Polyneuropathy inflammatory or toxic?

A 68-year-old man experienced 'prickling' and 'burning' in his toes; the sensations spread up his legs, after affecting his hands and then his chest. These symptoms worsened over six months, then slowly improved over the next three months. Unsteadiness in walking was also reported. Cranial nerve function and muscle strength were normal except for weight bearing when he walked on his heels. Tendon reflexes were normal in the arms and absent in the legs. The toes turned down on plantar stimulation. Perception and touch-pressure, pinprick, joint position, and vibration was abnormal in the feet. The nerve conduction velocity of motor (elbow to wrist) and sensory (finger to above wrist) fibers of median and ulnar nerves was slightly abnormal. Peroneal and sural nerve conduction could not be measured because of absence of any response. Needle electromyography revealed denervation in distal muscles. A twofold increase in urinary mercury and an elevation in cerebrospinal fluid protein had been discovered before referral. The patient was unaware of any exposure to mercury. He ate red snapper about once every 10 days.