Thanks for writing here.
Elevated IgM and ra factor suggest some auto immune disease.Biopsy
report will find out exact diagnosis.
Increasing the dose of prednisolone
like 40 or 60 mg will help to reduce itching.
Sedative antihistaminc like atarax 25 mg will help.
At times dapsone
is a very good drug for auto immune disorders
You need to consult your doctor before taking any medicines.
Hope this will help you.Take care.