Hi, dear I have gone through your question. I can understand your concern. First of all he should investigate properly. Whether he has multiple myeloma or not. He should go for protein electrophoresis and bone marrow examination. It will give you exact diagnosis. Mediastinal lymphadenopathy may be due to metastatic lesion or some other cause. You should go for excision biopsy and take treatment according to cause. Consult your doctor and take treatment accordingly. Hope I have answered your question, if you have doubt then I will be happy to answer. Thanks for using health care magic. Wish you a very good health.