What Causes Numbness And Weakness In Lower Legs?

i have been diagnosed with MGUS. at last count my igm was lower (389)than the first time (550). the problem is last summer I felt like I has some sort of attack with pins and needles throughout my body, "zapping" sensations, and feelings of numbness as well as weakness in my lower legs. To date it is a year later, and although the sensations are nowhere as intense, they still remain . My hematologist wants to do a cat scan of the chest and pelvis to look for enlarged lymph nodes. Could you explain what exactly hes looking for? Ive read that some people with high IGM also can have some neuropathy