Cretinism and Juvenile Hypothyroidism
Essentials of Diagnosis
Dwarfism, mental retardation, dry, yellow, cold skin, "pot belly" with umbilical hernia. PBI and T4 low; serum cholesterol elevated. Delayed bone age; "stippling" of epiphyses.
The causes of cretinism and juvenile hypothyroidism are as follows (after Wilkins):
A. Congenital (Cretinism):
- Thyroid gland absent or rudimentary (embryonic defect; most cases of sporadic cretinism).
- Thyroid gland present but defective in hormone secretion; goitrous or secondarily atrophied. Due to extrinsic factor (deficient iodine, goitrogenic substances; most cases of endemic cretinism); or due to maternal factors (some cases of congenital goiter). Many cases are familial.
B. Acquired (Juvenile Hypothyroidism):
Atrophy of the gland or defective function may be due to unknown causes, thyroiditis, or operative removal (lingual thyroid or toxic goiter), or secondary to pituitary deficiency.
A. Symptoms and Signs :
All degrees of dwarfism may be seen, with delayed skeletal maturation, apathy, physical and mental torpor, dry skin with coarse, dry, brittle hair, constipation, slow teething, poor appetite, large tongue, "pot belly" with umbilical hernia, deep voice, cold extremities and cold sensitivity, and true myxedema of subcutaneous and other tissues. A yellow, carotenemic skin is not infrequent. The thyroid gland is usually not palpable, but a large goiter may be present which may be diffuse or nodular. Sexual development is retarded but maturation eventually occurs. Menometrorrhagia or amenorrhea may be seen in older girls. Rarely, sexual precocity and galactorrhea with pituitary enlargement may occur. Deafness is occasionally associated with goiters. Nephrocalcinosis is a rare finding in cretinism.
B. Laboratory Findings :
The BMR is probably the least reliable (especially in infants and children) and the T4 (D) the most reliable index of thyroid activity; the latter is usually under 3 mg/100 ml. Serum cholesterol is frequently elevated. Radioactive iodine uptake is very low in athyroid individuals, but it may be high in goitrous cretins although the iodine is not bound in the gland and is released. By special technics, abnormal circulating iodine compounds and enzymatic defects in thyroid hormone production and release are demonstrable in some patients. Others show circulating autoantibodies to thyroid constituents. TSH by radioimmunoassay is invariably elevated.
C. X-Ray Findings :
Delayed skeletal maturation is a constant finding, often with "stippling" of the epiphyses (especially of the femoral head), with flattening; widening of the cortices of the long bones, absence of the cranial sinuses, and delayed dentition may also be noted.
It is of practical interest to differentiate primary hypothyroidism from pituitary failure because in the latter instance a search for a pituitary lesion must be undertaken. Treatment with thyroid hormone must be instituted cautiously when hypothyroidism is secondary to pituitary failure since it may occasionally precipitate adrenal crisis. Radioiodine uptake studies before and after exogenous TSH administration will often show whether a gland is present or not. TSH assay (when available) generally will help greatly in the differentiation of primary hypothyroidism from pituitary hypothyroidism. True myxedema and hyper-cholesterolemia are less common with hypopituitarism. Cretinism is most often confused with Down's syndrome, although retarded skeletal development is rare in mongoloid infants. Macroglossia may be due to tumor; eg, lymphangioma. The dry skin of ichthyosis may be misleading. All causes of stunted growth and skeletal development must be considered as well. Rather than risk the development of full-blown cretinism in the questionable case, a trial of thyroid therapy is reasonable.
A. Specific Therapy :
Thyroid or a synthetic preparation is used. The initial dosage varies with the severity of the hypothyroidism.
- Caution- When treating patients with severe myxedema or myxedema heart disease, or elderly patients with hypothyroidism with other associated heart disease, begin with small doses of thyroid, 8-15 mg daily for 1 week, and increase the dose every week by 15 mg daily up to a total of 100-200 mg daily. This dosage should be continued until signs of hypothyroidism have vanished or mild toxic symptoms appear, and the dosage then stabilized to maintain the T, at normal levels. An alternative method is the use of small amounts of sodium liothyronine, eg, 5 mg initially with gradual increase to tolerance.
- Patients with early hypothyroidism may be started with larger doses, 30 mg daily, increasing by 30 mg every week to the limit of tolerance.
- Maintenance- Each patient's dose must be adjusted to obtain the optimal effect. Most patients require 120-180 mg daily for maintenance. Optimal dosage can be estimated by following the PBI or T4, but clinical judgment is often the best guide.
- Levothyroxine sodium (Synthroid, Letter), 0.15-0.3 mg/day, is as good as thyroid. Its action is more predictable than that of crude thyroid. If thyroxine is used, the T4 should be raised to the high normal level.
- When a rapid response is necessary, sodium liothyronine (T3, Cytomel) may be employed. Begin with very low doses because of its speed of action. Begin with 5mg and increase slowly. Note: The T4 cannot be used as a guide to T3 therapy.
- Mixtures of T4 and T3 in a ratio of 4:1 -liotrix (Euthroid(D, Thyrolar) - have been recently introduced as complete replacement therapy.
- Sodium dextrothyroxine (Choloxin) may be used in cardiac hypothyroid patients who cannot tolerate other thyroid medications, but its value and safety have been questioned recently.
- Myxedema coma is a medical emergency with a high mortality rate. Triiodothyronine, 10-25 mg or more given by stomach tube every 8 hours, or, preferably, levothyroxine sodium (Synthroid), 200-400 mg IV as a single injection and repeated once in a dose of 100-200 mg in 12 hours, with the addition of hydrocortisone, 100 mg every 8 hours, may be life-saving. The patient must not be warmed, and adequate pulmonary ventilation must be provided.
- Suppression of serum TSH will become a useful test of adequate maintenance or replacement therapy in hypothyroidism.
B. Needless Use of Thyroid:
- Questionable diagnosis- If a patient can tolerate above 200 mg daily of thyroid, the diagnosis of hypothyroidism should be questioned even though some hypothyroid patients require this or larger amounts.
Normal individuals and obese and other non-hypothyroid individuals can often tolerate doses up to 300-500 mg daily without change, development of toxic symptoms. "Metabolic insufficiency" is a questionable entity. The empiric use of thyroid in cases of amenorrhea or infertility warrants further consideration.
The progress and outcome of the disease depend largely upon the duration of thyroid deficiency and the adequacy and persistence of treatment. Since mental development is at stake, it is of utmost importance to start treatment early. The prognosis for full mental and physical maturation is much better if the onset is later in life. Congenital cretins almost never attain full mental development. Skeletal and sexual maturation, though often retarded, do take place normally under continued thyroid therapy. By and large, the response to thyroid therapy is gratifying but therapy usually must be maintained throughout life.
Marcus A. Krupp Md
The author is Clinical Professor of Medicine Stamford University School of Medicine, USA.
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