Hello,
Since the patch of skin is intensely itchy, so one possibility that is coming to my mind is of nostalgia parasthetica. It also presents as itchy, dark pigmented patch seen one the back or trunk. Sensation to light touch, temperature, vibration, and two-point discrimination may be normal or abnormal.
Biopsy skin can help in confirming the diagnosis. Also if there are any other systemic symptoms, then systemic diseases like scleroderma and SLE have to be ruled out. For that you need to consult your dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I had have this same exact itch for 24 years! It comes and goes. There is no antecedent, no dry skin, no marks, except what I do by scratching. Nothing but ice stops the itch. Sometimes I need 2 -4 ice packs at a time. My mother and all 5 of my siblings also have this. Have you been able to determine what it is and how to stop it forever?
I just read your statment and I have the exact same thing and have tried everything. TOnight I grabbed Aspercream Roll On and ii'll be damned it works. It was just a fluck, but maybe it will work for you also. I'm sure I'll have to repeat but it's so worth it.