Hello I am Dr. Joey. Thanks for asking and trusting me to help you and your pet today. I am a licensed veterinarian with over 16 years of experience. I look forward to working with you.
Swollen gums and this level of pain are most commonly associated with a condition called stomatitis (gingivostomatitis). It is such an awful condition and tough to control. Rarely a cat might respond to a steroid injection as I assume has already been tried. I hope this is old news. There are many possible underlying conditions (viruses like calicivirus, bacteria like ) but it is generally an immune system response, however inappropriate, that is leading to the inflammation. There is often no one drug that makes it go away (forever) and it is tough to control. Over the years we have found very few treatment options other than tooth extraction and sometimes also laser gingival treatments.
If your vet is not sure if this is stomatitis, then biopsy of the gums is warranted (this rules out cancer as a cause). If stomatitis is felt to be the cause or biopsy proves it then,an 80% improvement has been reported with the use of long-acting steroids, megestrol acetate and Gold salt. However, there are no studies to show cats could be cured with these medications (which means repeated treatment is required), and side effects with these drugs can be significant. The current therapeutic approach to chronic gingivitis/stomatitis is to eliminate all sources of infection (extract teeth) and of chronic inflammatory causes from the mouth. There is debate amongst feline dentists on which teeth need to be extracted as some practitioners advocate full-mouth extractions instead of a more selective approach, which mostly result in extraction of premolar and molar teeth. The results of dental extraction can lead to 50–60% of cats are cured, 25–30% are markedly improved, and about 15% are totally nonresponsive. But it must be done by someone who is well versed in feline tooth extraction, has the ability to do dental radiographs (X-rays) to confirm all roots were completely removed (a residual root can cause the inflammation to continue) and very good IV pain relief. Often cats are hospitalized at least a day after this to control pain.
Until he has proper dental care and you decide what to do you need to have him on daily pain relief. Many cats use daily buprenorphine which can be professionally compounded (your vet can order this) such that it is not terribly expensive. If medicating is a problem the using a Fentanyl trandermal patch is another option (I use this around the dental extraction procedure mentioned above).
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