Reports incorporating pituitary function testing in infants with non-thyroidal illness (NTI) are rare. Here, we describe the case of an infant (a 1-year-3-month-old boy) with failure to thrive secondary to inappropriate feeding practices. The infant developed NTI and reduced IGF-1 levels. He exhibited markedly impaired growth velocity, with low free triiodothyronine (T3), free thyroxine (T4), and insulin-like growth factor 1 (IGF-1) levels despite normal thyroid-stimulating hormone (TSH) levels and intact anterior pituitary responses on stimulation testing. Neuroimaging revealed no structural abnormalities. Upon nutritional rehabilitation with age-appropriate caloric intake, he exhibited catch-up growth and normalization of thyroid function and IGF-1 levels. This case demonstrates that NTI and low IGF-1 levels may occur in infants with malnutrition. The pathophysiology of NTI involves inflammatory cytokine-mediated alterations, suppression of hypothalamic-pituitary-thyroid axis regulation, and hypoleptinemia during starvation. Low IGF-1 levels reflect growth hormone (GH) resistance, mediated by fibroblast growth factor 21, and reduced insulin and leptin signaling. This case highlights the necessity of evaluating the nutritional and clinical background when assessing endocrine abnormalities to avoid misdiagnosing intrinsic pituitary or thyroid disease. Prompt nutritional intervention is critical for restoring growth and endocrine homeostasis. This case provides insights into the interrelationship between malnutrition, thyroid function, and growth regulation during early childhood.
Shimazaki et al. (Fri,) studied this question.