What should be monitored and considered from an endocrinology perspective in patients with Pendred syndrome?

Endocrine Monitoring in Pendred Syndrome

From an endocrinology standpoint, you must monitor thyroid function longitudinally with TSH, free T4, and thyroid ultrasound, as hypothyroidism can develop or recur unpredictably even after initial euthyroid periods, and these patients require lifelong surveillance for goiter development and thyroid nodules with a low threshold for fine-needle aspiration given emerging evidence of increased thyroid malignancy risk.

Thyroid Function Monitoring

Initial and Ongoing Assessment

• TSH and free T4 measurements are essential at diagnosis and should be repeated regularly throughout life 1
• Hypothyroidism may present in several patterns:
  • Present at birth (detectable by neonatal screening)
  • Initially abnormal but spontaneously normalizing, then recurring later 1
  • Developing de novo in childhood or adulthood
• Critical pitfall: Two children in the Victorian screening program were nearly misdiagnosed as having "transient hypothyroidism" when their initial abnormalities normalized, only to become hypothyroid again later 1

Thyroid Status Variability

The thyroid phenotype in Pendred syndrome is highly variable 2, 3, 4:

• Only 80% of genetically confirmed patients develop thyroid impairment 3
• Patients may be euthyroid or hypothyroid
• Thyroid dysfunction is modified by dietary iodine intake 4
• Goiter is rarely present at birth but develops over time 3

Goiter and Nodule Surveillance

Structural Monitoring

• Thyroid ultrasound should be performed regularly to assess:
  • Goiter development (present in classic triad but timing varies)
  • Nodular disease (universal finding in surgical series) 5
  • Nodule characteristics requiring further evaluation

Thyroid Malignancy Risk

Emerging evidence suggests thyroid cancer occurs in approximately 1% of Pendred syndrome patients 6, which is higher than background population risk:

• Follicular thyroid carcinoma is the reported histologic type 6, 7
• One case series emphasized "high risk of malignancy" in thyroid nodules 7
• Histopathological studies show follicular nodular disease and follicular adenomas are common 5

FNA Indications (Apply Standard Guidelines with Lower Threshold)

Following AACE/ACE guidelines 8, but with heightened vigilance:

• Nodules >10 mm without definite benign appearance warrant FNA
• Nodules 5-10 mm with suspicious ultrasound features should undergo FNA
• Nodules ≥20 mm even if predominantly cystic or spongiform
• Consider FNA at smaller sizes given the documented malignancy association

Perchlorate Discharge Test

• Historically used to confirm impaired iodide organification 2
• Positive test is characteristic but not required for diagnosis in the genetic era
• May help distinguish from other causes of dyshormonogenesis when genetic testing is unavailable

Levothyroxine Management

• Initiate levothyroxine when hypothyroidism develops (TSH elevated, low free T4)
• Do NOT use suppressive LT4 therapy in euthyroid patients with goiter 8
• Monitor for recurrence of hypothyroidism even if initially euthyroid or after spontaneous normalization 1

Genetic Confirmation

• Sequence all 21 exons of SLC26A4/PDS gene when clinical diagnosis is suspected 3
• Genetic testing is essential because phenocopies are common—in one series, 5 of 9 clinically diagnosed patients had no PDS mutations 3
• Once pathogenic variants identified, family-based screening is recommended 6

Coordination with Other Specialists

While not purely endocrine, be aware:

• Audiometry: Hearing loss may be progressive, requiring repeated assessments 1
• Inner ear imaging: Enlarged vestibular aqueduct and Mondini malformations are hallmarks 2
• The hearing impairment is the primary morbidity driver, not the thyroid disease

Surveillance Schedule

A practical approach:

• At diagnosis: TSH, free T4, thyroid ultrasound, genetic testing
• First 5 years: TSH/free T4 every 6-12 months, ultrasound annually
• Lifelong: Annual TSH/free T4, ultrasound every 1-2 years
• Any nodule detected: Apply standard FNA criteria but with lower threshold given malignancy reports 6, 7

Key Pitfall to Avoid

Never assume thyroid function will remain stable—the Victorian experience demonstrates that initial normalization does not predict long-term euthyroidism, and discontinuing monitoring after apparent resolution can result in missed hypothyroidism 1.