Congenital iodine-deficiency
ICD-10 E00 · ICD-11 5A00.04

Treatment of Congenital Iodine-Deficiency with Coexistent Central Adrenal Insufficiency (Central CH — Low or Normal TSH)

Clinical Scenario

Central congenital hypothyroidism (central CH) presents with low serum fT4 alongside a TSH that is low, normal, or only slightly elevated — a pattern distinct from the high TSH seen in primary hypothyroidism. In this scenario, coexistent central adrenal insufficiency is present or cannot be ruled out, which fundamentally shapes how treatment must be sequenced.

Coexistent Condition: Central Adrenal Insufficiency

When low fT4 occurs with a low, normal, or slightly elevated TSH, central CH should be considered. The presence — or inability to exclude — coexistent central adrenal insufficiency introduces a critical safety constraint: initiating thyroid hormone replacement before this condition is addressed carries a risk of precipitating an adrenal crisis.

Treatment Approach (Partial Overview)

Treatment in this setting requires that glucocorticoid therapy be established before thyroid hormone replacement is initiated — to prevent a potentially serious adrenal complication. The full protocol specifies the sequencing, the conditions under which each step may proceed, and the criteria that determine readiness to advance.

Treatment Goal

The biochemical target is bringing and maintaining serum fT4 in the upper half of the age-specific fT4 reference interval.

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References

DOI: 10.1089/thy.2020.0333

If the serum fT4 is low, and TSH is low, normal or slightly elevated, the diagnosis central CH should be considered.

In neonates with central CH, we recommend to start LT4 treatment only after evidence of intact adrenal function; if coexistent central adrenal insufficiency cannot be ruled out, LT4 treatment must be preceded by glucocorticoid treatment to prevent possible induction of an adrenal crisis.

In case of untreated adrenal insufficiency, LT4 treatment may cause an adrenal crisis.

Therefore, LT4 treatment should be started only after a normal adrenal function test result or after glucocorticoid treatment has been started.

The (biochemical) LT4 treatment aim is bringing and keeping the fT4 concentration in the upper half of the age-specific fT4 reference interval.

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