To date, all major guidelines designate LT4 as the standard. Are symptoms a reliable indicator of the presence of hypothyroidism? Fatigue in primary care, predicts a lifetime diagnosis of depression or anxiety more frequently than other outcomes. Tiredness has been examined in 26 meta-analyses. Only 4.3% of tired subjects have identifiable somatic disease (includes anemia, diabetes and hypothyroidism). In studies with control groups, the prevalence of somatic diseases was identical, an association that was clearly not causal. Based on symptoms, thyroid function testing occurs frequently but correlation with thyroid function is not significant. Symptoms or mild elevations in TSH result in labeling individuals as hypothyroid and the initiation of LT4. Reports show similar symptoms in euthyroid, subclinically hypothyroid (SCHypo) and overtly hypothyroid (OHypo) patients, overlap between the groups is clear. Others reinforce the non-specificity of symptoms especially among older women. Do circulating T3 levels correlate with symptoms of hypothyroidism or predict response to LT4/LT3? Several studies demonstrate no correlation between serum T3 (on LT4) and QOL and mood. Massolt et al. demonstrated no correlation of QOL with serum T3 levels but recognized positive factors such as the time since the diagnosis of the thyroid cancer and a negative correlation with the number of all drugs ingested by the subjects. Two studies showed that T3 levels measured while on LT4 or after treatment with LT4/LT3 did not predict a positive response to LT4/LT3. Two patient surveys, shed light on patient satisfaction. The most satisfied patients are followed by primary care physicians, ingest thyroid hormone extract (DTE), have lower TSH values and adjust their doses based on symptoms. The second study reported equivalent overall satisfaction on LT4 or LT4/LT3 while DTE was superior. Dissatisfaction with weight, fatigue, mood, and memory were similar in those on LT4 and those on LT4/LT3 while DTE users complained less. Symptoms are imprecise. Utilizing T3 levels to make clinical decisions and/or predict the outcome of LT4/LT3 is not substantiated. Pending further research in new areas like DIO2 SNPs and LT4/LT3 sustained release, I will continue to utilize levothyroxine monotherapy.
18 - 21 May 2019
European Society of Endocrinology