MRCP2-3261
A 38-year-old woman has been diagnosed with relapsing remitting multiple sclerosis and is exploring further treatment options, including natalizumab. Despite receiving glatiramer acetate, she has experienced two severe relapses. Although she is still able to work, she feels fatigued and has limited mobility.
During her examination, the woman displays brisk reflexes bilaterally, with mild weakness in her proximal left leg and reduced sensation in her left foot. Her brain MRI reveals highly active disease with multiple acute and subacute plaques, as well as a single lower cervical cord lesion.
Before considering a new therapy, which investigation result is of the utmost importance, aside from HIV and general immunological status?