Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
This lesion may be caused by an injury that you may not be aware of or it could be other issues.
There are couple other things that this can be and your vet will have to biopsy this area to know for sure. One is an Autoimmune condition called Lupus which will respond to steroid treatments. The other is a condition called Collie Nose or Nasal Solar Dermatitis that is caused by a photosensitization and will require sunblock. These are not serious but uncomfortable.
here are a couple sites that explains in more detail: LINK LINK
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If this continues to spread on Liadh's nose, have your vet examine this to be sure that treatment is correct.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, Dr. Loretta