Good Morning Christine, and thank you for your question.
I’m sorry to hear about your mare’s ongoing condition. As to your question about a possible viral cause, this is unlikely, however I would not rule out the possibility of an allergic reaction, although as this has been occurring for quite some time, this would also be low on my rule-out list. I’d like to ask you a few questions so we can perhaps get a better idea of the possible cause.
1): You noted that this started out as a small swelling. Where exactly was this initial swelling, how large was it, and did you notice and type of skin wound associated with the swelling?
2): Does she get any regular type of exercise?
3): Did the Bute regimen seem to help the condition at all?
4): Is she eating and drinking normally? Is she having normal urination and bowel movements?
5): How long ago did you notice that she was losing the tone in her back muscles, and has this been a drastic change?
Thanks in advance for your answers, and I’m looking forward to hearing back from you.
-Dan C., DVM.