18 mo old male PWD diagnosed with immune-mediated polyarthritis Questions

Hello - I'm new on this board but not new to Porties. Corky is our fourth, my wife got her first Portie in 1995.

Corky has been a pure (well, maybe a little tainted ) delight. He's big (68 lbs, and skinny) and sweet and above all, playful. He loves people and he LOVES dogs, and has been healthy as a horse since we got him.

Last week Friday morning he wouldn't get up all morning so I let him sleep in (I work from home). Finally at 11 AM his dog walker came over, and he hadn't moved from the spot he'd slept in. He couldn't walk, and he could barely stand! Yikes!!! He spent all day friday and then all day saturday at the vet. No tests were positive. Although he seemed to have a painful front left leg, his joints weren't hot or swollen; no fever. The night before he'd been playing and jumping like the crazy athletic puppy he is, 100% joy and energy.

The vet was pretty stumped. There is Lyme disease here where we live in Northern California, but he's been on tick and flea prevention his whole life. And now we've done the lyme tests and he's negative for tick-borne diseases.

Ultimately he's been diagnosed with immune-mediated polyarthritis and is being treated with an immune-suppressive dose of prednisone and a low dose of doxycycline as an addition anti-inflammatory. Within 72 hours he had improved 50%, though now he's stable there.

The weird thing is, all his play-drive is completely gone. He's gone from the dog who wanted to play 24/7 to the dog who has no play in him at all - and frankly, for him it's like his whole personality and puppyhood is gone. I think this is probably a result of the prednisone, a known and common side effect is fatigue. I am less suspicious of this being caused by the disease. In fact, the diagnosis is such a vague one - it's not as if there's a black and white diagnostic test - I'm not 100% convinced that he even has the disease.

Anyone have experience with side effects of prednisone treatment (he's been on it less than a week, he definitely has the constant drinking and peeing side effect) or with IMPA? I haven't seen that PWDs are susceptible to this disease. Mainly I'm wondering about his losing all interest in play.

Thanks!!

Our Portie history:
Tashmoo, 1994-2000, died of glomerulonephritis
Buster, 1998 - 2013, died of old age, never sick
Daisy, 2003 - 2014, died of pancreatic cancer, born with health problems but healthy her whole life
Corky, Aug 5th 2014, big fun healthy boy till a week ago

Attached is a photo of our boy from June 2015, helping me garden by pulling weeds and then running around like a madman with it in his mouth - then lying down for a classic photo

i`m sorry to heat this news about your boy, sorry cant help regards the medication, just a thought though, has your vet considered "Addisons" has he tested for this, I presume given your length of time owning the breed you would know it can be in the breed.

Worth a consideration of you are not sure about the diagnosis.

BTW.... hes lovely, always nice to meet another portie owner !

Sorry I can't offer any advice/help has no nothing about the breed [Portuguese Water dog].

Sorry to hear about your boy.
What tests were done to confirm immune-mediated polyarthritis ?
This might be a long shot but some of the symptoms you describe are similar to Pano
http://www.vcahospitals.com/main/pe...rticle/animal-health/panosteitis-in-dogs/1051

Thank you. If it only occurs in a rapidly growing dog that rules it out in Corky, he isn't growing anymore. Though the rapid onset fits.

Negative tests: complete blood count, blood chemistry, joint tap (synovial fluid), lyme screen, body temperature.
Today we're doing an ANA to check for Lupus, and a repeat of the CBC/Chem.
So far no tests strongly indicate IMPA - it's just that there are no positive tests for anything, so this is a presumptive diagnosis.
Frankly, nothing is certain except that there are signs of generalized inflammation, and some signs of joint inflammation/pain - plus his initial symptoms which are difficult to interpret.

What a lovely photo. I'm sorry to hear about Corky's health problems, I hope you are able to trace and treat the source of his illness soon.