The causes are different for different types of diabetic neuropathy. Nerve damage is likely due to combination of factors:-
METABOLIC factors as high blood pressure, long duration of diabetes, abnormal blood fat levels and possible low levels of insulin.
NEUROVASCULAR factors leading to damage to blood vessels that carry oxygen and nutrients to nerves.
INFLAMMATION in nerves.
INJURY to nerves.
INHERITED traits that increase susceptibility to nerve disease.
LIFE STYLE factors such as smoking and/ or alcohol use.