Endocrine Abstracts

JOINT847

Introduction: Hypothyroidism is a chronic disease with a high prevalence. The treatment of choice in most patients is synthetic levothyroxine (LT4) adjusted for body weight. The objective is to achieve normal levels of thyrotropin (TSH) (0.4-4 µU/ml). Refractory hypothyroidism is defined as persistent hyperthyrotropinemia despite high doses of LT4. Once the usual causes (pharmacological, dietary and/or pathological) that would justify LT4 malabsorption have been ruled out, as well as possible interferences in the measurement of TSH, a dynamic LT4 absorption test (DAT) can be performed. The test allows us to differentiate real malabsorption from pseudomalabsorption or lack of therapeutic adherence. Our purpose is to demonstrate the importance of using DAT in clinical practice.

Case Report: 60-year-old woman, under study for difficult-to-control autoimmune primary hypothyroidism (APH), on treatment with Levothyroxine. TSH levels of 166 µU/ml (0.270-4.200) and FT4 of 0.34 ng/dl (0.930-1.700) with significant weight gain (>10 kg), BMI 32.95 (Obesity-Grade-I). Her Primary Care Physician (PCP) increased the dose of Levothyroxine. After a new analytical control, the following were observed: TSH 273.00 µU/ml, FT4 0.221 ng/dl, FT3 1.380 pg/ml (2.00-4.40) and IgG-antiperoxidase-TPO Ac. 187.00 IU/ml (9.00-34.00). The patient began with significant asthenia, hoarseness and dyspnea. Complementary tests were performed to assess intestinal and autoimmune causes, which were negative. There was no analytical interference (macro-TSH and heterophil antibodies). Subsequently, TSH levels were 243.00 µU/ml and FT4 0.308 ng/dl. DAT was performed, which consisted of the administration of 1000 µg of FT4 and monitoring of FT4 levels every 30 min for 4 hours. A baseline ECG and a blood test with TSH and FT4 must be performed beforehand. Absorption is considered normal when FT4 levels are >0.4 ng/dl with respect to the baseline value (absorption >60%). Results: DAT results: 0’ TSH 207.00 and FT4 0.277; 30´ FT4 0.293; 60´ FT4: 0.550; 90´ FT4 0.862; 120´ FT4 1.63. 180´ FT4 1.950; 240´ TSH 70.90 and FT4 2.00, in µU/ml and nd/dl, respectively.

Discussion and conclusions: According to the results, everything indicates a pseudomalabsorption of FT4, that is, a lack of therapeutic compliance by the patient. Correct adherence to treatment is insisted upon. After 8 weeks, the thyroid profile is shown to be normalized (TSH 1.080 µU/ml, FT4 1.50 ng/dl, FT3 3.090 pg/ml). DAT is a safe and effective method that allows pseudomalabsorption to be demonstrated after ruling out interferences and underlying gastrointestinal pathology. pseudomalabsorción tras descartar interferencias y patología gastrointestinal subyacente.