Recovery of thyroid function in patients with both thyroid and renal dysfunction was studied. Among 245 patients with primary hypothyroidism (serum TSH >10 mU/l), 36 had mild to severe renal dysfunction (serum urea nitrogen >7.1 mmol/l and creatinine >106 μmol/l). Of these 36 patients, recovery of the thyroid function after iodine restriction was observed in 30(83%), in whom an elevated serum non-hormonal iodine level (median 236, range 67–15591 μg/l, N=19) and a high thyroidal radioactive iodine uptake (51.5±29.3%at24h, N = 26) were observed. The perchlorate discharge test was positive in 7 of 13 patients examined, suggesting an iodide organification defect rather than an atrophic or destructive change in the thyroid. Antithyroid antibodies were negative in 22 patients (73%) and an almost normal thyroid gland or colloid goitre was confirmed histologically in 8 of them. After a 13.2 mg potassium iodide loading test, 24 h urinary excretion of iodine was about 60% in normal controls, but only 10% in a different group of six euthyroid patients with renal dysfunction. These findings suggest that impaired renal handling of iodine rather than autoimmune mechanism may have a significant role in the pathogenesis of reversible hypothyroidism found in patients with renal dysfunction, probably through a prolonged Wolff-Chaikoff effect.

The clinical significance of the thyroidal radioactive iodine uptake (RAIU) test was reevaluated in patients with various thyroid disorders. Compared with 262 normal subjects or 194 patients with euthyroid diffuse goiter with normal serum TSH levels, RAIU values were significantly higher in 100 patients with latent primary hypothyroidism (serum TSH, 5-40 mU/L). In 126 patients with overt primary hypothyroidism (serum TSH, greater than 40 mU/L), RAIU values were either extremely high (49 patients with reversible hypothyroidism and 10 patients with postpartum hypothyroidism) or low (67 patients with irreversible hypothyroidism). The increase in RAIU values in latent, or reversible overt hypothyroidism was TSH dependent, and there was a good correlation between RAIU values and serum TSH levels (r = 0.6203; P less than 0.001). In overt primary hypothyroidism, spontaneous recovery of thyroid function during iodide restriction alone occurred in 52 of 53 patients with RAIU values above 35%, in only 7 of 23 patients with RAIU values between 10-35%, and in none of 50 patients with RAIU below 10%. Thus, recovery was predicted by high RAIU values (P less than 0.001; prediction rate, 91.4%). Goiter was found in about 80% of the patients with reversible hypothyroidism, compared with only 34% of the patients with irreversible hypothyroidism. Recovery of thyroid function during iodide restriction also occurred in 71% of the patients with latent hypothyroidism. However, RAIU measurements did not predict the prognosis of patients with latent hypothyroidism. We conclude that iodine-induced reversible hypothyroidism is common in our patient population, and RAIU measurements may be helpful in determining the prognosis of patients with overt primary hypothyroidism.

We studied 2 men with a subacute thyroiditis-like syndrome (STLS) associated with systemic amyloidosis. Both had very tender, diffuse, firm goiters, low thyroidal radioactive iodine uptake values, and increased erythrocyte sedimentation rates. Glucocorticoid therapy resulted in dramatic improvement. Compared to 18 patients with subacute thyroiditis, these 2 men had 1) persistence of goiter even in remission, 2) repeated exacerbation of STLS, 3) pain always localized in the same site, and 4) gastrointestinal, renal, and cardiac abnormalities. Histological examination of the patients' thyroid glands revealed amyloid deposition and no evidence of subacute thyroiditis. In addition, 1 man had low T3 thyrotoxicosis with an elevated rT3/T3 ratio, suggesting impaired peripheral conversion of T4 to T3, and immunological and histological evidence of Hashimoto's thyroiditis. These findings suggest that thyroid amyloidosis may be associated with STLS. When patients with clinical features of subacute thyroiditis have an unusual course, the possibility of thyroid amyloidosis should be considered.

Thyroid stimulation indices such as high thyroidal radioactive iodine uptake, increased estimated thyroid weight, presence of TSH-binding inhibitor immunoglobulin or thyroid-stimulating antibody, and elevated serum thyroglobulin level, were evaluated in 148 patients with Graves' disease who had been treated with antithyroid drugs for two years or more before the drugs were withdrawn. In all 19 patients in whom three or more indices were positive, early relapse, within 12 months, occurred after reducing the dosage of antithyroid drugs. Other 129 patients were followed after the drug was withdrawn and in 77 patients with one or two positive indices, early relapse occurred in 65-71% and late relapse, after 12 months or later, occurred in 2-11%. In 52 patients in whom none of the indices were positive, 86% remained in remission, but 10% developed an early relapse, and 4% a late relapse. We conclude that a combined analysis of thyroid stimulation indices is useful in predicting relapse in Graves' disease whereas it remains difficult to predict permanent remission.Many tests or parameters including the TRH test (1-3), T3 suppression test (4-13), thyroid size (14-16), serum levels of thyroid-stimulating immunoglobulin (17)(18)(19) or thyroglobulin (Tg) (20-23) and T3/T4 ratio ( 11,24) have been used as predictive parameters of remission in Graves' disease. How¬ ever, none of these parameters is satisfactory by themselves.Recently Schleusener et al. (25) reported a pro¬ spective multicentre study on the prediction of re¬ lapse using various parameters such as TSH recep¬ tor antibodies activity, antithyroid autoantibodies, HLA DR typing, suppression test, TRH test, goitre size, age, and degree of ophthalmopathy. Although patients with positive TSH receptor antibody, ab¬ normal suppression or an abnormal TRH test, or a large goitre have a significantly higher relapse rate than those without, they concluded that the sensi¬ tivity and specificity of these paramters were too low to be useful for daily clinical decision in the treatment of an individual patient, even if the com¬ bination of different two parameters was analysed.Theoretically, activity in Graves' disease could be shown by the presence of thyroid-stimulating an¬ tibodies. Goitre size, thyroidal radioactive iodine uptake (RAIU) and serum Tg levels are also good parameters to show how the thyroid gland is stimu¬ lated, as shown in patients with diffuse goitre stimu¬ lated by endogenous TSH (26-28).

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