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Endocrinology and Metabolism Hypothyroidism Diagnosis Symptoms and Signs Look for symptoms suggesting hypothyroidism: . weakness, Ietharry, fatigue . depression, impaired concentration . myalgia . cold intolerance o constipation . weight gain r menstrual irregularity or menorrhagia . carpal tunnel syndrome ' Look for signs suggesting hypothyroidism: . bradycardia ' hlpothermia r goiter o cool dry skin . delayed deep tendon reflex relaxation phase o myopathy Causes The most common causes of hypothyroidism include . chronic lymphocytic (Hashimoto) thyroiditis o thyroidectomy o previous radioactive iodine ablation o history of external beam radiation to the neck Transient mild hlpothyroidism typically occurs during the second phase of destructive thyroiditis (initial phase is hyperthy- roidism). Permanent hypothyroidism may follow either postpartum thyroiditis (more common) or zubacute thyroiditis (less common). Medication-induced hypothyroidism can occur with the use of certain drugs, including lithium carbonate, interferon alfa, interleukin 2, and amiodarone. Central hypothyroidism results from pituitary disease or from previous surgery or radiation therapy to the sella. TSH and free To are suppressed. Testing Order TSH and free To to make the diagnosis. Measurement of T, levels is generally not necessary. An antithyroid peroxidase antibody assay is associated with Hashimoto thyroiditis but is not needed to make the diagnosis; high levels are associated with an increased risk of permanent hypothyroidism. Hypothyroidism may be associated with hyperprolactinemia; hyponatremia; and increased CK, AST, and cholesterol levels. 61