American Fancy Rat & Mouse Association

This article is from the Spring 2000 AFRMA Rat & Mouse Tales news-magazine.


Rat with Wrist Lumps

By Carmen Jane Booth, D.V.M.

Pat Bromberek, Portage, WI
Q I am addressing the following to Dr. Booth in hopes that she is familiar with this bacteria my rat, Smudgers, has. I enclose the biopsy report. Now I will fill you in on how this all started.

Back in early September I noticed a pea-sized lump on Smudgers left wrist. It had a core and it did abscess but the stuff that came out was not the usual “greenish,” smelly stuff. It was more like a “rice pudding” texture and no smell. It went away. Shortly after, several more lumps began appearing but now they were all over his left arm. A trip to the vet showed that these lumps were non-cancerous but bacterial in nature. His arm muscle was very swollen so he was put on prednisone and amoxicillin. The lumps did abscess and it always was a discharge of off-white cottage-cheese substances. In the meantime, the arm appeared to be improving from the prednisone. Then it started to swell up again very rapidly and the next trip to the vet was when a biopsy was taken and several of the lumps were removed. Dr. Cooper indicated that the lumps were masses of dead tissue and that they did not appear attached to the muscle of his arm. The biopsy results came back a week later, but in the meantime Smudgers was kept on amoxicillin. Also, his arm was not improving, lumps were re-appearing only on his left arm — nowhere else. In January, Smudgers had surgery. All of the lumps — some very large — were removed. We hoped this would cure him, but I was warned the lumps could come back. And they did; however, they abscessed big time and his arm looked better. In the meantime, Smudgers developed a respiratory problem and was on Baytril and Doxycycline for 21 days. His arm did not get bigger or abscess, but small, new lumps were forming.

Where we sit on this now is I believe this bacteria has invaded the lungs. He is no candidate for a second surgery (Dr. Cooper suggested an arm amputation) which would be a last ditch effort to end this. I noticed a fissure on the inner part of his forearm the past 2 weeks since the last time it abscessed quite heavily. How is Smudgers taking this all?? He has no problem getting around. Now I fear that with his lungs not well, this could do him in. He is a year old, and he is back on amoxicillin.

Have you ever come across a case like this? Even if Smudgers succumbs to this, if there is an answer to treating and curing this should it happen again, another rat could be saved. By the way, does this same bacteria cause bumble foot? Back to Smudgers case, Dr. Cooper said a bite possibly caused the onset of his problem. (He was living with Moley but they never fought; at least I NEVER saw them fight). In fact he is back living with Moley again since his arm healed from the surgery because he got so depressed and they both are fine together.

I hope you are able to find an answer to this. I included the lab report to help you possibly make something out of this. I have had rats 14 years and NEVER have I come across this bizarre case. Just when you think you’ve “seen it all” something else crops up!

P.S.: His breathing has not improved, even when he was on Doxycycline and Baytril (this combo works well for me when my rats have the usual respiratory problems). This is why I believe this bacteria spread to his lungs. Also, the substances that I drained from the abscessed lumps never had an odor, and never has the usual greenish thick substance like most abscesses. I found this odd.

Department of Agriculture, Traid & Consumer Protection
6101 Mineral Point Road Madison, WI 53705-4494

Diagnostic Final Case Report

Date Received: 29-Oct-99


Species: RODENT
Accession Number: 752158


Animal ID: Smudgers

SPECIMEN: Fixed Tissues
The masses are from the right front leg.

Skin/Mass (Circumscribed-Encapsulated-Expansile)
Chronic active multifocal suppurative dermatitis

This section is characterized by multifocal abscesses containing cellular detritus and inflammatory debris including multifocal intralesional stelliform aggregates of eosinophilie material associated with a radiating corona of clup-shaped bodies at the surface (Splendore Hoepli reaction).

The special stains reveal variably aced fast material and bacteria, no fungal agents, and variably Gram-positive/negative coccobacillary bacteria.

The histopathological findings are compatible with a chronic suppurative disease process involving a bacterial agent. The nature of the agent, as indicated by the staining pattern, suggests a Corynebacterium kutscheri (muris) agent.

The prognosis for this case in uncertain.

Stephen P. Schmidt, DVM, PhD, ACVP
Veterinary Pathologist

Fax Contacts/Finalized: November 7, 1999

A Thank you for history and inclusion of the pathology report. I would guess that Smudgers is an older rat, perhaps over1.5 years-of-age? This is a very unusual presentation. I am concerned that Smudgers has some underlying condition that has lowered his immune system. Cancer, diabetes, and old-age can all lower the immune system. If he is a younger rat, than he may have some innate problem with his immune system. It is very perplexing. The bottom line is that the bacteria need to be killed. Corynebacteria spp. can be very difficult to treat. My suggestion would be to culture some of these lesions (the report suggest a mixture of bacteria) and have a sensitivity performed. This way you will know exactly what bacteria are growing and what will kill them. Do not give any more steroids, it just makes it more difficult for Smudgers to fight off the infection. Since he is on antibiotics already, it may interfere with getting an accurate bacterial identification and sensitivity. He may have to go without the medication for 2–3 days in order to do an accurate culture and sensitivity. You do not have many options, Baytril and Tetracycline are both good antibiotics, but if the bacteria are not sensitive to them, then Smudgers will not get better.

In the future, if anyone else has a rat or mouse with these symptoms, ask your veterinarian to collect some of the tissue for a culture and sensitivity (C&S) at the time of the biopsy. This way if it turns out to be tumor (quick turn around), the C&S can be discarded before the sensitivity is performed. In difficult and persistent bacterial infections, a culture and sensitivity is one of the best options for determining the antibiotic therapy. *

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Updated April 10, 2014