**Core Concept**
Prolonged treatment with Isoniazid (INH) can lead to a deficiency of a crucial enzyme involved in the metabolism of amino acids. This deficiency can cause a range of clinical symptoms, particularly affecting the nervous system.

**Why the Correct Answer is Right**
Isoniazid is known to inhibit the enzyme pyridoxine (vitamin B6) kinase, which is necessary for the activation of pyridoxine. Prolonged treatment with INH can lead to a deficiency of pyridoxal phosphate, the active form of vitamin B6. This deficiency can cause a range of symptoms, including peripheral neuropathy, seizures, and cognitive impairment. The mechanism underlying this deficiency involves the inhibition of pyridoxine kinase, which is necessary for the conversion of pyridoxine to pyridoxal phosphate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because INH treatment does not directly lead to a deficiency of folate, which is another essential vitamin involved in amino acid metabolism.

**Option B:** This option is incorrect because INH treatment does not directly lead to a deficiency of thiamine (vitamin B1), which is involved in carbohydrate metabolism.

**Option C:** This option is incorrect because INH treatment does not directly lead to a deficiency of riboflavin (vitamin B2), which is involved in energy metabolism.

**Clinical Pearl / High-Yield Fact**
It is essential to supplement patients with INH with pyridoxine (vitamin B6) to prevent deficiency and associated clinical symptoms. This is particularly important in patients with malnutrition, alcoholism, or other conditions that may increase the risk of pyridoxine deficiency.

**Correct Answer:** B. Pyridoxine.