Pseudo-Malabsorption in High Dose Levothyroxine-Resistant Hypothyroidism

Area of Science:

• Endocrinology
• Internal Medicine

Background:

• Levothyroxine (LT4) is the standard treatment for hypothyroidism.
• Persistent subclinical or overt hypothyroidism despite adequate LT4 dosing can occur.
• Differential diagnosis includes malabsorption and nonadherence.

Observation:

• A patient with hypothyroidism presented with persistently abnormal thyroid function tests despite escalating LT4 and liothyronine doses.
• Initial investigations for malabsorption were negative.
• An oral LT4 loading test suggested pseudo-malabsorption, prompting patient disclosure of nonadherence.

Findings:

• The LT4 loading test revealed adequate absorption, contradicting initial assumptions of malabsorption.
• Patient-reported adherence was inaccurate; nonadherence was the primary cause of treatment resistance.
• Multidisciplinary intervention and simplified treatment led to normalized thyroid function.

Implications:

• Thorough patient history and medication adherence assessment are critical in managing treatment-resistant hypothyroidism.
• Nonadherence should be suspected and investigated when thyroid function remains suboptimal despite high LT4 doses.
• Targeted interventions, including counseling and treatment simplification, can effectively resolve nonadherence-related hypothyroidism.