4 months is a long time to have any particular rash
Dermatology is a very 'visual' field & as such, this rash needs to be viewed & it would be great if you could upload a clear digital photograph of the lesion onto this website using the upload data icon.
Alternatively, do visit a second dermatologist
for best results as you seem to have done a skin biopsy
as well..What were the results of the biopsy?
One should test for allergens butthat is only possible 2 weeks after complete stoppage of the corticosteroids
Elevated platelets need not be significant but a host of other tests are required & you need to be seen in person am afraid.
Cheers & wish you a speedy recovery.
Dr Praveen Rodrigues MD
Dermatologist, Cosmetologist, Venereologist
Vikram Hospital, Bangalore, India.