Effects of protracted hypothyroidism on pituitary function and structure in endemic cretinism

Cretinism presenting as a pseudotumour

A 43-year-old man from a remote part of India (over 1800 km from our institution), presented with a headache of 3 years duration. He was of short stature, had delayed puberty and was mentally retarded. On evaluation he was detected to have primary hypothyroidism with markedly elevated thyroid-stimulating hormone titres. A CT of the brain revealed a large sellar mass with suprasellar extension into the third ventricle causing obstructive hydrocephalus. Surgical intervention was deferred due to absence of visual impairment and the presence of gross hypothyroidism. The clinical diagnosis of congenital hypothyroidism was confirmed by the absence of radioiodine uptake in the thyroid bed. With thyroid hormone replacement therapy, the 'tumour' underwent significant reduction in size with the resolution of hydrocephalus thereby favouring a potential pituitary pseudotumour. This was an unusual situation of a giant pituitary pseudotumour detected in an adult with untreated congenital hypothyroidism.

The interrelationships between thyroid dysfunction and hypogonadism in men and boys

Thyroid hormone deficiency affects all tissues of the body, including multiple endocrine changes that alter growth hormone, corticotrophin, glucocorticoids, and gonadal function. Primary hypothyroidism is associated with hypogonadotropic hypogonadism, which is reversible with thyroid hormone replacement therapy. In male children follicle-stimulating hormone (FSH) is elevated and associated with testicular enlargement without virilization. Men with primary hypothyroidism have subnormal responses of luteinizing hormone (LH) to gonadotropin-releasing hormone (GnRH) administration and normal response to human chorionic gonadotropin (hCG). Free testosterone concentrations are reduced in men with primary hypothyroidism and thyroid hormone replacement normalizes free testosterone concentrations. In men with primary hypothyroidism, prolactin is not consistently elevated (except in men and children with longstanding severe primary hypothyroidism), but prolactin declines following thyroid hormone replacement therapy. Thyroid hormone is known to affect sex hormone-binding hormonal globulin (SHBG) concentrations. Men with hyperthyroidism have elevated concentrations of testosterone and SHBG. Thyroid hormone therapy in normal men may also duplicate this elevation. In addition estradiol elevations are observed in men with hyperthyroidism, and gynecomastia is common in them as well. In contrast to patients with primary hypothyroidism, men with hyperthyroidism exhibit hyperresponsiveness of LH to GnRH administration and subnormal responses to hCG. Radioactive iodine therapy (RAI) of men treated for thyroid cancer produces a dose-dependent impairment of spermatogenesis and elevation of FSH up to approximately 2 years. Permanent testicular germ cell damage may occur in men treated with high doses of RAI. RAI commonly increases serum concentrations of FSH and LH while reducing inhibin B levels without affecting serum concentrations of testosterone. Thus, radioiodine therapy transiently impairs both germinal and Leydig cell function that usually recover by 18 months posttherapy.

Endemic cretinism: toward a unifying hypothesis

Based on our data, the clinical picture of endemic cretinism results from the product of two pathophysiological events. Both events share a common feature, namely iodine deficiency, but act at different points in time. The first event occurs in all cretins and represents the prenatal action of thyroid hormone deficiency on brain development, transmitted vertically from mother to fetus, resulting in the neurological disorder of endemic cretinism. A consistent pattern and intensity of neurological, intellectual, and audiometric deficit is common to and equally present in all types of endemic cretin. The nature of these deficits points to an intrauterine insult to the developing fetal nervous system around the time of the midtrimester. The second event represents the postnatal action of thyroid hormone deficiency on somatic as well as brain development. Whereas previous workers had attributed the differences in the clinical presentation of endemic cretinism to the presence or absence of neurological features (i.e. prenatal hypothyroidism), the distinction between the types of endemic cretin can be related to the length and severity of postnatal thyroid hormone deficiency. Endemic cretins with predominant neurological features have had only transient hypothyroidism in the postnatal period, evidenced by their near normal thyroid function and by a lack of hypothyroid clinical features. By contrast, cretins with marked myxedematous features were characterized by permanent and severe postnatal thyroid hormone deficiency. These cretins, in addition to signs of neurological damage, were typically dwarfed, sexually immature, with marked clinical features of myxedema. This second event, influenced by the thyroid gland's morphologic response to its environment (goiter or thyroid atrophy), dictates the final clinical outcome. In conclusion, our hypothesis states that the clinical expression of endemic cretinism is determined by the sum of two pathophysiologic processes. The first process is fetal hypothyroidism which results in the neurological damage of the disorder and the second process is the duration and magnitude of postnatal hypothyroidism which dictates the final clinical appearance.

Clinical picture of endemic cretinism in central Apennines (Montefeltro)

Endemic cretinism is still present in an endemic goiter area of the central Apennines (Montefeltro) (goiter prevalence 55%; mean urinary iodine level 39 micrograms/g creatinine). Clinical and biochemical features of patients with myxedematous, neurologic, and mixed cretinism were studied. Also, in this area, as in most other, neurologic cretinism is more prevalent than myxedematous and mixed forms. The hormonal profiles of the three types of cretinism were clearly different. Nevertheless, all myxedematous cretins had some neurologic disorders (hyperreflexia, increased muscle tone, disorder of gait, Babinski sign, hypoacusia) that were similar to those present in neurologic cretins. These findings suggest that neurologic damage is very similar in all forms of endemic cretinism, reflecting a diffuse insult to the developing fetal nervous system. Furthermore, these data support the hypothesis that the primary pathophysiologic event in the different types of endemic cretinism is represented by maternal and fetal hypothyroidism, while differences may be explained by the extent and duration of postnatal hypothyroidism. All the cretins were over 35 of age, suggesting a severe iodine deficiency in the past decades, and a progressive improvement of nutritional status resulted in "silent iodine prophylaxis." However, recent studies have revealed the persistence of a moderate iodine deficiency, a high prevalence of neurologic hypoacusia, and reduction of mental performance in normal schoolchildren of this area. These findings constitute strong evidence in favor of adequate iodine prophylaxis.

Thyroid atrophy in myxedematous endemic cretinism: possible role for growth-blocking immunoglobulins

We have examined the ability of IgGs obtained from 8 endemic cretins to inhibit TSH-stimulated thyroid cell growth in culture. Clinical and laboratory evidence for hypothyroidism was present in six subjects; the two remaining patients had borderline low serum T4, normal T3 and exaggerated TSH response to TRH. In six patients 2 mg IgG exhibited an inhibitory effect in the cellular growth expressed by a diminished incorporation of 3H-thymidine into the DNA of TSH-stimulated FRTL-5 cells (range: 26-87% inhibition). Seven patients presented clinically with thyroid atrophy of relatively small thyroid enlargements for the degree of chronic iodine deficiency that was present in the area. The remaining subject had a large multinodular goiter and IgG purified from this patient had no inhibitory effect in the FRTL-5 cellular growth. A direct relationship was noted between the degree of thyroid growth inhibition (%) and the basal serum TSH concentration. We conclude that the presence of thyroid growth inhibiting immunoglobulin may be related to the absence of thyroid growth or even thyroid atrophy in endemic cretins.

Endemic cretinism: possible role for thyroid autoimmunity

Thyroid atrophy, rather than goitre, is a characteristic feature of myxoedematous cretinism but its cause and nature are unknown. In this study, purified IgG fractions of serum from patients with myxoedematous endemic cretinism inhibited thyrotropin-induced DNA synthesis in guineapig thyroid segments in a sensitive cytochemical bioassay. IgG from patients with euthyroid neurological endemic cretinism or from normal subjects did not inhibit thyroid growth. Furthermore, in myxoedematous subjects, the presence of the thyroid-growth-blocking immunoglobulins showed a positive relation with thyroid atrophy found on ultrasound. These findings provide a pathogenic basis for the variable clinical expression of endemic cretinism.