Dog started thyroid meds, huge improvement… now X-ray shows possible lesion…

Hi everyone, I’m just a nervous dog owner looking for some general insight while we wait on a radiologist report.

About a year to a year and a half ago, my dog (7 Y/o aussie/collie/retriever mix) started gaining weight and becoming really lazy. We assumed it was just age or lifestyle. Around spring/summer last year she also developed a limp in her front leg that was worst when she first got up, but usually improved after walking for a bit. Our vet thought it was likely arthritis made worse by her weight.

We tried weight control food and lowering calories, but she kept gaining weight anyway. By Dec/Jan she had gained about 10 lbs and the limp was getting worse. Bloodwork in January showed hypothyroidism, so she started levothyroxine on Jan 16.

The change was honestly wild.

Within a week she had way more energy.

Within two weeks she was playful and running again.

By about three weeks her limp had mostly gone away, and she even ran about a mile with me.

She’s since lost about 10 lbs and overall acts like a totally different (younger) dog.

Recently though she’s also had:

• Lots of panting
• Restlessness/anxiety and pacing
• Not wanting to eat her regular food (but still eats treats)
• Pretty rapid weight loss

Yesterday her thyroid levels came back “in range,” but because of the history of the limp they did X-rays and mentioned they might see a lesion near her wrist, so they sent it out to a radiologist.

What’s confusing (and scary) is that clinically she seems great: she’s active, playful, lets me touch and move the leg without any pain, and her limp has actually improved since starting the thyroid meds.

I’m not looking for a diagnosis here, just some general context:

• Is it common for thyroid treatment + weight loss to dramatically improve arthritis-type limping?
• How often do X-rays pick up degenerative or benign changes that initially get called a “lesion” until a radiologist reviews them?
• Do panting/anxiety/appetite changes sometimes happen if thyroid meds are a bit strong, even when labs look normal?

We’re waiting on the official radiology report, but I’m having a hard time not spiraling. Any general insight would really help. Thank you.