**Question:** A 72-year-old man is brought to the clinic by his daughter because she is concerned about his memory. A careful history, mini mental status, and physical examination confirm your suspicions of the patient having Alzheimer disease. Which of the following investigations is included in the initial work-up for reversible causes of dementia?

A. Complete blood count (CBC)
B. Electroencephalogram (EEG)
C. Vitamin B12 and folate levels
D. Thyroid function tests

**Core Concept:**

Reversible causes of dementia are conditions that can potentially be treated or managed to improve cognitive function. Alzheimer's disease is typically irreversible, but some reversible causes need to be considered before diagnosing Alzheimer's disease.

**Why the Correct Answer is Right:**

C. Vitamin B12 and folate levels are essential investigations to rule out nutritional deficiencies that can cause dementia. Vitamin B12 and folate deficiencies can lead to a condition called pernicious anemia, which can cause cognitive decline and dementia-like symptoms.

**Why Each Wrong Option is Incorrect:**

A. A complete blood count (CBC) is primarily used to evaluate the patient's overall hematological status and rule out anemia. CBC is not specifically targeted for dementia workup.

B. Electroencephalogram (EEG) is used to evaluate the electrical activity of the brain, primarily for epilepsy diagnosis and monitoring. It is not a standard test for dementia evaluation and does not help in identifying reversible causes.

D. Thyroid function tests (TFTs) are used to assess thyroid hormone levels, primarily for hypothyroidism evaluation. Hypothyroidism can cause cognitive symptoms, but TFTs are not specifically designed for dementia work-up, and considering Alzheimer's disease in the primary differential diagnosis is more relevant in this context.

**Clinical Pearls:**

Investigating reversible causes of dementia is crucial to ensure an accurate diagnosis and better management of the patient. Although some investigations like TFTs are essential in general patient evaluation, considering Alzheimer's disease as the primary differential diagnosis allows focusing on more targeted investigations like vitamin B12 and folate levels.

**Correct Answer Explanation:**

The correct answer, vitamin B12 and folate levels, is vital as deficiencies in these vitamins can lead to dementia-like symptoms in patients. By excluding these potential causes, the remaining differential diagnoses become more focused on Alzheimer's disease, which is a primary consideration in dementia workup.

**Why Each Wrong Option is Incorrect:**

Option A (CBC) is incorrect as it is primarily used for hematological evaluation and not relevant for dementia workup. Option B (EEG) is not specifically designed for dementia evaluation and does not aid in identifying reversible causes. Option D (TFTs) is essential in general patient evaluation, but excluding specific dementia-related causes like vitamin B12 and folate deficiencies is crucial.