A.8 Hypothyroidism Flashcards
A.8 Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland is underactive, resulting in a deficiency of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). In very rare cases, hormone production may be sufficient, but thyroid hormones may have insufficient peripheral effects. Hypothyroidism may be congenital or acquired.
A.8 Hypothyroidism
Epidemiology
Approximately 1 in 2,000 individuals globally are affected by congenital hypothyroidism.
More prevalent in women (1 per 11,000) compared to men (1 per 41,000).
A.8 Hypothyroidism
Congenital Hypothyroidism:
Congenital hypothyroidism is usually caused by thyroid dysplasia or aplasia.
- Sporadic Cases: (~85% of cases)
- Genetic Factors: Hereditary forms of hypothyroidism.
A.8 Hypothyroidism
Acquired Hypothyroidism:
Primary Hypothyroidism: Caused by insufficient thyroid hormone production.
Hashimoto’s Thyroiditis
Postpartum Thyroiditis
Iatrogenic Causes: Due to medical treatments (e.g., thyroidectomy, radiation).
Nutritional Deficiencies: Such as iodine deficiency.
Autoimmune Conditions: Resulting in IgG4-related thyroiditis.
Secondary Hypothyroidism: Disorders affecting the pituitary gland leading to TSH deficiency.
Tertiary Hypothyroidism: Disorders affecting the hypothalamus and TSH levels.
The etiology of acquired hypothyroidism is typically autoimmune (Hashimoto thyroiditis) or iatrogenic.
A.8 Hypothyroidism
Pathophysiology
Primary Hypothyroidism:
Peripheral thyroid hormone levels are low (T3/T4 < normal).
Secondary Hypothyroidism:
Results from pituitary dysfunction (TSH levels < normal).
Tertiary Hypothyroidism:
Related to hypothalamic disorders impacting TRH production, therefore affecting TSH and thyroid hormone levels.
A.8 Hypothyroidism
Diagnostics:
Congenital Hypothyroidism:
Newborn Screening: Measure TSH levels within 24–48 hours after birth, as required by law.
Increased TSH Levels: Indicates potential congenital hypothyroidism.
Acquired Hypothyroidism:
Initial Assessment: Determine TSH levels to confirm or rule out the suspected diagnosis, and measure FT4 levels.
A.8 Hypothyroidism
Further Diagnostic Considerations:
Antibody Testing:
Thyroid Antibodies:
Tg Ab (Thyroglobulin Antibody) and TPO Ab (Thyroid Peroxidase Antibody): Commonly detected in patients with autoimmune thyroid conditions.
TRAb (TSH Receptor Antibody): Assessed via the thyroid-binding immunoglobulin assay (TBII).
Radiological Iodine Uptake Test:
Evaluate thyroid gland size, structure, or blood flow.
A.8 Hypothyroidism
Hashimoto’s Thyroiditis
The most prevalent cause of hypothyroidism in iodine-sufficient areas, characterized as an autoimmune disorder involving anti-TPO and anti-Tg antibodies.
Risk Factors: Increased risk of non-Hodgkin lymphoma due to B-cell proliferation.
Histology: Lymphocytic infiltration with follicular destruction is common.
Clinical Features: Typically presents as an enlarged thyroid (goiter).
A.8 Hypothyroidism
Postpartum Thyroiditis
A form of self-limited thyroiditis occurring within a year after delivery.
Symptoms: It typically resolves spontaneously and is often painless.
Histology: Similar to Hashimoto’s thyroiditis but can exhibit transient thyroid hormone fluctuations.
A.8 Hypothyroidism
Clinical Features
Symptoms Linked to Decreased Metabolic Rate:
- Fatigue and reduced physical activity
- Cold intolerance
- Weight gain
- Hair loss (accompanied by changes in appetite)
- Constipation
- Hypothyroid myopathy (elevated CK levels), muscle stiffness, and cramps
- Peripheral neuropathy (e.g., tingling and muscle weakness)
- Carpal tunnel syndrome
Symptoms Associated with Generalized Myxedema:
- Dry skin and coarse hair
- Myxedematous heart disease
Symptoms of Hyperprolactinemia (due to low TRH):
- Irregular menstrual cycles
- Galactorrhea (unexplained milk production)
- Decreased libido and erectile dysfunction in men
- Delayed ejaculation
Additional Symptoms:
- Impaired cognition (e.g., memory issues), somnolence, and depression
- Hypertension (in patients with Hashimoto’s thyroiditis or atrophic thyroiditis)
Note: Older patients may exhibit atypical symptoms of hypothyroidism; they might also show signs of dementia or depression.
A.8 Hypothyroidism
Congenital Hypothyroidism (Cretinism)
Causes: Is attributed to antibody-mediated maternal hypothyroidism, thyroid dysgenesis, or iodine deficiency, often linked to genetic mutations.
Symptoms in Children:
Physical Manifestations:
Umbilical hernia
Prolonged neonatal jaundice
Hypotonia
A.8 Hypothyroidism
Subacute Granulomatous Thyroiditis (de Quervain)
A self-limiting condition that often mimics a viral or mycobacterial infection.
Symptoms: Initial presentation may include hypertension, alongside typical symptoms of hypothyroidism in approximately 15% of cases.
Signs: Tenderness in the thyroid region, with possible signs such as fever, malaise, and jaw pain.
A.8 Hypothyroidism
Riedel Thyroiditis
The thyroid exhibits a fibrous tissue response and inflammatory infiltrate. This condition is more prevalent in older patients and can present as a hard, fixed goiter.
Symptoms: Often manifests as a non-tender, firm thyroid gland.
Treatment
Lifelong Replacement Therapy:
Levothyroxine (T4): Synthetic form of T4 used to maintain appropriate hormone levels.
Liothyronine: A synthetic form of triiodothyronine (T3), usually reserved for specific cases.
A.8 Hypothyroidism
Complications
Myxedema Coma: A severe condition resulting from advanced hypothyroidism, characterized by the body’s inability to compensate for low hormone levels. It poses a life-threatening risk, impacting about 40% of cases.
