**Core Concept**
Peripheral neuropathy is a common complication in patients with diabetes mellitus, resulting from prolonged hyperglycemia and oxidative stress, leading to damage of the peripheral nerves.

**Why the Correct Answer is Right**
The peripheral nerves are composed of axons, myelin sheaths, and Schwann cells. Hyperglycemia in diabetes mellitus leads to activation of protein kinase C (PKC), increased production of advanced glycosylation end-products (AGEs), and activation of the polyol pathway, resulting in oxidative stress and accumulation of sorbitol. This oxidative stress causes damage to the myelin sheaths, axons, and Schwann cells, leading to pain, paraesthesia, motor weakness, and reflex loss.

**Why Each Wrong Option is Incorrect**
**Option A:** Leprosy is a chronic bacterial infection caused by Mycobacterium leprae, primarily affecting the skin, peripheral nerves, and mucous membranes. While leprosy can cause peripheral neuropathy, it is not the most common cause in diabetic patients.
**Option B:** Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis, primarily affecting the lungs, but can also affect other parts of the body, including the peripheral nerves. However, it is not commonly associated with the signs and symptoms described.
**Option C:** Rheumatoid arthritis is an autoimmune disease characterized by inflammation of the joints, but it can also cause peripheral neuropathy due to inflammation and damage to the nerves. However, it is not the most common cause of peripheral neuropathy in diabetic patients.

**Clinical Pearl / High-Yield Fact**
Peripheral neuropathy is a common complication of diabetes mellitus, affecting up to 50% of patients with diabetes. It is essential to screen diabetic patients for peripheral neuropathy and manage their blood glucose levels to prevent further nerve damage.

**Correct Answer:** C. Leprosy