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 Interferon 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 to: Pituitary adenomas Other mass lesions near pituitary gland	Head trauma with injury of the stalk
	Tertiary OR Hypothalamus originated	-	-	+	Hemochromatosis Histiocytosis 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 hypothyroidism

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 autoantibodies 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	↑	May be accompanied by other autoimmune diseases
	Thyroiditis	+	+/-	+	↑	↓	Normal	Normal		Normal	Normal
	Others	-	+/-	-	↑	↓	Normal	Normal		Normal	Normal
Transient hypothyroidism		+/-	+	+	↑	↑	Normal	Normal	↑	Normal	Normal
Subclinical hypothyroidism		+	+	+	↑	Normal	Normal	Normal	↑	Normal	Normal or ↑
Central Hypothyroidism	Pituitary	+	+	-	Normal or ↓	Normal or ↓	Normal or ↓	↓	Normal	Normal	Normal
	Hypothalamus	+	+	-				↑	Normal	↓	Normal
Resistance to TSH/TRH		-	-	-	↑	Normal or ↓	Normal or ↓	Normal	Normal	↑/↓	Normal

General feature

Symptoms

Symptoms	Constituitional	HEENT	Neuromuscular	Others	Complications
More common	Cold intolerance Decreased sweating Hypothermia Weight gain	Hoarseness Goiter Fullness in the throat and neck	Depression Emotional lability Attention deficit	Constipation	Macroglossia Obstructive sleep apnea Paresthesia Nerve entrapment syndromes (carpal tunnel syndrome) Blurred vision (central hypothyroidism)
Less common	Puffiness coarse skin coarse, brittle, straw like hair with hair loss Fever if accompanied by thyroiditis	Sore throat Periorbital puffiness	Slowed speech and movements		Pituitary hyperplasia followed by hyperprolactinoma Ataxia Myxedema coma (with non-pitting edema) Cardiomegaly Pericardial effusion Ascites hyperlipidemia Galactorrhea Infertility

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