TOPLINE

Children with idiopathic subclinical hypothyroidism (SH) demonstrated subtle left ventricular diastolic dysfunction characterised by prolonged isovolumic relaxation time (IVRT), which normalised after 2 years of levothyroxine replacement therapy.

METHODOLOGY

• Researchers in Italy conducted a prospective case-control study to compare left ventricular morphology and function between children with idiopathic SH and euthyroid control participants and to assess cardiac effects of levothyroxine therapy.
• They included 36 children with mild persistent and idiopathic SH (mean age, 8.25 years) and 36 matched euthyroid control participants (mean age, 8.27 years).
• Children with SH had thyroid-stimulating hormone (TSH) levels between 5 and 10 mU/L and free thyroxine (FT4) levels within the normal range for at least 2 years; no thyroid antibodies and normal thyroid ultrasound; no palpable goitre, hypothyroidism symptoms, chromosomal abnormalities, or chronic diseases; and adequate urinary iodine excretion.
• Children with SH received levothyroxine therapy at an initial dose of 50 μg/d (1-2 μg/kg/d), with dosage adjusted to maintain TSH and FT4 levels within reference ranges, and control participants did not receive treatment.
• Left ventricular morphology and systolic and diastolic function parameters were assessed at baseline and after 2 years of levothyroxine therapy in children with SH and after a 2-year follow-up in control participants.

TAKEAWAY

• Children with SH demonstrated a significantly prolonged IVRT compared with euthyroid control participants (92.95 vs 76.13 ms; P < .0006); however, other diastolic function parameters were similar between the two groups.
• From baseline to 2 years after levothyroxine therapy, the IVRT significantly decreased from 92.95 to 81.43 ms in children with SH (P = .004); it reached values comparable to those of control participants after 2 years of follow-up.
• No significant difference was observed between children with SH and euthyroid control participants in terms of left ventricular systolic function measured as left ventricular ejection fraction and ejection time.
• Left ventricular chamber dimensions, volumes, wall thickness, and indexed mass increased similarly and remained comparable between the two groups, staying within normal ranges for age.

IN PRACTICE

"The results of this study provide evidence of subclinical early diastolic dysfunction without increased LV [left ventricular] filling pressures in children with mild and persistent untreated idiopathic SH," the authors wrote.

SOURCE

This study was led by Michele Arcopinto, Department of Translational Medical Sciences, University of Naples Federico II, Naples, Italy. It was published online on July 30, 2026, in the Journal of Endocrinological Investigation.

LIMITATIONS

The study had a relatively small sample size. The study did not include an untreated SH comparator group that were followed up for the same 2 years, which would have allowed for a clearer distinction between the effects of levothyroxine and the natural course of the condition.

DISCLOSURES

This study received open access funding from the Università degli Studi di Napoli Federico II. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.