Endocrine Abstracts

Background: Desiccated thyroid extract (DTE) is derived from the porcine thyroid gland, which has a higher triiodothyronine content than the human thyroid gland. DTE was standard therapy for hypothyroidism until the mid-1970s and is still in use, even though it is not recommended in current guidelines. This review aimed to summarize the available literature on DTE treatment in adult hypothyroid patients.

Methods: The search was conducted in six electronic databases until January 6, 2024. Two reviewers independently screened all search results. The retrieved studies compared DTE treatment with levothyroxine or combination therapy with liothyronine and levothyroxine. The primary outcome was quality of life (QoL), and secondary outcomes included symptoms, treatment preference, adverse effects, thyroid function measures, thyroid autoantibodies, body weight, cardiovascular measures, and gene polymorphisms in the deiodinase enzymes. One author performed data extraction twice. Risk of bias for each study was conducted by two authors independently. The risk of bias in non-randomized studies of intervention (NRSIs) was judged with ROBINS-I, and for randomized clinical trials (RCTs), ROB 2.0 was used. The overall quality of evidence was judged with GRADE.

Results: In the qualitative synthesis, we included nine NRSIs, two RCTs, and three case reports. The overall quality of evidence for the various outcomes was moderate to very low. The RCTs found no difference between treatments regarding QoL and symptom score assessments. In the NRSIs, symptom and QoL assessments were in favor of DTE. The included studies indicated that DTE may cause an increase in heart rate, lower body weight, and lower high-density lipoprotein compared to other treatment regimens, but the results were conflicting. The included NRSIs were judged with moderate to critical risk of bias. The RCTs had some concerns as no a priori statistical analysis plan was available. The overall quality of evidence for QoL was rated as low.

Conclusions: Most studies of DTE treatment are hampered by an inferior design, and data on long-term effects and side effects are lacking. Further, the various methods used for evaluating QoL and symptom scores complicate comparison across studies. The two included RCTs could not demonstrate any difference in QoL or symptom scores when comparing DTE with other thyroid hormone substitutions. Future trials of DTE in patients with hypothyroidism should be based on adequate study designs, validated measures of QoL, patients with reduced QoL, and the assessment of biomarkers reflecting long-term adverse effects.