I had your symptoms a few years ago but hadn’t had a lymph node dissection on the right side, by far the worst of the 2. When it really got bothering me at night I self diagnosed myself with carpal tunnel issues and bought a special splint to wear at night. After a few months I had numbness in the thumb, index, and middle fingers. I went to my clinic and had nerve conduction studies that confirmed carpal tunnel problems. Since my right had was the worst both for me and on testing I elected to have surgery and not a steroid shot. What a difference. About 3 months after surgery all numbness was now gone but the left one started acting the same way. I elected to try a steroid shot first, relieved some of my symptoms but not all so had surgery on it as well (9 months after the other one). BTW—I too was on Letrozole at the time but never thought to ask if it was it causing my problems.