Had 3x bypass. Scar near right ankle has stayed numb. Became "itichy" a few months ago. Now has spread to entire lower leg and to a lesser degree left leg. Redness, rough skin, antihistemens give some reieif. Controlled diabetic. Age 67. Very steroid se

Stasis dermatitis. Poor vasculature around a surgical/scar site likely aggravating these symptoms. A vascular person may be recommended to take care of this.
Many possibilities. There are many types and causes of skin rashes that could cause itching. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.
You . You need to have your primary doctor evaluate you. Whether this is diabetic neuropathy or ischaemic is some thing that need to be sorted out.