Endocrine Abstracts

Chronic administration of L thyroxine to children with hypothyroidism may affect cardiovascular dynamics.

Aim of the study: We measured the BP and heart rate (HR) of 25 randomly selected children with hypothyroidism in relation to their serum free T4, and TSH levels and thyroxine dose mg/kg.

Methods: 25 randomly selected children with a mean age 9.6 +/- 4.5 years with the diagnosis of congenital or acquired hypothyroidism. They were on L thyroxine therapy to keep serum FT4 and TSH in the normal range for age. Their blood pressure (BP) and HR (average of three readings), weight, height, dose of thyroxine, and their serum level of TSH and Free T4 levels within two weeks before the clinic visit were recorded. The Z scores of the height (HtSDS), BMI (BMISDS), systolic (SBPSDS) and diastolic blood pressure (DBPSDS) were calculated (as per the 2004 guideline report on hypertension from the National Heart and Lung institute) and HR (as per the Monitoring and Diagnosis Group at Oxford (MADOX) systematic review of 2011) were calculated for age and gender.

Results: L thyroxine dose was 2.11 +/- 0.7 mg/kg. Their mean serum free thyroxine levels was 15.1 +/- 2.5 mg/l and TSH level was 3.9 +/- 2.8 mIU/ml. Their HtSDS (-0.57 +/- 1.4) and BMISDS (0.63 +/- 1.63) were within normal. All had normal diastolic blood pressure readings (within 2 standard deviations of the mean for age and sex). Two of the individuals had systolic blood pressures > 2SDS above the mean for age and gender, with normal BMISDS. Both had normal FT4 and TSH levels. One patient had tachycardia (HR = 146/min (z score +3.2 for age). His FT4 and TSH levels were normal. There was a positive correlation between thyroxine dose/kg and serum level of FT4(r=0.52), heart rate (r=0.56), SBPSDS (r= 0.38), and DBPSDS (r=0.24). There was no significant correlation between the HtSDS on the one hand and FT4, TSH or thyroxine dose on the other hand. The BMISDS was negatively correlated with TSH level (r=-0.4)

Conclusion: In this study on hypothyroid children on L thyroxin therapy, 2 had high systolic blood pressure and one had tachycardia. The significant correlation between the thyroxine dose, FT4 level and BP and HR should alert the Pediatrician to monitor BP and HR closely in relation to TSH and FT4 levels these patients.