A 50-year-old sailor presents with recent weight loss of 2 kg. Upon further inquiry, he reports experiencing painful sensations in his legs at night, reduced sensation in his feet, and some issues with balanitis and urinary frequency. During the examination, he exhibits diminished proprioception at the toes, absent ankle reflexes, and a small painless ulceration on the ventral aspect of the big toe. His BMI is 28 kg/m2. Nerve conduction studies reveal reduced motor conduction velocities (75% of normal) in the legs, with small, poorly formed sensory nerve action potentials. Electromyography shows evidence of active denervation in the lower limbs with positive sharp waves and fibrillations. What is the most probable diagnosis?