INSUFFICIENCY OF LEVOTHYROXINE THERAPY IN AUTOIMMUNE HYPOTHYROIDISM: EFFECT OF GLUCOCORTICOID ADMINISTRATION.

Objective: The non-effectiveness of levothyroxine administration in hypothyroidism depends on many factors and mechanisms influencing its absorption in small intestins or bounding of circulating hormone with different active molecules.

Methods: Thyroid hormones, TSH, rT3, TGl, TPO-Ab, TG-Ab, were measured using commercially available assays. For anti-T4ab, radioiodine-labeled T4 was added to the patient's serum and the IgG fraction subsequently precipitated by addition of 15% polyethylene glycol. Background was determined by testing 100 control sera from individuals without autoimmune thyroid disease.

Results: A 42-year old woman (71.5 kg) with Hashimoto thyroiditis receiving levothyroxine (L-T4) 150 µg and liothyronine (L-T3) 37.5 µg was admitted to the hospital with clinical data of hypothyroidism, TSH-23.8 mU/L, FT4-6.18 pmol/L (n.range 9-19 pmol/L), TPO-Ab 696 IU/mL, TG-Ab 818 IU/mL, circulating T4- antibodies positive. She has a good adherence to medication, malabsorption or administration of other drugs were excluded. L-T4 absorption test revealed 44% increase of serum FT4 at 120 min after ingestion of 150 mcg L-T4 (2.1 mcg/kg). Methylprednisolone pulses of 500 mg i.v. administered in three consecutive days at equal doses of L-T4/L-T3 resulted in a rapid increase of FT4 to 14.5 pmol/L, fall of TSH to 0.18 mU/L and decrease of anti-T4 antibodies to referent range; TPO-Ab and TG-Ab also decreased significantly. Monotherapy by 150 mcg L-T4 was continued in the next three months. A recurrence of hypothyroidism with increase of circulating T4-Ab was observed 100 days later. New administrations of methylprednisolone two pulses of 500 mg revealed a similar normalization of thyroid hormones and anti-T4 antibodies.

Conclusion: The data showed that T4-antibodies might be a cause of insufficient effects of levothyroxine therapy in autoimmune hypothyroidism. This could be overcome by glucocorticoid administration probably resulting in FT4 release from circulating immune complexes.