Hypothyroidism

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Hypothyroidism Main page
Patient Information
Overview
Classification Primary hypothyroidism Hashimoto's thyroiditis Secondary hypothyroidism Tertiary hypothyroidism
Differentiating different causes of hypothyroidism
Screening
Diagnosis
History and symptoms

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]

Synonyms and keywords: Myxedema; myxoedema; thyroid activity decreased; hypothyroid

Overview

Environmental iodine deficiency is the most common cause of hypothyroidism on a worldwide basis (16). In areas of iodine sufficiency, such as the United States, the most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto’s thyroiditis).Autoimmune thyroid diseases (AITDs) have been estimated to be 5-10 times more common in women than in men.

Classification

The table below presents a classification of isolated thyroid disorders and its causes based on the classification:

		Origin of the defect			Causes
					Endagenous causes	Exagenous causes
		Thyroid	Pituirtary	Hypothalamus		Surgery or radiation	Other causes
Primary hypothyroidism		+	-	-	Congenital hypothyroidism Autoimmune (Hashimoto's) thyroiditis Resistance to TSH	After hyperthyroidism or thyroid cancer treatment: Thyroidectomy Radioiodine therapy Radiation for non-thyroid-related head and neck malignancies including lymphoma	Iodine deficeincy Drug induced thyroiditis Amiodarone Lithium Thionamide Iodine Iterferon Sunitinib Rifampicin Thalidomide Acute infectiuos thyroiditis Trauma-induced
Transient hypothyroidism		+	+	-	Subacute (de Quervain’s) thyroiditis Postpartum thyroiditis	Major surgeries
Central Hypothyroidism	Secondary OR Pituitary originated	-	+	-	Pituitary mass lesions, especially pituitary adenomas Brain cysts and abscesses Meningiomas Dysgerminomas Metastatic tumors Craniopharyngiomas Pituitary apoplexy Sheehan syndrome (postpartum pituitary necrosis) Idiopathic isolated TSH deficiency Lymphocytic or granulomatous hypophysitis	Surgery of pituitary adenomas Radiation therapy Pituitary adenomas Other mass lesions near pituitary gland	Head trauma with injury of the stalk
	Tertiary OR Hypothalamus originated	-	-	+	Hemochromatosis Histiocytosis Autoimmune lymphocytic hypophysitis Developmental abnormalities Internal carotid aneurysms Other central nervous system (CNS) tumors Idiopathic isolated TRH deficiency	Radiation in high doses to: Brain Infratemporal Nasopharyngeal Oropharyngeal	Infections Tuberculosis Syphilis Toxoplasmosis Sarcoidosis

Classification of thyroiditis based on the duration algorythm

History, signs, and symptoms suggestive of hypothyroiditis

Measure FT4 and TSH

Normal FT4, Elevated TSH>5.5

Decresased level of FT4

Subclinical hypothyroidism

Elevated TSH > 5.5

Normal TSH level OR Decreased TSH level < 0.2

Check anti-thyroid antibodies and TPOAb

Check TRH

Increased

Normal

Normal or increased

Decreased

•Autoimmune thyroiditis • Resistance to TSH

•Iodine deficeincy •Thyroiditis

•Pituitary related hypothyroidism

•Hypothalamus related hypothyroidism

Differential diagnosis

Disease		History and symptoms					Laboratory findings							Additional findings
		Fever	Goiter	Pain			TSH	Free T4	T3	T3RU	Thyroglobin	TRH	TPOAb
Primary hypothyroidism	Autoimmune	+	+/- Diffuse	-	+	-	↑	↓	Normal or ↓	Normal	N/↑	Normal	↑	Auto antibodies present (Anti GAD-65 and anti insulin anti bodies)
	Thyroiditis	+		+									Normal
	Others	-	+/-	-
Transient hypothyroidism		+/-	+	+	+	-	↑	↑	Normal	Normal	↑	Normal	Normal	Acanthosis nigricans
Subclinical hypothyroidism		+	+	+	-	+	↑	Normal	Normal	Normal	↑	Normal	Normal or ↑	-
Central Hypothyroidism	Pituitary	+	+	-	-	-	Normal or ↓	Normal or ↓	Normal or ↓	↓	Normal	Normal	Normal	Other hormonal deficiencies
	Hypothalamus	+	+	-	-	-				↑	Normal	↓	Normal	-
Resistance to thyroid hormone		-	-	-	-	-	↑	↑	Normal	Normal	↑	Normal	Normal	In hospitalized patients especially in ICU and CCU
Steroid therapy		+	-	-	-	+	↑	↑	Normal	Normal	↑	↑	N/↑	Acanthosis nigricans,
RTA 1		-	-	-	+	-	Normal	Normal	↑	Normal	↑	Normal	Normal	Hypokalemia, nephrolithiasis
Glucagonoma		-	-	-	-	-	↑	Normal	Normal	Normal	-	Normal	Normal	Necrolytic migratory erythema
Cushing syndrome		-	-	-	-	+	↑	-	Normal	↓	N/↑	↑	Normal	Moon face, obesity, buffalo hump, easy bruisibility

General feature

Symptoms

Symptoms	Constituitional	Local	Reproductive	Neuropsysiological	Others	Physical exam
More common	cold intolerance puffiness decreased sweating coarse skin hypothermia Fever if accompanied by thyroiditis weight gain coarse, brittle, straw like hair with hair loss	obstructive sleep apnea (secondary to macroglossia)	Females can present with galactorrhea and menstrual disturbances	depression	paresthesia and nerve entrapment syndromes	decreased systolic blood pressure increased diastolic blood pressure bradycardia pericardial effusion abdominal distension ascites (uncommon) non-pitting edema (myxedema) pitting edema of lower extremities hyporeflexia with delayed relaxation ataxia
Less common		fullness and pain in the throat and neck	infertility	emotional lability	constipation Pituitary hyperplasia that can lead to hyperprolactinom
		hoarseness sore throat		blurred vision	macroglossia
		goiter		Attention deficit	periorbital puffiness
				slowed speech and movements	Carpal tunnel syndrome

• Metabolic abnormalities associated with hypothyroidism include:
  • anemia,
  • dilutional hyponatremia,
  • hyperlipidemia,
  • reversible increase in creatinine

Complications

Myxedema coma

Rare, severe form of hypothyroidism, a life-threatening condition

• Altered mental status,
• hypothermia,
• bradycardia,
• hypercarbia, and
• hyponatremia.
• Cardiomegaly,
• pericardial effusion,
• cardiogenic shock, and
• ascites
• commonly occurs in individuals with undiagnosed or untreated hypothyroidism who is subjected to an external stress, such as low temperature, infection, or medical intervention (e.g., surgery or hypnotic drugs)