A Presumptive Diagnosis? 8-8-09

Post date: Aug 8, 2009 9:04:46 PM

Just when Rowan seemed destined to remain a medical enigma, our on-vacation neurologist called in a prescription for prednisone. Presumably he received Rowan's muscle biopsy results and agreed with the lab that even though Rowan was negative on the masticatory muscle myositis (MMM) test and even though his atrophy is only on one side, MMM was still the most likely diagnosis.

I don't know how they distinguish between trigeminal neuritis (the idiopathic version that resolves on its own--no prednisone required) and MMM. Yet here we are. I don't know how we'll ever know for sure now if Rowan has MMM. Now that he's received prednisone, it will skew the results of future tests.

I picked up the dreaded orange pills from Rite Aid last night. It's hard to imagine Rowan being hungrier and more food-obsessed than he already is (insatiable hunger is one of the common side effects of prednisone). I just gave him his first half pill with a sinking heart. To treat an auto-immune disease like MMM, you have to give a strong enough dose to beat back the immune system. It's nasty stuff. But if you don't get on top of MMM as quickly and aggressively as possible, you risk ending up with a dog that spends the rest of his life on a feeding tube, because he can't open his mouth. So taking a "wait and see" approach is not an option.

Hopefully the prednisone will send the problem into remission and it will never come back. Yes, I feel like I've stumbled into an alternate reality where I'm a weekly guest star on the canine version of "House."

You know you're in trouble when the pharmacists at Rite Aid start asking you about your dogs, because the only time you go in there is to pick up exotic, expensive medications for your pets.

Update (8-10-09)

I talked to one of the other neurologists at the Animal Care Center today, since Dr. Westworth is still on vacation. Since we don't have a definitive diagnosis and since prednisone is such a heavy duty drug, I had a lot of questions:

• Why do we think it's MMM? Because both the MRI and the muscle biopsy showed presence of muscle disease (i.e., inflammation). Even if it's not MMM, it has the markings of an auto-immune disease, so prednisone would still be the treatment.
• Why don't we think it's trigeminal neuritis (the benign idiopathic disease that resolves on its own)? It would look different. TN is a loss of the nerve supply; TN doesn't look like muscle disease. The nerve tested normal.
• Could it still be an infection, in which case suppressing the immune system will make it worse? Yes, but it's unlikely given that there are no other signs of infection and no known infectious agent (plus Rowan's bloodwork was normal). But we should still watch Rowan carefully for any signs that things are getting worse--pain, spreading atrophy, stiffness, difficulty walking, etc.
• How long will Rowan have to be on a megadose of prednisone? Probably 2 months, then he'll have to taper off. If he tapers off too fast, he's at risk of relapsing.
• Will Rowan's head ever return to normal? Maybe, maybe not. It depends on the dog.
• How will we ever know if he's better, considering that his titer test was negative and his muscle may never return to normal? She agreed that it would be hard to tell, but the main thing is that he doesn't relapse. She also said that she still gives titer tests to dogs that have had prednisone. It's not a foregone conclusion that the test becomes worthless once the dog has had pred.

So there we have it.