![]() ![]() Lipid profile: ↑ low-density lipoproteins, ↑ triglycerides.Skin and appendages: skin dryness, alopecia.Generalized decrease in the basal metabolic rate → decreased oxygen and substrate consumption, leading to:.Tertiary hypothyroidism: hypothalamic disorders → ↓ TRH levels → ↓ TSH levels → ↓ T 3/T 4 levels.Secondary hypothyroidism : pituitary disorders → ↓ TSH levels → ↓ T 3/T 4 levels.Primary hypothyroidism : peripheral ( thyroid ) disorders → T 3/T 4 are not produced ( ↓ levels) → compensatory ↑ TSH.The hypothalamus, anterior pituitary gland, and thyroid gland, together with their respective hormones, comprise a self-regulatory circuit referred to as the “ Hypothalamic-pituitary-thyroid axis.” Multinucleated giant cells and granuloma formation.Lymphocytic infiltration with germinal centers and oncocytic- metaplastic cells ( Hurthle cells).Late-stage: normal-sized or small if extensive fibrosis has occurred.Early-stage: rubbery and symmetrically enlarged.Very few patients present with hyperthyroidism.Most patients without hypothyroidism remain euthyroid.Transient hyperthyroidism → hypothyroidism.Classic triphasic course: hyperthyroid → hypothyroid → recovery.In the late phase, hypothyroidism manifests. Hashitoxicosis: in the early phase, thyroid hormone is released from damaged thyroid cells, causing transient hyperthyroidism.Asymptomatic or transient hyperthyroidism → hypothyroidism.Iodine deficiency (most common cause worldwide).Thyroid dysgenesis (most common cause in iodine sufficient regions).Viral and mycobacterial infections causing damage to follicular cells.Variant of subacute lymphocytic thyroiditis.Within 1 year of delivery in 5:100 of women.Most common cause of hypothyroidism in the US.Subacute granulomatous thyroiditis (De Quervain) Overview of common causes of primary hypothyroidism Tertiary hypothyroidism: hypothalamic disorders → TRH deficiency.Secondary hypothyroidism: pituitary disorders (e.g., pituitary adenoma) → TSH deficiency.Thyroid dysplasia: a disorder of embryologic development characterized by abnormal development and/or location of thyroid tissue (e.g., lingual thyroid).Riedel thyroiditis : occurs in IgG 4-related systemic disease.Nutritional (insufficient intake of iodine): the most common cause of hypothyroidism worldwide, particularly in iodine-deficient regions.Iatrogenic: e.g., post thyroidectomy, radioiodine therapy, antithyroid medication (e.g., amiodarone, lithium).De Quervain thyroiditis ( subacute granulomatous thyroiditis) : often subsequent to a flu-like illness.Postpartum thyroiditis ( subacute lymphocytic thyroiditis).Associated with HLA-DR3 and other autoimmune diseases (e.g., vitiligo, pernicious anemia, type 1 diabetes mellitus, and systemic lupus erythematosus ).The most common cause of hypothyroidism in iodine-sufficient regions. ![]() Primary hypothyroidism: insufficient thyroid hormone production.Therapy for both acquired and congenital hypothyroidism consists of lifelong treatment with levothyroxine and regular checkups to monitor disease activity. Accordingly, neonatal screening for hypothyroidism 24–48 hours after birth is required by law in most states. Children with congenital hypothyroidism often have umbilical hernias and, without early treatment, can develop severe developmental delay. In adults, the diagnosis is established based on serum thyroid-stimulating hormone ( TSH) and free T 4 levels (FT 4). More severe manifestations include myxedematous heart disease and myxedema coma, which may be fatal if left untreated. Typical clinical features include fatigue, cold intolerance, dry skin, and constipation. The pathophysiology of hypothyroidism is characterized mainly by a reduction of the basal metabolic rate and generalized myxedema. The etiology of acquired hypothyroidism is typically autoimmune ( Hashimoto thyroiditis) or iatrogenic. Congenital hypothyroidism is usually caused by thyroid dysplasia or aplasia. Hypothyroidism may be congenital or acquired. In very rare cases, hormone production may be sufficient, but thyroid hormones may have insufficient peripheral effects. Hypothyroidism is a condition in which the thyroid gland is underactive, resulting in a deficiency of the thyroid hormones triiodothyronine (T 3) and thyroxine (T 4). ![]()
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