Transient secondary hypothyroidism and thyroxine binding globulin deficiency in leukemic children during polychemotherapy: An effect of L-asparaginase

Abstract

Recently it has been observed that L-asparaginase causes transient thyroxine binding globulin (TBG) deficiency in adults. In the present study we investigated the influence of L-asparaginase on the pituitary-thyroid axis and on the synthesis of TBG. 14 children with acute lymphoblastic leukemia were treated with a combination of L-asparaginase, vincristine, prednisone and daunomycin for remission induction. Thyroid function was monitored by measuring total T₄, free T₄, total T₃, TSH and TBG with specific radioimmunoassays before, during and after treatment. Within 3 weeks of L-asparaginase therapy total T₄ fell significantly from 10.7±1.6 to 2.9±1.8 μg/100 ml, free T₄ from 1.77±0.4 to 0.94±0.35 ng/100 ml, total T₃ from 0.99±0.23 to 0.35±0.2 ng/ml and TBG from 29.4±3.6 to 8.0±3.8 μg/ml. Basal TSH values tinuation of L-asparaginase, but following further treatment with other antileukemic agents, all values became normal within 2–4 weeks. In 6 patients with hypothyroid free T₄ values TRH induced TSH release was totally blocked during L-asparaginase therapy. Our data clearly demonstrated that L-asparaginase caused a transient TBG deficiency. Total T₄ and T₃ were in the hypothyroid range because of low TBG concentrations. In addition to TBG deficiency transient, secondary hypothyroidism occurred in approximately 40–50% of all patients treated with L-asparaginase. These alterations were most likely caused by drug induced inhibition of protein synthesis. Under certain circumstances thyroid hormone replacement might be life-saving in severely ill patients suffering from transient, drug induced hypothyroidism.