Thyroid Disorders

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Development: The thyroid gland develops from the floor of the oral cavity, specifically from an area known as the foramen cecum. It begins its descent to its final position in the neck by the end of the first trimester.
Activation of Axis: By the second trimester, the hypothalamic-pituitary-thyroid (HYP-PIT-THYROID) axis becomes active, leading to the regulation of thyroid hormone production.
Hormone Metabolism: Peripheral metabolism of thyroid hormones (conversion of T4 to T3) begins in the third trimester.
Placental Transfer: Thyroid hormones (T3, T4, and TSH) do not significantly cross the placenta. However, thyroid antibodies (e.g., TSH receptor antibodies) and anti-thyroid drugs (e.g., propylthiouracil, methimazole) can cross the placenta and affect fetal thyroid function.

Hypothalamus: Secretes thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland.
Pituitary Gland: Produces thyroid-stimulating hormone (TSH), which acts on the thyroid gland to promote the synthesis and release of thyroid hormones.
Thyroid Gland:
- Produces triiodothyronine (T3) and thyroxine (T4) through the iodination of tyrosine.
- T3 is more potent than T4. Most T3 is produced by the peripheral deiodination of T4.
Negative Feedback: Thyroid hormones exert a negative feedback effect on both the hypothalamus and pituitary gland, regulating their secretion of TRH and TSH, respectively.

Increase O₂ Consumption: Enhances basal metabolic rate.
Increase Protein Synthesis: Supports growth and tissue repair.
Stimulate Growth & Differentiation: Important for linear growth and brain maturation.
Influence Metabolism: Affects carbohydrate, lipid, and vitamin metabolism.

Definition: A condition characterized by inadequate production of thyroid hormones.
Types:
- Congenital Hypothyroidism: Present at birth.
- Acquired Hypothyroidism: Develops later in life.
- Can be goitrous (enlarged thyroid) or non-goitrous.

Incidence: Occurs in approximately 1 in 4,000 births.
Presentation: May show delayed development of physical and mental functions.
Causes:
- Thyroid Agenesis: Absence of the thyroid gland.
- Thyroid Aplasia: Underdeveloped thyroid gland.
- Ectopic Thyroid Tissue: Abnormal location of the thyroid gland.
- Inborn Errors of Metabolism: Defects in the thyroid hormone synthesis pathway, often leading to a goitrous form.

Birth and Early Signs:
- Post-term delivery
- Macrosomia (large body size)
- Subtle initial symptoms
Early Symptoms:
- Hypothermia
- Abdominal distension
- Respiratory distress
- Large fontanelle
- Lethargy
- Poor feeding
- Prolonged jaundice
- Umbilical hernia
- Mottled skin
- Large tongue (macroglossia)
- Coarse facial features
- Constipation
- Hoarse cry
Developmental Delays:
- Delayed developmental milestones
- Mental retardation
- Delayed bone age

Diagnosis:
- Newborn Screening: Essential for early detection.
- Laboratory Tests: Measure serum T4 and TSH levels.
Treatment:
- Thyroxine Replacement: Administered to prevent mental retardation.
- Timing: Treatment should start within the first 2 weeks of life for optimal outcomes.

Causes:
- Chronic Lymphocytic Thyroiditis (Hashimoto Thyroiditis): Most common cause (incidence 1:1,250).
- Iodine Deficiency: Rare in modern contexts.
- Iatrogenic: Due to treatment for hyperthyroidism.
- Drug-Induced: Ingestion of iodide-containing drugs (e.g., amiodarone).

Epidemiology:
- Female:Male ratio = 4-7:1
- Common in adolescents but can occur as early as the first year of life.
Pathophysiology:
- An autoimmune disorder often associated with other autoimmune conditions (e.g., Type 1 Diabetes Mellitus).
- Characterized by lymphocytic infiltration of the thyroid gland with hyperplasia leading to goitre.
- Can present with hyperthyroidism, euthyroidism, or hypothyroidism.

Common Symptoms:
- Goitre
- Short Stature
- Vitiligo
- Cold, Clammy Skin
- Cold Intolerance
- Pallor
- Bradycardia
- Physical and Mental Lethargy
- Hypotonia
- Muscle Weakness
- Delayed Bone Age
- Menstrual Irregularities
- Pleural and Pericardial Effusion

Diagnosis:
- Thyroid function tests: T3, T4, TSH
- Thyroid Ultrasound
- Anti-Thyroid Antibodies
Treatment:
- Thyroxine replacement therapy.

Graves' Disease: The most common cause, an autoimmune disorder resulting in the overproduction of thyroid hormones.
McCune-Albright Syndrome: A genetic disorder that can cause autonomous thyroid hormone production.
Thyroid Carcinoma: Malignant tumors of the thyroid gland that may produce thyroid hormones.
Subacute Thyroiditis: Inflammation of the thyroid, often following a viral infection, leading to transient hyperthyroidism.
Acute Thyroiditis: Bacterial or other infectious inflammation causing an overproduction of thyroid hormones.
Iatrogenic: Due to excessive administration of thyroid hormone medications.

Incidence: 1 in 5,000
Female to Male Ratio: 5:1
Peak Age: 11–15 years
Pathophysiology: Autoimmune disorder involving stimulating auto-antibodies, resulting in increased levels of T3 and T4 and decreased TSH.

Goitre
Restlessness
Eye Signs: Lid lag, exophthalmos
Cardiovascular: Tachycardia, palpitations, hypertension, arrhythmias, tremors
Increased Sweating
Heat Intolerance
Fatigue
Weight Loss
Diarrhea
Myopathy

Laboratory Findings:
- Elevated T3 and T4
- Decreased TSH
- Presence of Thyroid Peroxidase Antibodies and Anti-TRAB

Medical:
- Propranolol: To manage cardiovascular symptoms.
- Methimazole or Carbimazole: Antithyroid drugs to reduce hormone production.
- Propylthiouracil (PTU): Another antithyroid medication option.
Surgical:
- Thyroidectomy: Partial or total removal of the thyroid gland.
Radioactive Iodine Therapy:
- Use of radio-iodide to destroy overactive thyroid tissue.