mayasthenia gravis/polymyositis

Question
what is the prognosis for an almost 12 year old golden retriever? Is the treatment too much for an old dog? What would happen if no treatment given?

Answer
A 12 yr old Golden is old for a lg breed dog and s/he may only be around for a short time regardless of diagnosis and treatment.  

However, if your dog is only mildly affected, then I would suggest trying medication.  The treatment of myasthenia is to suppress the production of antibodies and to increase acetylcholinergic function. The former is usually done by the administration of prednisolone at 1-2 mg/kg/day, which is a very inexpensive medication that is tapered over time while monitoring the serum anti-receptor antibody levels. The second part of treatment is to increase acetylcholintergic function and is done by giving pyridostigmine (this medication can be quite pricey but again oral).  

During a myasthenic crisis, intramuscular injections of neostigmine (0.5-2.5 mg) may be given to your dog by your veterinarian.

If there is mega-esophagus, then subsequent aspiration pneumonia is likely to develop and prognosis if poor.