Kathy, I also am diagnosed with MS. I don't know if there is a correlation, tho, to costochondritis. I also had an auto accident as I said in above post and my ribs and rib/sternum and mid-back have been only getting worse ever since.
There are no tests for it other than a good exam and history. They know by description and where the pain is and that hard lump you described. I have to tell you I didn't think it would ever be less painful again, until I changed PT clinics. My dr. sent me for myofascial pain release massage, stretch and deep tissue work along with the ultrasound put on the sternum and lump and on the back,(wraps around with the ribs to the mid-back).Then, they do massage therapy afterwards and I do stretches at home given me for rib expansion and breathing.
Had another PT appt. today and I could report when they ask "how are you doing", better! Never thought I'd be saying that. It is like a house of horror to live with costochondritis. You can't think of anything except how much it hurts and not breathing right. I am getting better. Then, I went to the chiro who adjusts the ribs.(not every time!) A couple get put back in and it is painful and then you gradually get better with the combined treatments. I hope this helps you, be sure to buy MSM supplement and I do take pain medication and muscle relaxant. I am not on ABC drugs for MS, but a natural approach to MS with diet. Soleil