dangerous.  Tumors in mice rarely spread and don't hurt - they just look a little funny!  The biggest thing to watch for with a tumor is to keep an eye on how quickly it is growing, and if it causes any impairment to mobility.  If it starts to get irritated from rubbing against things, or starts to bother her, it is time to talk to your vet to see if there is any way to help her comfort level.

It's great news that it does not bother her when you touch it.  How quickly did the lump form?  Is it still growing?  Is the skin around it in good condition?  These are all things to consider when trying to figure out what the cause is and how to address it.  Again, if there is any way for you to get her to a veterinarian, that would be your best move, hands down.

Let me know if there is any other way I can help!


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I can answer questions regarding mice as pets, mouse behavior, color and coat genetics, breeding techniques, and general health questions. I can help with caging and setup, nutrition, social issues, and what to do in most mouse emergencies (such as unplanned litters, injuries, fighting, etc.). I can also assist with questions pertaining to orphaned mouse pups, weaning litters, and questions of mating and birthing. I cannot answer questions about exotic or wild varieties of mice such as spiny or pygmy mice. *****FOR EMERGENCIES, anything requiring immediate medical intervention, PLEASE take your mouse to a professional veterinarian or wildlife rehabilitator who works with mice as soon as possible! IMPORTANT RESOURCES: Raising Orphaned Mice: http://www.rmca.org/Articles/orphans.htm Orphaned Mice Videos: http://www.youtube.com/user/CreekValleyCritters/videos?query=raising Natasha's Your First Mouse: http://www.youtube.com/watch?v=RNK4uqNZTbA&feature=share General Mouse Help: http://www.fancymice.info/ Mouse Info and Exotic Breeds: http://www.hiiret.fi/eng/species/


I have enjoyed the companionship of mice nonstop since 2004, and spent a year caring for them in a lab where I learned a great deal about their breeding, social needs, and health. I spent a few years breeding them, specifically working with albinos, marked mice, angora mice, and satins. My education never stopped - I am learning something new every day from current and well-established research thanks to the wonderful folks at the Jackson Laboratory, as well as from my wonderful mousey friends online. I also love learning from my terrific questioners here on AllExperts - you folks keep my passion for these amazing animals alive and well!

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