Over months, the numbness has become more pronounced and involves a dense area bilaterally from the sternal notch to the area behind the ear. On examination, scalp sensation, cranial nerve function, and upper extremity motor examination are normal. The patient has decreased pain and temperature sensation in the distribution of C4. Vibration sense is normal. Cranial and caudal to the affected area, sensation is intact. Bladder and anal sphincter function are also normal. What is the most likely cause of this patient’s neurologic disorder?
A.blood lead level
B. fasting blood glucose
D.rapid plasma reagin for syphilis
E. red blood cell folate levels