Endocrine Abstracts

Background: Levothyroxine is the standard treatment for central hypothyroidism (CH). Studies assessing the optimal dose are limited and include subjects with other untreated pituitary hormone deficits, affecting the interpretation of results. A reliable comparison with the dose used in primary hypothyroidism (PH) has not been reported.

Aims: To evaluate daily and body-weight-adapted levothyroxine dose (BWA-dose) in a cohort of patients with CH on appropriate replacement for concomitant pituitary deficiencies and to compare the dose in subjects with CH and PH matched for age, gender, BMI and FT₄.

Patients and methods: Seventy-one patients (41 males, age 53.1±14.6 years) with CH and normal FT₄ on a stable levothyroxine dose for at least 8 weeks were retrospectively reviewed. Other pituitary deficiencies were adequately treated. A subgroup of 65 subjects was compared with 65 patients with PH on levothyroxine and normal FT₃, FT₄ and TSH.

Results: In CH, median levothyroxine dose was 100 μg/day (range 50–225) and mean BWA-dose was 1.33±0.4 μg/kg per day. Patients with FT₄ in upper-half of reference range received higher BWA-dose than those with FT₄ in lower half: 1.45±0.4 vs 1.2±0.4 μg/kg per day (P<0.05). The BWA-dose negatively correlated with age and BMI (r=−0.325; P<0.01/r=−0.298; P<0.01, respectively). Patients with BMI>30 kg/m² or age>65 were replaced with a lower dose compared with those with BMI<30 kg/m² (P<0.005) or age<65 (P<0.01).

Comparison between CH and PH subjects did not reveal difference in levothyroxine dose.

Conclusions: Patients with CH on appropriate replacement of other pituitary hormone deficits require mean levothyroxine BWA-dose of 1.45±0.4 μg/kg per day to achieve FT₄ within the upper half of normal range. The mean BWA-dose to achieve FT₄ within reference range does not differ from that required for adequate replacement in PH.