Vishnugirish,Dr.Somashekar, *Dr.Chandrika Rao M.S.Ramaiah Medical College and Hospital Bangalore. ‘Cognitive performance and thyroid hormone levels in adolescents with subclinical hypothyroidism'

Introduction Subclinical hypothyroidism(SCH) is characterized by increased TSH levels in presence of normal T4 or T3. It can negatively affect cognitive functioning.

Objectives To correlate serum T3,T4,TSH with adolescent`s cognitive performance on a learning disability scale.

Methods Cross sectional study 100 schoolchildren, age group 10 – 15 years. Informed consent. Inclusion criteria-Healthy Exclusion criteria- criteria-Illness,Drugs,Diabetics, Epilepsy, Anemia history of thyroidectomy, Head injury, L – thyroxine therapy. T 3, T 4 and TSH were estimated. NIMHANS index for Specific Learning Disability- language, arithmetic, visual-motor skills and memory. Two groups – euthyroid and subclinical hypothyroid.

Methods This data was collected by personal interview method. The number of mistakes made in each component of the index as well as the total number of mistakes made was recorded. This was used to compare with their thyroid hormone levels. The investigator administering NIMHANS scale was blinded to thyroid hormone levels.

Statistical analysis SPSS Student `t` test was employed to test for the difference in mean values between euthyroid and SCH. The descriptive statistics on SLD score were analysed and expressed in median,Significance- Mann Whitney U test. The Spearman Rank correlation between TSH, T3 and T4 in euthyroid and SCH and the number of mistakes made in the NIMHANS index for SLD was calculated Both zero order correlation coefficient and partial correlation coefficient(controlled for age) were estimated.

Results 62 -girls and 38-boys. The socioeconomic background and education of parents were similar in the sample studied. 21 subclinical hypothyroid,79 euthyroid. No goiter,subclinical hyperthyroidism or any clinical manifestations of thyroid disorder.

Components Median Subclinical hypothyroid Median (Range) Euthyroid Median (Range) Language8.00 (6.00, 11.50)7.00 (5.00,12.00) Arithmetic11.00(6.50,1200)9.00(6.00,12.00) Visuo – motor skills8.00(4.00,11.00)6.00(4.00,8.00) Memory3.00(2.00,5.00)3.00(2.00,4.00) TOTAL26.00(21.50,38.00)25.00(22.00,31.00) Subclinical hypothyroid group made more mistakes when compared to the euthyroid group.

Thyroid Status LanguageArithmeticVisua- motor skills Memory T3 EuthyroidP=0.014P=0.006P=0.005P=0.003 T3 Sub-hypoP=0.082P=0.166P=0.122P=0.117 T4 EuthyroidP=0.000 T4 Sub-hypoP=0.105P=0.000 TSH EuthyroidP=0.535P=0.430P=0.832P=0.753 TSH Sub-HypoP=0.531P=0.280P=0.241P=0.151 MALES -T4 levels correlated in all areas except in language. TSH did not correlate.(gender and age adjusted)

Thyroid status LanguageArithmeticVisuo-motor skills Memory T3 EuthyroidP=0.995P=0.053P=0.132P=0.206 T3 SCHP=0.859P=0.313P=0.569P=0.597 T4 EuthyroidP=0.000 T4 SCHP=0.280P=0.000 TSH EuthyroidP=0.241P=0.442P=0.399P=0.514 TSH SCHP=0.928P=0.799P=0.752P=0.792 Females-T4 levels correlated in all areas except in language. TSH did not correlate.

Discussion In the brain T3 is mostly derived from local T4 deiodination (D2 and D3). In thyroid deficiency, increased D2 activity maintains normal T3 concentration despite reduced T4 concentrations in brain. Thyroid hormones are present in CSF at less than ten times the serum concentrations. The findings of this study point out that both T3 and T4 should be tested with TSH in adolescents. There are contrary reports of treating SCH. However in a SCH adolescent who is in the threshold of higher studies, decreased cognitive function may be a determent to achieve high standard in academic.

Limitation 1.Small sample size of SCH children. 2.Only one blood sample value was taken and transient SCH or diurnal variation was not considered. 3. We have not studied cognitive abilities after therapy in SCH children.

CONCLUSION T3 and T4 levels have correlation with cognitive skills compared to TSH. Hence,it is necessary to measure both T3 and T4 in addition to TSH in adolescents.

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