Hi Voltaire,
There are many possibilities here. Changes in the pulse in response to particular acupuncture points can help you sort things out.
It sounds like a February or March onset, given the timing mentioned above. If so, then XCHT is a consideration. Since it is very refractory, you'll want to add 12g Gui Zhi and 15g Bai Shao granules to the Nat Path version of the formula. It addresses deep unresolved spinal cord inflammation. Use this if the pulse responds to GB points and is deep, full and strong to begin with.
If the pulse is almost non-palpable, or profoundly weak, and it responds to BL 20 tonification, use Bu Yang Huan Wu Tang
If the pulse is thin and toned, pr conversely is superficial and buoyant, then Du Huo Ji Sheng Tang should be considered given the breed, particularly if BL 40 (sedation) improves the pulse.
Those are just a few ideas to get you going. If you can provide more specifics, that will help me help you
Steve