Hello I am Dr. Joey. Thanks for asking your question 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.
I am sorry to hear Lola is experiencing this. Sounds like your vet is doing all the right things to try to find out why. My one question is if she was screened for tick-borne disease (especially Anaplasmosis and Lyme disease). If not, then with the lymph node swelling I would highly recommend this as a next step. As well, screening for fungal diseases, if there are any in your area is also appropriate.
Could this be due to inflammation in the joints? Yes, it could. Your vet did a great job getting joint samples to look for this inflammation which would not show up on X-rays by doing a joint tap. This makes it less likely to be just joint inflammation. Hip dysplasia can cause pain/lameness and would have been seen on the X-rays (hopefully they were reviewed by a board certified radiologist and if not, then this is another good next step). I would also recommend having an evaluation of her spine/back to ensure no spinal lesions. This can be easily missed but can cause the symptoms that are being seen. If she has neurological deficits and nothing seen on screening X-rays then referral to an orthopedic specialist or neurologist is in order to have advance imaging such as CT or MRI to look for soft tissue issues.
The other thing to think about is this could be a neuromuscular disease or a problem in the muscle such as myasthenia which can be screened for via lab testing and/or muscle biopsy may be helpful.
I am at a point I need to know what questions you have. I hope that the information I provided has been helpful.
Please let me know if for any reason you need further clarification, have more questions, or were expecting a different type of answer.
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