A 52-year-old woman with primary hypothyroidism on levothyroxine replacement presents with persistent fatigue and weight gain despite TSH normalization. Which of the following is NOT a recognized cause of persistent symptoms in adequately treated hypothyroidism?

Question

Accepted Answer

A. Excessive TSH suppression leading to iatrogenic thyrotoxicosis. ## Persistent Symptoms Despite TSH Normalization

This question addresses a common clinical scenario: patients with hypothyroidism who remain symptomatic even when TSH is normalized on levothyroxine therapy.

### Recognized Causes of Persistent Symptoms

**Key Point:** The following are well-established reasons for ongoing symptoms despite normalized TSH:

1. **Inadequate T4→T3 conversion** — Selenium and iron deficiency impair deiodinase enzymes, reducing bioavailable T3 [cite:Harrison 21e Ch 376]
2. **Malabsorption disorders** — Celiac disease, pernicious anemia, and inflammatory bowel disease reduce levothyroxine absorption
3. **Non-adherence** — Erratic dosing or poor compliance is a common cause
4. **Comorbid conditions** — Depression, fibromyalgia, sleep apnea, and other chronic illnesses may coexist

### Why Excessive TSH Suppression Is NOT the Answer

**High-Yield:** Excessive TSH suppression (TSH <0.1 mIU/L) causes **iatrogenic thyrotoxicosis**, which manifests as:
- Tachycardia, palpitations, tremor
- Weight loss (not weight gain)
- Heat intolerance
- Anxiety

The patient in this stem has **fatigue and weight gain** — the opposite of thyrotoxic symptoms. Over-replacement would not explain her presentation. In fact, over-suppressed TSH would be immediately apparent on laboratory testing and would require dose reduction, not investigation of other causes.

**Clinical Pearl:** TSH normalization with persistent symptoms should prompt investigation of malabsorption, nutritional deficiencies (selenium, iron, B12), and comorbid psychiatric or rheumatologic conditions — not reassessment of the TSH target itself.

### Summary Table

| Cause | Mechanism | Clinical Clue |
| --- | --- | --- |
| Selenium deficiency | ↓ Deiodinase activity | Low T3 syndrome |
| Celiac disease | Malabsorption | Diarrhea, weight loss, anemia |
| Non-adherence | Subtherapeutic levels | Inconsistent dosing history |
| Over-replacement | Excess T4/T3 | Tachycardia, weight loss, low TSH |

Answer

B. Inadequate peripheral conversion of T4 to T3 due to selenium deficiency

Answer

C. Concurrent celiac disease causing malabsorption of levothyroxine

Answer

D. Non-adherence to levothyroxine dosing schedule

A 52-year-old woman with primary hypothyroidism on levothyroxine replacement presents with persistent fatigue and weight gain despite TSH normalization. Which of the following is NOT a recognized cause of persistent symptoms in adequately treated hypothyroidism?

Explanation

Practice similar questions