Natural history of primary myxedema.

It is generally admitted that primary myxedema in adults is the outcome of autoimmune atrophic thyroiditis. The present review traces the natural history of this process from its incipient biologic and genetic anomalies up to its protracted asymptomatic course, clinical development, and eventual lethal complications. The apprehension of preclinical hypothyroidism may change a clinician's outlook on early diagnosis and therapy.

Asymptomatic atrophic thyroiditis.

Asymptomatic atrophic thyroiditis (AAT), one of the three variants of autoimmune thyroiditis, is characterized by the presence of serum antithyroid antibodies in good correlation with thyroid lymphoplasmocytic infiltrations. AAT affects 5-15% of the general population and is especially prevalent in elderly women. Patients with AAT have no goitre and are clinically euthyroid. While circulating thyroid hormones are always in the normal range, peak TSH and TRH and basal TSH values are increased in two thirds of the cases. There is a familial aggregation of AAT and a frequent association with other autoimmune diseases. Development of overt hypothyroidism in AAT patients is not rare. Preventive thyroid replacement therapy is indicated in patients with elevated basal TSH levels.

Grades of subclinical hypothyroidism in asymptomatic autoimmune thyroiditis revealed by the thyrotropin-releasing hormone test.

Serum levels of T4 T3, and TSH and peak TSH after TRH administration were determined in 60 female subjects affected with asymptomatic autoimmune thyroiditis (AAT), in 27 normal subjects, and in 8 myxoedematous patients used as controls. The AAT subjects were divided into 3 groups on the basis of their basal and peak TSH values. In the first group (grade I AAT), these parameters were similar to those of the normal controls; in the second (grade II AAT), basal TSH remained normal but peak TSH was significantly increased; and in the third (grade III AAT), both parameters were significantly increased. Serum T4 levels decreased progressively from group 1 to group 3, but all T4 values were within the normal range. T3 levels were similar in all groups. Peak and basal TSH values were highly correlated, except in grade II AAT. There seems to exist a graded process of subclinical hypothyroidism in AAT; a progressive pituitary TSH reserve is modulated by a progressive decrease in T4 levels still within the normal range.

Asymptomatic autoimmune thyroiditis and coronary heart-disease. Cross-sectional and prospective studies.

Cross sectional and prospective surveys of thyroid autoimmunity have been performed in two cohorts of men, 280 living in west Finland and 269 in east Finland. In both populations, aged 50 to 69 years at the first survey, risk factors for coronary heart-disease (C.H.D.) were common. The incidence of C.H.D. was shown to be related to the presence of thyroid antibodies. The results of the cross-sectional studies were not conclusive. The five-year follow-up study emphasised that in both areas asymptomatic thyroid autoimmunity, independently of other known risk factors, was a predictor of subsequent development of C.H.D. The importance of asymptomatic autoimmune thyroid-itis as a risk factor for C.H.D. increases with age.

[Diagnosis of incomplete hypothyroidism]. / Diagnostic de l'hypothyroïdie fruste.

The clinical picture of mild hypothyroidism consists of mild, often non-specific signs. In general, the diagnosis can only be made in the laboratory. Estimations of protein-bound iodine, thyroxine and tri-iodothyronine in the serum are often within normal limits. A rise in serum TSH and in doubtful cases, the excessive liberation of TSH during the TRH-TSH test confirm the diagnosis. As mild hypothyroidism is often due to auto-immune thyroiditis, the demonstration of anti-thyroid antibodies may guide the clinician.

Pituitary-thyroid axis reaction after myocardial infarction.

Within the first 36 hours following myocardial infarction, serum total thyroxine (T4) levels were supranormal in most cases in contrast to normal thyrotropin values. After one week, T4 levels dropped to normal while TSH values rose significantly. These findings suggest that, in the acute phase of myocardial infarction, the secretion of thyroid hormones is increased, thereby inhibiting the pituitary thyrotropes. The stimulation of thyroid secretion might be due to the high levels of blood catecholamines generally found in patients with myocardial infarction.