A 67-year old-woman presents to the clinic for evaluation of numbness in her feet. The symptoms started gradually and are more noticeable now. There is no weakness in her feet or difficulty walking. Her past medical history is significant for Type 2 diabetes for the past 10 years and she currently takes metformin and glyburide. Physical examination confirms sensory loss in the feet to touch and vibration. Which of the following is most characteristic of diabetic neuropathy?