Cushing's induced myotonia

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Hello all,

I am seeking advice on management of a 10 yr old, MN, Poodle with

Cushing's induced myotonia. My boss is a DACVIM internist, he has the

Cushing's disease under control. When the dog started with rear limb

stiffness almost a yr ago, the internist recognized it right away as

myotonia and confirmed it with an EMG. He tried methocarbamol few

weeks, no help. Next he tried mexilitine at slowly increasing dosages

for 4 to 5 mos-no big improvement. In fact over the first 6 mos, dog

became increasingly spastic in the rear limbs, dog is still

ambulatory and walks like Charlie Chaplin. At first, I had the owner

doing heat, massage, PROM. Eventually, as dog became stiffly rigid in

rear limbs (stifles extended, and limbs adducted), the owner and I

could do less and less ROM. We next tried electroacupuncture (Dr.

Chrisman from UF and Chi Inst. gave me protocol-dog " felt better " ,

but didn't decrease the stiffness/spasticity.) Next we have tried

dantrolene-per some human PT contacts- at dosage of approx 1 mg/lb,

for 3 mos. The internist has been very willing to try my ideas as I

research this, I was afraid to go higher as understand dantrolene to

be poss liver tox. Also no big help. I looked into botox injections

(Kornegay, Childers), but understand that btx is for spasticity due

to UMN damage, whereas canine Cushings myotonia is a muscle membrane

problem. Am new to this list and happy to have this resource to share

info, so hoping someone with more experience in this area can make

some suggestions. Has anyone used dilantin, or procainamide, or other

suggestions for this condition? This dog is a happy little poodle,

with a very dedicated owner, willing to try new therapies as we make

these connections between vet med and human pt.

Thanks so much,

Sherry Headrick, DVM, CCRP, CVA

Associated Veterinary Specialists