Commentary | Aug 23, 2015 Recommendations: +1

Substitution therapy with levothyroxine is easy in 90% of persons affected from hypothyroidism. 10%, however, suffer from so-called syndrome T, i.e. poor quality of life despite normal TSH levels. Results of a recent study could explain, why dosage requirements are different in some patients.

Recently, results of a trial with 353 hypothyroid subjects on steady-state L-T4 replacement dose disease were published in Endocrine Connections.



The study revealed that substitution dose was independently associated with gender, age, aetiology of hypothyroidism and total deiodinase capacity (SPINA-GD, all p<0.001). Stratifying patients by deiodinase activity categories of <23, 23-29 and >29 nmol/s revealed an increasing FT3-FT4 dissociation; the poorest converters had the lowest FT3 concentrations in spite of highest dose and circulating FT4 levels (p<0.001).



According to the authors these findings imply that a) thyroid hormone conversion efficiency is an important modulator of the biochemical response to levothyroxine, b) FT3 concentrations may be an additional treatment target, and c) L-T4 dose escalation may have limited success to raise FT3 appropriately in some cases.

Cover image: FT4 levels depend on diagnosis and SPINA-GD [Midgley et al. 2015]

References

Midgley JE, Larisch R, Dietrich JW, Hoermann R. Variation in the Biochemical Response to L-Thyroxine Therapy and Relationship with Peripheral Thyroid Hormone Conversion. Endocr Connect. 2015 Aug 11. pii: EC-15-0056. [Epub ahead of print] PubMed PMID: 26265111. doi 10.1530%2FEC-15-0056