A 63-year-old man develops edema, and dyspnea on exertion. He has no prior cardiac or renal conditions, and his examination is significant for macroglossia, elevated jugular venous pressure (JVP), hepatomegaly, and 3+ pedal edema. His investigations reveal 3.5 g/d of protein in the urine, anemia, normal fasting glucose, and serum immunoelectrophoresis is positive for a monoclonal immunoglobulin. Which of the following is the most characteristic neurologic finding associated with this condition?