Nonthyroidal Illness Syndrome in a Noncritically Ill Child

Nonthyroidal illness syndrome (NTIS) is an endocrine phenomenon most commonly known from critically ill children admitted to the intensive care unit. NTIS is regarded as physiological adaptation during severe illness. It is characterized by low free triiodothyronine and free thyroxine (T4) concentrations with normal to low levels of thyroid-stimulating hormone in combination with the clinical context of the child. Distinction with central hypothyroidism can be difficult, especially in early childhood, where congenital hypopituitarism can present as well. Here we report NTIS in a noncritically ill boy, 10 months old in the outpatient clinic, with failure to thrive. Due to the noncritical illness and age, suspicion of congenital hypopituitarism was raised and thyroxine supplementation was started. Growth hormone deficiency could not be excluded. Corticotropic axis was found sufficient with very high levels of cortisol. After extensive diagnostics including a brain magnetic resonance imaging, which was normal, a neuroblastoma was diagnosed. After surgical resection of the neuroblastoma, thyroid function recovered and thyroxine supplementation was stopped successfully. This case demonstrates that NTIS can be present in young children with severe underlying disease but who are not critically ill. It emphasizes the importance of a thorough diagnostic workup in children with otherwise unexplained “central hypothyroidism.” When low free T4 is found with high cortisol, this is a red flag for the pediatrician pointing to severe underlying disease.