Acquired Hypothyroidism

Katrina L. Parker, MD

Acquired Hypothyroidism

• The thyroid gland makes too little or no thyroid hormone

• Occurs anytime during childhood• Usually affects infants starting at 6 months of

age

Historical Review

• 1912 Dr. Hakaru Hashimoto described 4 patients with a chronic disorder of the thyroid

• He termed it struma lymphomatosa• The thyroid glands had– Fibrosis– Diffuse lymphocytic infiltation– Parenchymal atrophy– Eosinophilic changes

Etiology

• Autoimmune disease• Delayed onset congenital hypothyroidism• Iodine deficiency• Medications – Anti depressants– Lithium– Amiodarone - 1 4-18% of patients

• Radiation therapy • Radioactive iodine therapy • Thyroid surgery

Causes of Acquired Hypothyroidism• Thyroidectomy or radioiodine therapy– Thyroid cancer– Thyroxicosis– Lingual thyroid– Isolated midline thyroid

• TRH deficiency• Pituitary disorder• Chronic infections• Idiopathic

Etiology

• Environmental factors– High iodine intake– Selenium deficiency– Pollutants – tobacco smoke– Infectious disease- chronic hepatits C

Incidence

• 0.3 to 1.5 cases per 1000 population per year• 15-20 times more frequent in women than men• in families with hypothyroidism or autoimmune

disease• Associated with other autoimmune diseases – Type 1 DM– Celiac disease– Type 2 and Type 3 polyglandular autoimmune

disorders

Prevalence

• Annual incidence 4 per 100 women and 1 per 1000 men

• More common in certain populations• sporadic inheritance, sometimes autosomal

recessive• post-partum thyroiditis affects 5% of women

Absorption of thyroid hormone

• Affected by – Iron supplements– Questran– Antacids containing Aluminum hydroxides– Calcium supplements– Soy products– Rifampin– Anti convulsants

Hypothyroidism Classification TYPE Origin Description

Primary Thyroid gland The most common form is Hashimoto thyroiditis

Secondary Pituitary Gland Occurs if the pituitary does not create enough TSH

Tertiary Hypothalamus The hypothalamus fails to produce sufficient TRH

Hypothyroidism and Concurrent Conditions

• Depression• Euthyroid sick syndrome– Starvation– Critically ill – Corticosteroids and dopamine

• Infertility

Differential Diagnosis

• Primary versus hypothalamic failure• Short stature– Coarse features R/O• Down Syndrome• Hurler & Hunter Syndrome• Generalized gangliosidosis

Presentation of Hashimoto’s Thyroiditis

• Euthyroidism and goiter• Subclinical hypothyroidism and goiter• Primary thyroid failure• Adolescent goiter• Painless thyroiditis or silent thyroiditis• Postpartum painless thyrotoxicosis• Alternating hypo- and hyperthyroidism

Signs• Depression• Physical & mental sluggishness• Dry skin• Constipation• Weight gain with poor appetite• Dyspnea• Poor muscle tone• Menorrhagia• Diminished sweating• Hoarse voice or cry/large tongue

Signs

• Coarse, dry skin• Cool peripheral extremities• Puffy face, hands and feet (myxedema)• Bradycardia• Peripheral edema• Delayed tendon reflex relaxation • Carpal tunnel syndrome• Mild unexplained weight gain NOT morbid obesity

• Skin – dry, thick, scaly, coarse• Hair- brittle, dry, coarse, excessive• Lateral thinning of the eyebrows• Prominent axillary & supraclavicular fat pads in

infants• Growth changes – short stature, infantile skeletal

proportions with relatively short extremities• Infantile naso-orbital configuration• Delayed epiphyseal development

• Delayed closure of fontanelles• Delayed dental eruption• Delayed epiphyseal development• Menometrorrhagia or galactorrhea

Labs

• Decreased TT4 and FT4, elevated TSH• Thyroid antibodies – Anti- Thyroglobulin and anti thyroid perioxidase (TPO)

• R/O TBG deficiency• Normocytic anemia• Elevated cholesterol and carotene in childhood

but normal or low in infants• Decreased GH levels

Imaging

• Skeletal maturation is delayed• Ossification centers of the hip – Single stippled– Multiple small areas

• Anterior beaking of the vertebrae• Coxa vara & coxa plana• Thyroid scan or ultrasound

Treatment

• Levothyroxine– The drug of choice– Dosage infants 10-12 mg/kg/day

• Long standing hypothyroidism start with a low dose of 25-50 ug daily and gradually increase

• Monitor TSH and FreeT4

Treatment

• T4 only– Currently the standard treatment– Involves supplementation of levothyroxine alone

• T4 and T3 in combination– Involves administering both synthetic L-T4 and L-T3

simultaneously in combination• Desiccated Thyroid Extract– animal based thyroid extract– contains natural forms of l-t4 and l-t3e

Glandular Concentrates

• Sold in health food stores• Are not regulated by the FDA• Potency is not guaranteed

QUESTIONS