Clinical studies on thyroidal autoantibodies

Studies on thyrotrophin receptor antibodies in patients with euthyroid Graves' disease

Thyroid stimulating antibodies (TSAb) and TSH-binding inhibitor immunoglobulins (TBII) were assessed in 30 patients with euthyroid Graves' disease. TSAb were detected in 24 cases (80.0%), the incidence being not significantly different from that in hyperthyroid Graves' disease (29/30, 97.6%). On the other hand, the incidence of TBII in patients with euthyroid Graves' disease (12/30, 40.0%) was significantly lower than that in patients with hyperthyroid Graves' disease (30/30, 100.0%). The mean TSAb and TBII activities in the euthyroid patients were significantly lower than in the hyperthyroid patients (P less than 0.005 and P less than 0.001, respectively). Both TBII and, more closely, TSAb activities correlated with T3-nonsuppressibility and inhibition of serum TSH response to TRH stimulation. The findings supported the stimulation in vivo of the thyroid by these antibodies. Both antithyroglobulin and antimicrosomal antibody titres in euthyroid Graves' disease were significantly lower than in hyperthyroid Graves' disease (P less than 0.05, P less than 0.01, respectively). Goitre size was significantly smaller (P less than 0.001), and 99mTc thyroid uptake was significantly lower (P less than 0.001) in the euthyroid than in the hyperthyroid group. Thus, the reduced mass of thyroid tissues responding to the stimulators was considered to be one of the factors responsible for the euthyroidism despite the presence of TSAb. The high incidence of TSAb and relatively low incidence of TBII in euthyroid Graves' disease indicate that the presence of TSAb does not necessarily lead to hyperthyroidism and that the development of overt thyrotoxicosis may require augmentation of both TSAb and TBII.

Discrepancy between haemagglutination and radioimmunological techniques for measurement of serum thyroglobulin autoantibodies

Recently, it has been suggested that in some patients with autoimmune thyroid diseases the tanned red cell (TRC) method for detection of thyroglobulin autoantibodies (TgAb) is negative where TgAb measured by radioimmunoassay (RIA) show positive values. To investigate this further, patients with thyroid diseases, pernicious anaemia and a control group were studied for serum concentrations of TgAb by TRC and by quantitative RIA, calibrated against MRC Standard A65/93. Antibodies for microsomes (MAb) were measured immunofluoretically. There was in all patient groups (Hashimoto's thyroiditis (n = 41), Graves' disease (n = 50), idiopathic myxoedema (n = 12), euthyroid Graves' disease (n = 7), pernicious anaemia (n = 81) a discrepancy between TgAb measured by TRC and RIA, respectively, whereas there was a reasonable correlation between the presence of TgAb by RIA and the presence of MAb. A possible interference from antinuclear antibodies and rheumatoid factors was ruled out. There was no increased frequency of TgAb measured by RIA in the control group. Fractionation of TRC negative sera revealed macromolecular TRC-activity, whereas TgAb positive sera by both methods had almost exclusively RIA and TRC activity corresponding to IgG. Based on these results and others it seems that the TRC method for measurement of serum TgAb is of limited diagnostic value. Furthermore, the TRC method is in many cases not sensitive enough for screening for TgAb prior to measurement of serum Tg, which is of importance as this method shows false values in the presence of TgAb due to methodological interference.

A case report of myasthenia gravis associated with Hashimoto's thyroiditis

An unusual case of myasthenia gravis is presented. The disease was clinically established in a 71-year-old Japanese woman by an electromyographic, pharmacologic test and anti-acetylcholine receptor (anti-AChR) antibodies demonstrated in the circulating blood. The coexistence of Hashimoto's thyroiditis was diagnosed by the presence of a diffuse thyroid enlargement, anti-thyroglobulin and anti-microsomal antibodies and a lowered thyroidal 131I uptake. A delusion of persecution developed during the treatment with pyridostigmine and ephedrine chloride, but the symptom disappeared after discontinuing the use of ephedrine chloride.

Lack of influence of thyroid antibodies on thyroid function in the newborn infant and on a mass screening program for congenital hypothyroidism

Data regarding the incidence and effect of maternal thyroid antibodies on neonatal thyroid function are conflicting. In order to elucidate this aspect, antimicrosomal thyroid antibodies were measured: (1) in cord serum of a normal populations, (2) in the eluate of blood spots of infants with normal filter paper spot T4 and TSH, (3) in the eluate of blood spots from our recalled population (low T4 and normal TSH), and (4) in serum of detected hypothyroid infants. The incidence of MCA with titer greater than 1/40 in cord sera was 8% (115 of 1.383). There was no statistical difference in cord serum T4' T3' or TSH concentrations in these newborn infants compared to the MCA negative population. In 1,000 spots with normal T4 and TSH, 11 or 1.1% were positive for MCA. In 1,630 spots with low T4' 18 positive cases were discovered, or 1.1%. There was excellent correlation between maternal MCA titers and newborn infant titers either in sera or spots when paired samples were available. Finally, only one of 104 detected infants with primary hypothyroidism had detectable MCA. These results indicate a high incidence (8%) of MCA in our presumed normal newborn population, MCA does not decrease serum T4' T3' and TSH concentration or filter paper spot T4 and TSH, and thyroid autoimmunity is not a frequent cause of congenital hypothyroidism.