What is the appropriate work‑up to diagnose Multiple Endocrine Neoplasia type 2 (MEN 2)?

MEN 2 Diagnosis

The diagnosis of MEN 2 is established through germline RET proto-oncogene genetic testing, which should be performed in any patient with medullary thyroid carcinoma (MTC), pheochromocytoma with family history, or clinical features suggestive of MEN 2A or 2B, followed by biochemical screening with serum calcitonin, plasma/urine metanephrines, and serum calcium to identify disease manifestations 1.

Diagnostic Algorithm

Step 1: Identify Candidates for Genetic Testing

Clinical indications for RET genetic testing include:

• Any patient diagnosed with MTC (sporadic or familial)
• Pheochromocytoma with family history or bilateral presentation
• Primary hyperparathyroidism with MTC or pheochromocytoma
• First-degree relatives of confirmed MEN 2 patients
• Clinical features of MEN 2B: mucosal neuromas, intestinal ganglioneuromatosis, marfanoid habitus, alacrima, or constipation 1

Critical pitfall: Approximately 50% of MEN 2B cases occur de novo, so absence of family history does not exclude the diagnosis. The presence of mucosal neuromas, alacrima, or characteristic physical features should immediately trigger RET testing 1.

Step 2: Perform RET Genetic Testing

Comprehensive RET gene sequencing should target exons 5,8,10,11,13,14,15, and 16, with exons 10 and 11 comprising 95% of MEN 2A mutations 1, 2. The most common mutations include:

• MEN 2A: Codon 634 variants (most common), codon 618 variants
• MEN 2B: p.M918T (majority of cases), rarely p.A883F
• Familial MTC: Various moderate-risk RET variants 1, 3

The RET mutation determines the American Thyroid Association (ATA) risk classification (Highest, High, or Moderate), which dictates timing of surveillance and prophylactic surgery 1.

Step 3: Biochemical Screening

Once a RET mutation is confirmed, or in patients with high clinical suspicion pending genetic results, perform the following:

For MTC detection:

• Serum calcitonin (most sensitive marker for MTC)
• Calcitonin levels approaching or exceeding 20 pg/mL indicate need for thyroidectomy, as lymph node metastases are rarely observed below this threshold 4
• Important caveat: Calcitonin levels before age 3-5 years may be physiologically elevated; use age-specific reference ranges to avoid false positives 4

For pheochromocytoma detection:

• Plasma or 24-hour urine metanephrines (fractionated)
• Screen annually starting at age 16 years in confirmed RET carriers 4
• Pheochromocytoma can occur as early as age 8 years, though typically presents in the 4th-5th decade 1

For primary hyperparathyroidism (MEN 2A only):

• Serum calcium (corrected for albumin)
• Screen annually starting at age 16 years 4
• Note: PHPT does not occur in MEN 2B (particularly M918T carriers) 1

Step 4: Imaging Studies

Thyroid ultrasound is NOT recommended for routine surveillance, as calcitonin is more sensitive for detecting early MTC 4. However, ultrasound should be performed when:

• Calcitonin is elevated or increasing (for surgical planning and lymph node assessment)
• Post-operatively only if calcitonin levels are rising 4

Adrenal imaging (CT or MRI) should be performed when biochemical screening suggests pheochromocytoma.

Genotype-Phenotype Correlations

Understanding the specific RET mutation provides critical prognostic information:

• ATA-Highest risk (e.g., M918T): >95% lifetime MTC risk, earliest onset (infancy in MEN 2B), 50% pheochromocytoma risk 1
• ATA-High risk (e.g., codon 634): >95% MTC risk, 50% pheochromocytoma risk, 20-30% PHPT risk 1
• ATA-Moderate risk: 10-50% pheochromocytoma risk (variant-dependent), later MTC onset 1

Codon 634 variants are specifically associated with higher risks of both pheochromocytoma and PHPT, as well as cutaneous lichen amyloidosis 1.

Cascade Testing

Once a proband is identified, offer genetic testing to all first-degree relatives using familial mutation testing (testing for the specific known variant) 1.

Timing of genetic testing in at-risk children:

• ATA-Highest or High risk families: Test as soon as risk is known to facilitate early surveillance and management 4
• ATA-Moderate risk families: May defer testing until age 5 years when surveillance begins, though this must be balanced against risk of loss to follow-up 4

Genetic counseling is essential to help families understand variable penetrance, particularly for moderate-risk variants where disease manifestations are highly variable 4.

Key Clinical Distinctions

MEN 2A vs MEN 2B:

• MEN 2A: MTC + pheochromocytoma + PHPT (classical), may have cutaneous lichen amyloidosis or Hirschsprung disease
• MEN 2B: MTC (earlier, more aggressive) + pheochromocytoma + mucosal neuromas + ganglioneuromatosis, NO PHPT 1

Prevalence: MEN 2A accounts for 91% of MEN 2 cases (35% isolated familial MTC), MEN 2B represents 9% 1.