I have one arm that's about 4 inches bigger than the other? What would be the best procedure for consideration for the arm?

You need a formal evaluation by a licensed plastic surgeon and expert in arm lifting to determine what is best for you and your goals.I treat problems of the upper arm in different ways depending on the nature of the problem. For those with firm, healthy, elastic upper arm skin, I use liposuction cosmetic surgery to sculpt and reduce the size of the upper arms to match the lower arm. Once the excess fat is removed, the skin shrinks to the fit the slimmer arm underneath. Liposuction of other body areas can be performed at the same time, as needed.
For patients with loose, sagging skin under their arms (or "bat wings") due to aging, gravity, or significant weight loss, liposuction will actually worsen the appearance of the arms. To properly reshape the arms, I tailor the skin to fit the underlying arm by surgically removing excess skin and fat. This procedure is called a brachioplasty (arm lift). A "mini brachioplasty" does not offer as much improvement as a full arm lift but is an option for patients with loose skin near the armpit or arm fold, leaving only a small scar in the arm crease.
Whether I perform liposuction, a full brachioplasty, or a mini arm lift, my goal is to give patients slimmer, more attractive upper arms. I suggest consulting with a board-certified plastic surgeon and expert in arm lifting. - Dr. Cohen

Thank you for your question regarding what would be the best procedure for an arm that's about 4 inches bigger than the other. An in-person physical consultation is in order. Unfortunately, you did not provide pictures. Therefore, one can only guess that you have excess skin and fat on your larger arm. Do you have lymphedema? Since you have excess arm skin, you need arm skin removal. Since you have excess arm fat, you need arm fat removal. A combined procedure of removing arm skin and fat is a brachioplasty, arm lift, or arm reduction. The fat is removed with liposuction and direct surgical excision. Also, during the surgery, the excess arm skin then is removed. A brachioplasty is usually accomplished with an incision from the armpit to the elbow. Since your arm is 4 inches bigger than the other, the best solution would be a one-sided or unilateral brachioplasty. That would be the best procedure for you. However, you mentioned you cannot live with the long arm scar. You will get suboptimal results since you cannot live with the long arm lift scar. Since you can’t live with the scar, the second best procedure is arm liposuction to remove the fat. However, you must understand that arm liposuction will not remove or tighten the arm skin. You will be left with some loose arm skin. You mentioned even now that, you have loose arm skin from weight loss and age. Your loose arm skin will get worse with isolated arm liposuction. Therefore, most experienced board-certified plastic surgeons who do extensive arm lifts would suggest a unilateral brachioplasty or arm reduction with the removal of excess skin and fat. However, since you cannot live with the arm lift scar, VASER arm liposuction is your best second best option. However, you must understand that you will have sagging arm skin after arm liposuction. Good luck. I hope this answers your question regarding what to do with asymmetric arms with one arm being 4 inches bigger than the other.
Sincerely, J. Timothy Katzen, MD, FASMBS,  FICS
(Certified by the American Board of Plastic Surgery, President of the American Society of Bariatric Plastic Surgery)

Without knowing the reason for one arm being bigger than the other, or having photos, it is impossible to offer advice.  Suggest you upload photos or explain the medial reasons for the difference in size. Best answers will be available through an in-office consultation with a board certified PS.Kenneth Hughes, MD, ABPS Board Certified Plastic Surgeon
Los Angeles, CA