Patterns of TSH response to TRH in children with hypopituitarism

The TSH response to TRH was studied in 42 children with hypopituitarism. Basal TSH was similar to the control group except in seven patients who had elevated values (Group A). These children also had an altered TSH response to TRH but normal increments in T 4, T 3, and 131I thyroid uptake after administration of bTSH. Three different patterns of TSH responses to TRH were observed in patients with normal basal TSH: delayed and exaggerated response (Group B, n=15), deficient response (Group C, n=4), and normal response (Group D, n=16). Some patients of groups A, B, and C with blunted basal growth velocity had an improved growth rate with T 4 therapy. However, a better response was observed when hGH and T 4 were administered simultaneously. The following conclusions were drawn: (1) high immunoreactive TSH in the presence of a thyroid gland responding normally to TSH suggests a dissociation between the biologic and immunologic activity of serum TSH; (2) an exaggerated and delayed response to TRH was frequently found in secondary hypothyroidism and suggests hypothalamic TRH deficiency; (3) an impaired TSH response to TRH is less frequent and suggests a pituitary abnormality; (4) patients with a normal response to TRH probably have normal hypothalamic-pituitary thyroid axis. The TRH test is useful in the diagnosis of hypothalamic-pituitary thyroid abnormalities and helps to unmask thyroid dysfunction. A number of such patients with stunted growth benefit from thyroid therapy.