Falling eyebrows: alopecia or not? I have been losing my eyebrows now for 4 years.

You'll want to see a dermatologist who can understand your history and carefully examine the eyebrows.  Causes of brow loss include alopecia areata, frontal fibrosing alopecia, thyroid disorders, metabolic disorders, trichtoillomania, telogen effluvium, age related changes over-tweezing.  Itchy eyebrows are quite different in causation and can include some of the above but may include seborrheic dermatitis, and other inflammatory conditions.  

There are diseases that cause the eyebrows to lose hair.  See a dermatologist who has the experience as the diagnosis can often be made on an office examination