Endocrine System: Thyroglossal Duct Cyst and Thyroid Disorders

Thyroglossal Duct Cyst

• A cystic dilation of a thyroglossal duct remnant
• The thyroid develops at the base of the tongue, then moves down the thyroglossal duct to the anterior neck
• The duct usually disappears, but a persistent duct can form a cyst
• Presents as a neck mass

Hyperthyroidism

• Increased levels of circulating thyroid hormone
• Increased basal metabolic rate (due to increased Na+-K+ ATPase synthesis)
• Increased sympathetic nervous system activity (due to increased B₁-adrenergic receptor expression)
• Clinical features include weight loss despite increased appetite, heat intolerance and sweating, tachycardia with increased cardiac output, arrhythmia, tremor, anxiety, insomnia, heightened emotions, staring gaze with lid lag, diarrhea, oligomenorrhea, bone resorption with hypercalcemia (risk for osteoporosis), decreased muscle mass with weakness, hypocholesterolemia, and hyperglycemia

Graves' Disease

• An autoimmune disease (IgG stimulates TSH receptor)
• Leads to increased thyroid hormone synthesis and release
• Most common cause of hyperthyroidism
• Commonly affects women of childbearing age (20-40 years)
• Clinical features include hyperthyroidism, diffuse goiter, exophthalmos, and pretibial myxedema

Lingual Thyroid

• Persistence of thyroid tissue at the base of the tongue
• Presents as a base of tongue mass

Multinodular Goiter

• Enlarged thyroid gland with multiple nodules
• Due to relative iodine deficiency
• Usually nontoxic (euthyroid)
• Rarely, regions become independent of TSH, leading to T4 release and hyperthyroidism (toxic goiter)

Hypothyroidism: Cretinism

• Hypothyroidism in newborns and infants
• Characterized by mental retardation, short stature, skeletal abnormalities, coarse facial features, enlarged tongue, umbilical hernia
• Thyroid hormone is essential for brain and skeletal development
• Causes include maternal hypothyroidism during pregnancy, thyroid agenesis, dyshormonogenetic goiter, and iodine deficiency

Hypothyroidism: Myxedema

• Hypothyroidism in older children or adults
• Clinical features include decreased basal metabolic rate, decreased sympathetic nervous system activity, myxedema (accumulation of glycosaminoglycans in skin and soft tissue), weight gain despite normal appetite, slowed mental activity, muscle weakness, cold intolerance, bradycardia, decreased cardiac output (leading to shortness of breath and fatigue), oligomenorrhea, and hypercholesterolemia

Hashimoto's Thyroiditis

• Autoimmune destruction of the thyroid gland
• Most common cause of hypothyroidism in areas with adequate iodine
• Initially presents with hyperthyroidism then progresses to hypothyroidism
• Antithyroglobulin and antithyroid peroxidase antibodies are often present
• Chronic inflammation, germinal centers, and Hurthle cells (eosinophilic metaplasia) seen on histology
• Increased risk for B-cell lymphoma

Subacute Granulomatous (De Quervain) Thyroiditis

• Granulomatous thyroiditis following viral infection
• Presents as a tender, enlarged thyroid with transient hyperthyroidism
• Usually self-limited; rarely progresses to hypothyroidism

Riedel Fibrosing Thyroiditis

• Chronic inflammation resulting in extensive thyroid fibrosis
• Presents as hypothyroidism with a hard, nontender thyroid
• Fibrosis may involve surrounding structures
• Usually not malignant, but can mimic anaplastic carcinoma

Thyroid Neoplasia

• Thyroid nodules are often benign
• Radioactive iodine uptake studies help differentiate benign and malignant nodules
• Increased uptake suggests Graves' or nodular goiter
• Decreased uptake suggests adenoma or carcinoma, requiring biopsy
• Fine-needle aspiration (FNA) is used for biopsy

Papillary Carcinoma

• Most common thyroid cancer (80%)
• Exposure to ionizing radiation is a risk factor
• Papillae, clear "Orphan Annie" nuclei, and nuclear grooves
• Often spreads to cervical lymph nodes but has good prognosis (10-year survival >95%)

Follicular Carcinoma

• Malignant proliferation of follicles
• Invasion of the capsule helps distinguish it from follicular adenoma
• Entire capsule must be examined microscopically
• Metastasis usually occurs hematogenously

Medullary Carcinoma

• Malignant proliferation of parafollicular C cells, comprising 5% of thyroid cancers
• C cells produce calcitonin
• High levels of calcitonin can lead to hypocalcemia; detected by biopsy
• Familial cases frequently associated with MEN 2A or 2B (mutations in RET oncogene)

Anaplastic Carcinoma

• Undifferentiated malignant thyroid cancer
• Usually arises in elderly patients
• Locally invasive, often causing dysphagia or respiratory problems
• Poor prognosis

This quiz covers key concepts related to the thyroglossal duct cyst, hyperthyroidism, and Graves' Disease. Understand the development and implications of these conditions, their clinical features, and effects on the body. Test your knowledge on the endocrine system's complexities and related disorders.