Andy, some diagnostic tools they can use, in order of less expensive to more expensive, would be feeling around/visual, ultrasound, apparantly a good ultrasound technologist can tell a lot. Needle biopsy, which is the most definiative way of telling what's going on. and PET/CT, scan.

Step after that which is more invasive is to remove one of the swollen nodes and do a biopsy.

There's probably other trics and things they can do, I'm not a medica professional but all of the above have been done on me.

Bob