You have developed dark patches over your back....this can be a presentation of Macular amyloidosis...
Macular amyloidosis is a cutaneous condition characterized by itchy, brown, rippled macules usually located on the interscapular region of the back and then involving the whole of back..
This condition can be associated with some degree of itching...but any kind of itching or massaging the lesions can increase the lesions...so one has to abstain from rubbing the area. topical steroid
like betnovate can temporarily improve the appearance of the lesions but these usually tent to reappear once the steroid application is stopped....
Although very satisfactory treatment options are not available, but some amount of relief in itching and cosmetic improvement can be achieved with the various modalities available like
Topical steroids can be combined with salicylic acid
,Topical Tacrolimus,Topical calcipotriol
,Topical retinoic acid
derivatives or even oral drugs and chemical peels
in some cases...So i would advice you to see a skin specialist for confirmation of the diagnosis and proper managment..
Hope it helps
Dr Geetika Paul