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

Thyroxine (T4) and triiodothyronine (T3) are produced from the thyroid gland. Thyroid hormones are important in regulating different body functions, and their deficiencies are associated with different symptoms including the decrease in energy metabolism, decreased appetite, cold intolerance, and slightly low basal body temperature (low basal metabolic rate). Iodine deficiency is recognized as the most common cause of hypothyroidism world widely. In developed countries and areas of iodine sufficiency, the most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto’s thyroiditis) with a more prevalence in women than men. Symptom and signs of hypothyroidism is mostly related to the magnitude of the thyroid hormone deficiency, and the acuteness with which the deficiency develops rather than the cause of hypothyroidism. However, the typical clinical manifestations of hypothyroidism may vary depending on the origin of the disease. Clinical scenario- if associated with secondary and tertiary hypothyroidism, may present other coexisting endocrine deficiencies such as hypogonadism and adrenal insufficiency, that may mask the manifestations of hypothyroidism. Although hypothyroidism diagnosis is mainly a laboratory diagnosis, the coexisting conditions and wide variation in clinical presentation may make the diagnosis hard. Subclinical hypothyroidism on the other hand is mostly asymptomatic, but may be transformed to clinical. Recent researches have shown subclinical hypothyroidism may have various consequences, such as hyperlipidemia and increased risk for the development of cardiovascular disease, even heart failure, somatic and neuromuscular symptoms, infertility and other complications.2895281

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	-	↑	↓	N/↓	Normal	N/↑	Normal	↑	May be accompanied by other autoimmune diseases
	Thyroiditis	+	+/-	+	↑	↓	Normal	Normal	N/↑	Normal	Normal	Infectious thyroiditis associated with neck pain
	Others	-	+/-	-	↑	↓	Normal	Normal	N/↑	Normal	Normal	History of hyperthyroiditis Drug history
Transient hypothyroidism		+/-	-	+/-	↑	↑	Normal	Normal	↑	Normal	Normal	May present primarily with hyperthyroiditis
Subclinical hypothyroidism		-	-	-	↑	Normal	Normal	Normal	↑	Normal	N/↑	Asymptomatic
Central Hypothyroidism	Pituitary	+	-	-	N/↓	N/↓	N/↓	↓	Normal	Normal	Normal	Other pituitary hormone deficiencies signs
	Hypothalamus	+	-	-				↑	Normal	↓	Normal	Other pituitary hormone deficiency signs
Resistance to TSH/TRH		-	-	-	↑	N/↓	N/↓	Normal	Normal	↑/↓	Normal	Rare

History and symptoms

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