Regarding pheochromocytoma, all of the following statements are correct EXCEPT:

Question

Accepted Answer

B. Clonidine suppression test is the first-line confirmatory test after elevated catecholamines are detected. ## Diagnostic Approach to Pheochromocytoma

### Screening and Confirmatory Tests

**Key Point:** Plasma free metanephrines (or 24-hour urine free metanephrines) are the **first-line screening tests** for pheochromocytoma, not clonidine suppression.

**High-Yield:** The clonidine suppression test is **NOT** a first-line confirmatory test. It is an **old test** rarely used in modern practice. The modern diagnostic algorithm is:

1. **Screen:** Plasma free metanephrines or 24-hour urine metanephrines (high sensitivity ~96–99%)
2. **Confirm:** If screening positive, perform **imaging** (CT/MRI abdomen) to localize the tumor
3. **Functional confirmation:** If imaging is equivocal, use **PET-CT** (e.g., ¹⁸F-DOPA PET) or **MIBG scintigraphy**, NOT clonidine suppression

**Clinical Pearl:** Clonidine suppression was historically used to distinguish pheochromocytoma from pseudopheochromocytoma (anxiety-induced catecholamine elevation), but this is rarely needed now given the high specificity of plasma metanephrines.

### Other Correct Statements

| Feature | Detail |
|---------|--------|
| **Plasma free metanephrines** | Superior sensitivity (96–99%) and specificity (85–89%) vs. 24-hour urine metanephrines; less affected by stress, posture, medications |
| **Rule of 10s (updated)** | Bilateral ~15%, Extra-adrenal ~15%, Malignant ~10–15%, Familial ~30–40% (higher than classic "10%") |
| **Hereditary associations** | MEN 2A/2B (RET), NF1, SDH (SDHA/B/C/D), VHL (~30–40% of all pheochromocytomas) |

**Mnemonic for Hereditary Pheochromocytoma — SDHMEN:** SDH mutations, Hereditary paraganglioma, MEN 2, Extra-adrenal tumors (paragangliomas), NF1

## Why This Question Tests High-Yield Knowledge

**Warning:** Clonidine suppression is a **classic exam trap**. Students often confuse it with the **phentolamine challenge test** (rarely done) or forget that it is **not first-line**. The modern standard is **plasma metanephrines → imaging → functional imaging if needed**.

[cite:Harrison 21e Ch 397]

Answer

A. The 'rule of 10s' (10% bilateral, 10% extra-adrenal, 10% malignant, 10% familial) is outdated; current data shows higher prevalence of these features

Answer

C. Approximately 30–40% of pheochromocytomas are associated with hereditary syndromes including MEN 2A/2B, NF1, SDH mutations, and VHL disease

Answer

D. Plasma free metanephrines have superior sensitivity and specificity compared to 24-hour urine metanephrines for diagnosis

Regarding pheochromocytoma, all of the following statements are correct EXCEPT:

Explanation

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