This article is from the Summer I 1998 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M.

Pat Bromberek, Portage, WI

Thank you for answering my letter regarding “Caved In” look in rats, and Reddy’s problem. I am happy to report Reddy is doing well, not having any of the problems he was experiencing for nearly 2 months! Also, he had a tumor removed from the left side of his throat about 1½ months ago. We nearly lost him during surgery, but he did come through it okay. He healed well and there have been no post-surgical problems. We were hoping this tumor was causing his problem, but this was not the case. He had at least two incidents. We keep our fingers crossed that he won’t have these again, but if it is from eating, which seems apparent, I’m sure they will occur from time to time. Also, since everybody here is mycoplasma positive, this also adds to this problem of his. We are not sure how old Reddy is, but we’re guessing about 2 years. We got him in July of ’96 and he was fully grown. The head-tilt which he has had, started in September ’96 and has had it since. He had adjusted well with this. We gave Baytril injections and prednisolone steroid which helped him but he never recovered 100% in that his head is slightly tilted, but he is active and appears happy.

My next question is for Dr. Booth. This recent health problem is one that I nor our rat vet, Dr. Cooper, has ever encountered before. Perhaps you have come across the following since you deal with rats a lot more in the medical area than we do.

Q Pep-Boy was a Hairless rat, one from a lab that are referred to as “fuzzys.” They are hairless except they have a “fuzz” all over their pink bodies which feels like “peach fuzz” to the touch. They are pink-eyed and have curly whiskers. I know these guys are prone to tumors and abscesses and bumble foot, otherwise they are quite hardy rats. I’ve had and presently have fuzzy rats here. Pep-Boy’s problem began in March when I noticed him not as peppy, but he ate well and was otherwise normal. He was about 1 year old. Several weeks later I was holding him and I felt a hard marble-sized mass deep inside the area of his abdomen and hind leg. It didn’t feel like it was attached to anything so I decided to wait a couple of days to see what direction this “thing” would take. About 5 days later I noticed that the area this thing was found started to look “puffy,” but when I palpated this spot, the growth had broken up in pieces and the puffiness sounded squishy when I pinched it together. He also started to lose weight. I got him down to the vet, and he thought it might be a lymphatic problem, possibly cancer because the cells he extracted from the puffy site looked suspicious. He had surgery April 2. When I went to pick him up, Dr. Cooper was out on an emergency call so I didn’t get a chance to ask what he found, but Pep-Boy looked fine. The next couple of days he appeared to do well recuperating, but he did sleep a lot. I was not too concerned. His incision was healing properly—no signs of infection present. About a week later I noticed the area where he had the surgery started to look puffy again. He also began to eat less and was losing weight. He still slept a lot. Back to the vet. Ten days had passed since the surgery, and I had a chance to ask Dr. Cooper what he found. (He was on vacation so I didn’t have a chance to ask him till I took him back because it was his first day back to work.) He said when he opened Pep-Boy up he was not expecting to find what he found. There was no fluid in the area—the entire abdominal wall muscle was all dead tissue so he removed it all. The marble-size mass that later broke up was scattered in the area and was removed as well. He said he never encountered anything like this. As for the present problem, the swelling again could be that it is a type of cancer present in the site. He was losing so much weight. At this point we could wait a day or two and see if it (the puffiness) gets bigger. The incision was completely healed and there were no signs of any infection ever. I left with the gut feeling he would not get better. He began to feel “cool” to the touch, but he still didn’t eat very much. I had a heating pad underneath his cage to keep him warm and conserve his energy. On April 15 he stopped eating. On the morning of April 16 he died in my arms.

I know this is a difficult one without actually seeing this in person. My feeling is that it was a type of cancer.

Thank you for looking into this case.

A Without having seen Pep-boy, I can’t be sure, but if he was a “hairless” rat, than he was also immune deficient. This means that he would be susceptible to infections from bacteria and fungi that a normal immune competent rat would be able to fight-off. The fact that the abdominal wall was necrotic (dead tissue in a living animal) and part of the area was crumbly suggests that the tissue was partially mineralized. When tissue dies, there frequently are areas of mineralization which would appear crumbly on visual inspection. As far as there being a neoplastic process (cancer) at that site, it is less likely since there was no enlarged mass of tissue present. Since he felt cool to the touch, I would suspect that he may have had a problem with his heart and circulation, which frequently leads to vascular (blood vessel) problems where blood flow is stopped or decreased. This may have been the underlying problem that caused the large area of abdominal wall necrosis. Older animals with heart problems that are stressed for any reason frequently die two days (36–48 hours) after the stressful incident. Without taking radiographs (X-rays) it is very difficult to diagnose cardiovascular disease in rodents. It is likely that because of his age, that he had a pituitary tumor, which do not usually metastasize (spread). But this is all just supposition, based on my experience and training as a veterinarian and pathologist.

This story brings up a good point. If you really want to try to find out why an animal died, than a necropsy (veterinary term for autopsy) should be performed and the tissues examined microscopically by a veterinary pathologist. As I approach the end of my pathology residency, I have come to realize the importance of doing a complete necropsy when the cause of death is unclear. I have had veterinary clinicians only send in a couple of tissues where they thought the main problem was, only to have to tell them that all the tissues were normal and not be able to provide them with the answers that they and the owner of the pet were seeking. On rare occasion, there have been times where the exact cause of death could not be determined by examination of the tissues microscopically.

To get the most information from a necropsy, the remains should be placed in formalin as soon as possible. If the remains cannot be put in formalin within a short period of time, then they should be put (in a plastic bag) in the refrigerator (not the freezer), until the next morning. The longer the tissues are left unpreserved by formalin the less likely a diagnosis can be made. After about 36–48 hours, the tissues are frequently too autolyzed (rotten) to be examined microscopically. All veterinary hospitals have formalin, and as long as the thoracic and abdominal cavities, and calvarium (skull) are opened to allow the formalin to preserve the tissues, than the remains can wait forever to be examined microscopically. It is important to have a ratio of tissue to formalin of 1:10 for proper fixation.

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