Hi there and thanks for your question.
What you have described certainly sounds like an "elbow hygroma". These are relatively uncommon but when they do happen they are usually on large breed dogs.
The good news is that these are not painful and they almost always go away on their own. The bad news is that it can take several months for them to go away.
Every time I see one I have owners who are begging me to do surgery and remove it or open it up. However, the experience of vets who have done this shows us that interferring with the hygroma usually makes it worse.
The best thing you can do is to encourage him to stay on soft surfaces. You can actually make a padding for the elbow but it is very difficult and I have never had a client be successful with it!
And, as far as the classes go, this hygroma are absolutely no reason to keep him away from class. You don't need to restrict his activity at all.
If you do think that this is bothersome to him or he really is acting more lethargic than usual then you should have your vet examine him just in case this is swelling due to an injury of some sort.
I hope this information helps! If you have more questions regarding this problem, just hit reply. If I am online I will respond right away. Otherwise I will respond as soon as I come online again. Or, if my answer is sufficient, then please hit accept. Thanks!
Dr. Marie.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.
Veterinarian
Compassionate licensed veterinarian with >20 years experience with cats, dogs and pocket pets