Is it possible for large breasts (G cup) to cause cervical dystonia? I had D cup, 500cc saline sub muscle implants 8 yrs ago.

The answer is yes, large breasts can certainly cause your symptoms, whether naturally large or large due to an augmentation.  Discuss this situation with your plastic surgeon.  I have had a number of patients decide to have their implants removed to reduce the weight of their breasts to help alleviate symptoms of musculosketetal strain.  Such symptoms are often multifactorial in nature, but taking some of the weight off your shoulders may eliminate one exacerbating symptom.  

Breast Reduction is routinely done for patients who are double D cups or greater and have symptoms including neck pain, shoulder pain, upper back pain and sometimes upper extremity symptoms.  Your G cup breasts would suggest that are very heavy and could be causing your symptoms.   The fact that all of the other treatments failed supports this.  You could be a treated with a removal of your implants and a breast reduction.  

Large heavy breasts whether from your own breast tissue or from large implants can exacerbate your neck symptoms. You can certainly remove or replace your implants with smaller ones. A breast lift may also be helpful with either choice if your breast are sagging as well as too large.

Thank you for your questions and I am sorry to hear of your medical symptoms.  I would counsel you to make an appointment to see an ASPS board certified plastic surgeon.  Due to the size, weight, and duration of your implants your neck and back may be straining too much and removal of the implants with a lift and possible reduction may be in your best interest.  No one can assure you that it will resolve your cervical dystonia but it is the next logical step to try and obtain improvement.  

I have no doubt that your large saline implants are contributing to your neck problems. Some of the happiest patients in my practice are women who have achieved a "breast reduction" from a simple implant exchange for smaller implants and a mastopexy. I think you should discuss this with your surgeon.