My Boxer (Struddell) got full blown DM at 8.5 she couldn't walk for the last 2 yrs of her life. We took care of her 24/7 for two years but I had to let her go in Nov of 2013.
You can do a titer test, results would at least give you grounds for a good argument.
Blood Test for Dogs to Test Immunity; Don't Over-Vaccinate! | Truth4Dogs
I'm Gunther over here more info on and sources for DM:
Thatcher has DM. Anyone use Dwanecart wheelchair? - Page 6 - Boxer Board
And if I can ask what did the DM test cost where you are?