What specialty manages euthyroid sick syndrome (ESS)?

Management of Euthyroid Sick Syndrome

Primary Specialty Responsible for Management

Euthyroid sick syndrome (ESS), also known as non-thyroidal illness syndrome, is primarily managed by the specialty treating the underlying critical illness—most commonly internal medicine, critical care medicine, or the relevant subspecialty (cardiology, pulmonology, nephrology) managing the acute systemic disease. Endocrinology consultation may be sought for complex cases requiring differential diagnosis from true thyroid disease, but ESS itself does not require routine endocrinology management 1, 2.

Clinical Context and Rationale

Understanding ESS as a Secondary Phenomenon

• ESS represents abnormal thyroid function tests occurring in patients with acute or chronic systemic illnesses who do not have intrinsic thyroid disease 1, 2, 3.
• The syndrome is characterized by low serum T3, elevated reverse T3 (rT3), normal or low T4, and normal or inappropriately low TSH levels 1, 2.
• ESS is believed to be an adaptive physiological response to severe illness aimed at reducing metabolic rate and conserving energy during physiological stress 2, 3.

Disease Settings Where ESS Commonly Occurs

• ESS is most frequently observed in critically ill patients with conditions including: chronic obstructive pulmonary disease with acute respiratory failure, diabetic ketoacidosis, heart failure, chronic kidney disease, severe sepsis, neoplasms, ischemic heart disease, acute cerebral vascular events, liver diseases, and chronic renal failure 4, 3.
• The incidence of ESS in hospitalized internal medicine patients is approximately 23%, making it significantly more common than primary thyroid disease (5%) 4.
• The degree of thyroid function impairment correlates directly with disease severity, and low thyroid hormone levels (particularly T4) predict poor prognosis 1.

Specialty Assignment Algorithm

Primary Management Responsibility

• The treating physician managing the underlying acute or chronic systemic illness maintains primary responsibility for ESS 1, 4, 2.
• For heart failure patients: cardiology manages both the cardiac condition and associated ESS 3.
• For critically ill ICU patients: critical care/intensive care medicine manages ESS 1, 2.
• For patients with diabetic ketoacidosis: endocrinology or internal medicine manages the metabolic crisis and associated ESS 4.

When to Involve Endocrinology

• Endocrinology consultation is appropriate when: differential diagnosis between ESS and true thyroid disease (hypothyroidism, hyperthyroidism, or subclinical thyroid dysfunction) is uncertain, particularly when no pre-illness thyroid function tests are available for comparison 1.
• Endocrinology should be consulted if: the patient has a known history of thyroid disease requiring clarification of whether current abnormalities represent ESS superimposed on thyroid pathology 1.
• Endocrinology involvement may be considered for: complex cases where thyroid hormone replacement therapy is being contemplated, though current evidence does not support routine treatment of ESS 2.

Critical Diagnostic Pitfalls to Avoid

Distinguishing ESS from True Thyroid Disease

• Interpretation of thyroid function tests in critically ill patients is challenging and requires understanding that ESS mimics thyroid dysfunction without representing true thyroid pathology 1.
• The key distinguishing feature is clinical context: ESS occurs in the setting of severe systemic illness, whereas primary thyroid disease typically presents with thyroid-specific symptoms and signs 1, 2.
• In ESS type I (most common, 63% of cases): T3 is low with elevated rT3 due to reduced 5-deiodinase enzyme activity 4.
• In ESS type III (30.5% of cases): T4 is elevated due to increased thyroid-binding globulin (TBG), resulting in reduced peripheral hormone activity 4.

Avoiding Inappropriate Treatment

• Treatment of ESS with thyroid hormone replacement to restore normal serum levels does not provide clear benefit and is not currently recommended 2.
• The controversy exists whether the fall in thyroid hormones is adaptive (normal physiologic response) or maladaptive (requiring treatment), but available data do not support routine thyroid hormone supplementation 1, 2.
• Focus should remain on treating the underlying systemic illness, as resolution of ESS typically occurs with recovery from the primary disease 1, 2.

Monitoring and Prognostic Implications

• Serial thyroid function testing during critical illness should be interpreted cautiously, recognizing that worsening thyroid parameters reflect disease severity rather than thyroid pathology 1.
• In chronic heart failure patients, 44.29% exhibit low T3 levels, with negative correlation between NT-proBNP levels, Boston score, and total T3, indicating that thyroid suppression increases with heart failure severity 3.
• Routine thyroid function assessment in heart failure patients can guide intensive monitoring and optimized heart failure management rather than thyroid-specific interventions 3.