A 60 year old man presents with numbness of both feet for 2 months. He was diagnosed with type 2 diabetes mellitus 6 years ago, which is well controlled on Metformin alone. His medical history is otherwise unremarkable. He consumes a mixed diet and only drinks socially. His HbA1c is 6.0%, while a recent full blood count and serum creatinine were normal.
There is a length dependent sensory and motor polyneuropathy.
ESR: 10 mm/1h The serum plasma electrophoresis shows a normal pattern.
Serum Vitamin B12: 95 pg/ml (200 - 900) Serum Folate: 10 ng/ml (5 - 16)
Serum TSH: 1.0 mIU/L (0.4 - 4)