My family is a member of the IDF (Immune Deficiency Foundation) community. This sounds like a type of immune deficiency I heard about at a the Phoenix convention. Can't remember the name now, but if that is the only symptom it is rare. They showed pictures of people who had swollen up in only one hand, shoulder or arm. If I remember it was a type of a "complement deficiency"
The IDF website is www.primaryimmune.org give them a call, they have lists of immunologists in your area and maybe that is a place to start.
Hope this is helpful.