Hypothyroidism

HYPOTHYROIDISM 73A

A 55-year-old woman complains of fatigue, 30 lb of weight gain despite dieting, constipation, thinning hair, and menorrhagia. On physical examination, the thyroid gland is not palpable; the skin is cool, dry, and rough; the heart sounds are quiet; the pulse rate is 50 beats/min; and the deep tendon reflexes show delayed relaxation. The rectal and pelvic examinations are normal, and the stool is guaiac negative.

What are the salient features of this patient’s problem? How do you think through her problem?

Salient features: Middle-aged woman; weight gain; constipation; menorrhagia; thinning hair; dry skin; bradycardia; delayed relaxation of reflexes

How to think through: What major disease categories might present with fatigue and weight gain? (Depression, Cushing syndrome, hypothyroidism.) In addition to the fatigue, constipation, weight gain, alopecia, and menorrhagia, what other symptoms should be sought in this case? (Cold intolerance, mental clouding, muscle weakness, or cramping.)

What are common causes of hypothyroidism? (Autoimmune [Hashimoto] thyroiditis is most common; drug toxicity, including amiodarone and lithium; iodine deficiency; surgical resection or radioablation of the thyroid gland.) If the thyroid-stimulating hormone [TSH] value in this case proves to be low normal, what diagnosis should we consider? (Secondary hypothyroidism caused by a pituitary process such as a mass effect from a prolactin-producing pituitary tumor.) Is this patient at risk for autoimmune hypothyroidism? (Yes, given her age and sex.) How should she be evaluated? (A serum TSH alone is the appropriate initial test; an abnormal TSH level should be followed by a free thyroxine (T₄). Tests for thyroperoxidase and thyroglobulin antibodies are positive in most cases of autoimmune thyroiditis but are nonspecific and may be positive in the setting of acute illness.) If this patient’s TSH value is elevated, and her free T₄ is low, how should thyroid replacement therapy be initiated? (Start low; go slow. The primary concern is that coronary artery disease can be “unmasked” if the metabolic rate accelerates too quickly.) What are other risks of overtreatment? (Osteoporosis, atrial fibrillation.)

HYPOTHYROIDISM 73B

What are the essentials of diagnosis and general considerations regarding hypothyroidism?

Essentials of Diagnosis

Weakness, cold intolerance, constipation, depression, menorrhagia, hoarseness

Dry skin, bradycardia, delayed return of deep tendon reflexes

TSH is elevated and free thyroxine (FT₄) low

General Considerations

Primary hypothyroidism is caused by thyroid gland disease, and secondary hypothyroidism is caused by a lack of pituitary TSH; TSH may be mildly elevated in euthyroid individuals.