medwireNews: A longitudinal study of Finnish patients with juvenile acquired hypothyroidism (JHT) has revealed that an abnormal growth pattern may be present for up to 5 years before diagnosis.
Lead investigator Antti Saari, from Kuopio University Hospital in Finland, and colleagues say that the “distinct” patterns of height and weight in this population “could be an early sign of thyroid autoimmunity” and may potentially help with early detection of the condition.
As reported in The Journal of Clinical Endocrinology & Metabolism, the team collated 554 height and weight measurements taken in the 5 years before diagnosis of JHT in 109 patients (75% female) based on a thyroid stimulating hormone concentration above 10 mIU/L on at least two occasions in combination with clinical symptoms or thyroid peroxidase autoantibodies.
At time of diagnosis, patients were aged a median of 10.6 years (range, 1.2–15.6 years) and 52.3% had at least one symptom, most commonly fatigue or dizziness (31.2%), skin problems (25.7%), stomach pain (19.3%) or increased sensitivity to the cold (8.3%).
The patients were then matched by age and sex to 10,900 healthy children and this revealed that at the time of JHT diagnosis, the patients were heavier and shorter than the controls, with a mean adjusted BMI standard deviation score (SDS) difference of 0.65 and a height SDS deviation from target height SDS (THDEVSDS) of –0.35.
The greatest difference in change in height SDS was found in the year before JHT diagnosis, with a mean difference of –1.06 that continued to be statistically significant after taking into consideration perinatal factors.
And 2 years before diagnosis, there was significantly slower linear growth in the JHT cohort than the control group, with a mean adjusted change in height SDS difference of 0.53.
But although JHT patients were also heavier than the healthy individuals 5 years before their diagnosis (mean difference 0.44), at this point the patients were taller than the controls, with a height SDS difference of 0.32.
The team assessed the ability of five different growth parameters to identify JHT in the patient population: BMI SDS; THDEVSDS; change in BMI SDS over time; height SDS; and change in height SDS over time.
Individually each parameter had only a poor-to-moderate ability to identify JHT among patients but when these factors were combined, the researchers were able to identify growth failure at diagnosis in JHT patients with “good” accuracy, with an area under the curve of 0.83.
Using a cutoff of 1.7 SDS for short height and increased weight, the combination of the five parameters was able to detect JHT with 58% sensitivity and 87% specificity, with corresponding values of 25% and 98% when using a 2.7 SDS threshold.
“A significant number of children and adolescents diagnosed with JHT could have been detected using longitudinal growth monitoring and auxological screening with pre-established cut-off values, methods that are simple and non-invasive”, say Antti Saari and co-authors.
They believe that for JHT the “relatively low specificity can be deemed acceptable because cases are investigated further using inexpensive and widely available thyroid function tests.”
But the team admits that the current study was unable to follow up patients to determine what impact JHT and levothyroxine treatment might have on adult height.
“Early detection of JHT is important not only for neurocognitive development but also for preventing a permanent height deficit resulting from thyroid hormone deficiency”, Saari et al conclude.
By Lynda Williams
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