Unilateral hand swelling without other symptoms could be any number of things. The most classic presentation would be a woman who had a left-sided radical masectomy a few years ago who is now presenting with unilateral lymphedema in her left hand. However, since you say that she has no PMHx, it sounds like that's not likely. Other possibilities include anything could by causing some type of lymph-obstruction, eg infectious vs metastatic vs genetic etiologies. Infectious possibilites include parasites, specifically nematodes or worms. Generally not common in the US, but it should be considered if there is a travel history to somewhere like Africa or central or south America. Metastatic possibilities include something like a lymphoma causing lymph obstruction, or even breast cancer that has metastasized causing lymphatic obstruction in the axillary lymph nodes. Genetic etiologies seem unlikely given her age (most present at a younger age), but I wouldn't rule them out if we can't find any other etiology. If it's not lymphedema, it could be something like hand cellulitis or maybe a DVT causing venous insufficiency of her L extremitity. Anyways, it's very difficult to really say what the most likely etiology is without doing a physical exam and seeing what your friend is calling "hand swelling". If she hasn't already, I'd definitely reccomend that your friend see a physician. If she has already, and her physician is stuck, she might reccomend that he or she order a right upper extremity ultrasound to look for DVT's and possibly a CT with contrast to see some of the anatomy there. Let us know what it turns out to be.
