• Hypothyroidism is a clinical syndrome caused by insufficient circulating levels of thyroid hormones below that required to meet physiologic demands. Multiple etiologies can lead to hyperthyroidism the most important are thyroiditis, endemic goiter, and iatrogenic destruction of the thyroid gland as treatment for hyperthyroidism. As discussed in Thyroid Hormone Physiology thyroid hormones play dual roles in development as well as maintaining sufficient whole-body metabolism. Consequently, insufficiency of thyroid hormones typically results in distinct clinical syndromes in adults and children.
Clinical Syndrome in Adults
  • Given the diverse physiological roles of thyroid hormones in adults the clinical consequences of thyroid hormone deficiency are equally varied. Decreased whole-body metabolism results in a reduced basal metabolic rate leading to weight gain. Furthermore, decreased body temperature can manifest as an intolerance to cold environmental temperatures. The heart may display bradycardia due to deficient sympathetic stimulation.
  • CNS effects include mental slowing, lethargy, and listlessness. Skin of patients with hypothyroidism is typically dry and hair loss manifests from brittling of hair. Reduced GI Motility may lead to constipation.
  • For a complex reason, deficiency in thyroid hormones causes deposition of mucopolysaccharides in a variety of connective tissues. Mucopolysaccharides are long chains of sugar residues which retain water and thus form a gel-like material. Clinically apparent deposition of mucopolysaccharides occurs in the skin and vocal cords. Deposition in dermis results in a condition known as Myxedema which looks like generalized edema but does not pit (hence a non-pitting edema). Deposition in the vocal cords can cause hoarseness.
  • Certain etiologies may result in goiter of the neck although the pathogenesis of this is etiology-specific
Clinical Syndrome in Children
  • The following clinical syndrome, historically termed Cretinism, develops if hypothyroidism is encountered in fetuses or neonates. Childhood hypothyroidism is characterized by reduced stature as well as mental retardation.
  • Lifettime supplementation with levothyroxine (T4).