Lean body mass based levothyroxine supplement lessens deterioration of cardiac function and exercise capacity in radioiodine ablated differentiated thyroid carcinoma patients

Abstract

Conventional supplement therapy of levothyroxine (LT4) for differentiated thyroid carcinoma (DTe) keeps the patient in sllbclinical hyperthyroid stale, which affects the heart activity and lowers exercise capacity. Lean body ma% (LBM) hM been recently suggested as best determinant of LT4 supplement dosing in palientq with DYC. The present study was done to optimize the dose of LT4 in low ri.\k group (Tl, NO, MOl of patients with D1 C ~nd thereby preventing the adverse cardiac effects and improve exercise capacity. The importance of dose adjustment of LT4 based on lean body mass ba., not been properly addressed before. Sixty patients with differentiated (papillary) thyroid carcinoma (young age group) witho>.!!any signs of melaltases, previous cardiac problems and chronic di,casc w= conseClltively enrolled in the study. They were referred to Institute of Nuclear Medicine and Ullra>ound, Dhaka during the year 2007-2009 from different district Hospitals of Bangladelh. All patlents had undergone tOlal thyroidectomy and then received about 100 m ei radioiodine ablative therapy and ,ubsequently 200 I-'gm L1'4 daily for initial 2 months, Age, weight, height, body surface area, body mass index and hfe style matched 23 healthy euthyroid voluntc-ers were also selected. All clinical, biochemical, echocarrliographic and Exercise Tolerance Te~t (ETI') data of healthy adults control Were oblained for companIon with patients at baseline study after two months of radioiodine ablative therapy and On I ,1'4 rep1a~ement on convenlional 200 I-'!,'IIl!day at first follow up visit. Then 60 palient, were grouped "-\ Group-I and Group-H, eHch group consisted of 30 paticntl. l1lirly patienls of GrolIp-1 had undergone dual energy Xray absortiometry (DXA) investlgation to estimate lean body ma% and received optimized L'J'4 dose depending on lean body mass (about lJH 23 fl grn/day, 3.5-41-' gm/kg! J .Blv1!rlay).In Group-ll, 30 patients wntulUc,j the conventional fixed dosc of L1'4 (200 I-'gm/day). Patients of both groups were followed IIp clinically and hormone ,,-~,\aywere done at 3 months interval, At 6,12 months of LT4 supp1cment (convClltional and LBM based) aU stlIdy paramelers (Symptom Rating SLWe, hormone data, echoCfll'diogl'aphicdata and ETT) wcre reevaluated. SelUIll fT3 (Group-I, 5.5;t1.3 p moUL; Group-H,1O.1:t1.3 p molfL, *]' < 0.00l), Ff4 (Group-l,17.9 ;loL9p moUL; Group-H, 27.4:1:0.94p moUL; *1'< 0.001) Were higher and 1'SH (Group-I, O.lw.OJ mIU/L; Group-II, 0.09;tO.05 mlUlL; ~1' < 0.001) Wa.1 suppressed in patients with D1'C at conventional IT~ dose (200 I-'gmlday) compared to healthy control and patients witb oplimiLed dose of L1'4 (mean"SD, 131* 23 )lgm/day) of Group-l at second visit. Symptom Rating Scale score (SRS, Grollp-l, 2:t1, Group-II, 8;lo1, at second vhit; *1' < O.OOJ), heart rate (Group-I, 87:t14 beat>!min, Group-lI, 100:t20 bpm, at second visit; *1' < 0.003). SliP (Group-I, 1I4:t7 mm Hg, Group-H, 119:t8 mIll Hg, at second visil), DUP (Group-I, 75,,7 mm Hg, Group-H, 78:t4 mm Hg, at lecond vi;i!) were slightly higher in patient$ (Group"Il) aftel' receiving conventional L1'4 suppressive dose but were not statistically significant. Left ventriculal' ma.~.1(LVM) (*1'<0.05), left ventricular mass index (LVMi) (*1'<0.01), fraction shOitening (FS%) xvi (~p<O,OOl) and heart rate adjusted mean velocity of circumferential fiber shortening (mVCFc) (*p<O.OOJ) were increm;ed in patients of Group-T1 after e~pOSUTeof conventional LT4 do,e compared to patIents received optinnzcd dose (Group-I) at ~econd visit. Ejection time was also decreased in patients of Group-II at second visit compared to patients of Group-I at first visit ~P<O.Ol,Mild degree of diastolic function abnormalities were also noted in Group-II patients at second vi~it compared to Group-I patients. Early (E) dia>lolic velocity of Group-IT was significantly low at second vi~it compared to that of Group-I at first visit (*p<O.005) and late (A) was comparatively high in group 11compared to Gl'oup-I at second vi,it (A, Group-I, 51:108crn /sec, Group- IT, 58:!:8 em fsec; *p<O,Ol). Deceleration time (Oct) was significantly low in Group-TT compared to patients in Group-I at two visits and patients of Group-II at fillt visit (Oct, Group-I, 155:1016m sec, Group-H, l27:!o18 m sec; *p<O.OOl). Similarly in tiloSlle Doppler imaging technique, late diai>tolic mitral annular velocity (Am) wa, higher in Group-IT compared to Group-I at second visit (Am, Group-I, 15:103em Isec, Group-II, 19:106cm Isec; *p<O.003). Signific'lTlliy high modified Tei index was also noted in patients of Group-IT at second visit compared to their finn viSIt value and patients of Group-I at different VISIts (Group-I, O.34:!:O.08;Group-II, 0.48:tO,06 at sccond visit *p<O.OOl). Excrcisc capacity as evaluated by excrcise toler~llce test (Erl'), ,howed signifICant diffcrenee (*p<O.05) ill metabolic equivaknt (MET) between healthy voluntccrs and patients groups at fit'st visit hut no difference was found between two paticnt groups at different time points, It is concluded that uptimization of do>,eof LT4 based on lean body lIla" Can avoid chn.mic exposure of mild e•.cess of lhyroid hOIDlOnein the body and Improve qualily of life in patient\ with low risk DTC by prevcnting a:nd minimizing adversc cardiac erfects.