Transient vs Permanent Congenital Hypothyroidism: Does Thyroid Volume Tell the Tale?

Congenital hypothyroidism (CH) can be transient or permanent. We evaluated if thyroid volume measured by ultrasound can be distinguish between the 2 forms.

Retrospective study (1/2005-12/2019) on patients with CH with eutopic thyroids. Permanent CH was defined as the inability to discontinue levothyroxine therapy after age 3, while transient CH included a successful trial off levothyroxine. Demographic and clinical characteristics were retrieved from the electronic medical records. Fisher's Exact tests and t-tests were used to compare categorial and continuous variables between children with transient and permanent CH. Receiver-operating characteristic curve analysis evaluated thyroid volume and thyroid-stimulating hormone (TSH) as individual predictors of transient/permanent CH. A classification tree analysis was used to combine thyroid volume and TSH for prediction.

Significant differences were found between the 2 groups in terms of TSH levels and thyroid volume. Thyroid volume in patients with transient CH was significantly smaller (1.0 ± 0.5 mL) compared to those with permanent CH (2.3 ± 2.6 mL). No transient CH patient had thyroid volume below 0.3 mL or above 2.5 mL. Combining TSH level at diagnosis of ≥200 mIU/L and thyroid volume ≤0.6 mL or ≥2.5 mL provided sensitivity of 78.4% and specificity of 85.7% in differentiating between transient and permanent CH.

Thyroid volume ≥2.5 mL or ≤0.36 mL was seen only in permanent CH, potentially avoiding the need for a trial off levothyroxine. Using both TSH level and thyroid volume provides increased sensitivity and specificity for differentiating between permanent and transient CH.