Endocrine Abstracts

Background: TSH secretion shows a diurnal rhythm with a surge in the evening. The nocturnal surge is essential for thyroid function regulation. TSH surge is suggested to be blunted in central hypothyroidism. In idiopathic short stature (ISS), thyroid dysfunction has been suggested ranging from mild hypothyroidism to central hypothyroidism.

Aim of the work: To study the pituitary thyroid axis and the TSH surge in ISS.

Materials and methods: Thirty subjects (10–18 years old) diagnosed as ISS and thirty matched normal controls were chosen for the study. Thyroid function tests were measured in the basal state, namely T₄,T₃, and TSH. TSH was then measured for each subject at 1000 , 1900, and 2200 h. A peak nadir levels were determined TSH surge (peak-nadir/nadir) was expressed as percent rise over the nadir.

Results and conclusion: 33.33% of ISS patients had blunted nocturnal TSH surge (median 10.27) suggesting central hypothyroidism. 33.67% of ISS patients had mild elevation of TSH values and normal nocturnal RSH surge (169.30) suggesting mild hypothyroidism. The remaining 30% of ISS patients had normal thyroid functions and normal nocturnal TSH surge (77.140) as compared to control subjects (60.72) suggesting no role for thyroid dysfunction in this group.

TSH values were lowest at 1900 h in all groups except in mild hypothyroidism at 1000 h. The highest values of TSH were recorded at 2200 h in all groups.

To conclude, the study of TSH surge in ISS is a useful technique to diagnose associated central hypothyroidism and mild hypothyroidism. These patients could benefit from early treatment by levothyroxine.