Hashimoto's thyroiditis: Relative recurrence risk ratio and implications for screening of first degree relatives

Abstract

Context

The relative recurrence risk ratio (λ_R) for Hashimoto's thyroiditis (HT) has not been widely studied. The age at which thyroid function evaluation should be initiated for relatives of HT patients remains unclear.

Objective

To study λ_R and age-related prevalence of HT in first degree relatives of HT patients.

Methods

First degree relatives (n=861) of 264 HT patients were evaluated for goitre, thyroid function tests, thyroid antibodies (TAb) and urinary iodide concentration (UIC). HT was defined as TAb positivity and hypothyroidism (subclinical/overt). λ_R was calculated as {number of index patients whose relatives (of particular subtype) had HT/number of index patients having relatives of same subtype}÷ population prevalence of HT (5.1%). The age-related prevalence of HT was studied using Kaplan–Meier method.

Results

861 relatives (205 parents, 336 siblings, 320 off-spring) participated in the study. 38.3% were TAb positive. The prevalence of HT was 16.7% (22.9% in parents, 19.6% in siblings, 9.6% in offspring). TAb positivity (48.3% vs. 33.1%) and HT (23.5% vs. 13.6%) were significantly more common in the goitrous group (n=267) vs non goitrous group. The median UIC for the study population was 182.5 μg/L. Computed λ_R was 9.1 for any one relative being affected, 5.9 for parents, 6.3 for siblings, and 3.1 for offspring. The prevalence of HT increased with age and exceeded the adult population prevalence of 5.1% at 20 years in females and 27 years in males.

Conclusions

Relatives of HT patients have a 9 fold increased risk for developing HT as compared to the general population. The risk of developing HT exceeds that of the general population at 20 years in females and 27 years in males.

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