Thickening and darkening of knuckles could be due to acanthosis nigricans
, frictional injury, eczema
The treatment suggested by your doctor is apt and will definitely give you results. Emollients reduce dryness, make skin soft while steroid
and salicylic acid
will reduce pigmentation and thickening of skin. However it would be difficult to predict the time required to get desirable results.
Hope that answers your query.