Immunological Aspects of Thyroid Disorders

Immunological Basis of Endocrine Disorders

• Hashimoto Thyroiditis (Chronic Lymphocytic Thyroiditis):

  • The most common cause of goitrous hypothyroidism.
  • Most common cause of hypothyroidism in iodine-sufficient areas.
  • Typically affects middle-aged women.
  • Associated with certain HLA types (e.g., HLA-DR3).
  • Increased risk for other autoimmune diseases (e.g., Graves' disease, type 1 diabetes, SLE, non-Hodgkin lymphoma).
  • Target antigen unknown, but CD8 cells directly destroy thyroid tissue and CD4-attracted macrophages destroy thyroid tissue, releasing components into the bloodstream (like thyroglobulin and thyroid peroxidase).
  • The immune system attacks these components as if they were foreign.
  • The net result is destruction of the thyroid tissue.

• Graves' Disease (Toxic Diffuse Goiter):

  • Most common cause of hyperthyroidism.
  • Typically affects women younger than 50 more than men.
  • Associated with certain HLA types (e.g., HLA-B8).
  • Increased risk for other autoimmune diseases (e.g., type 1 diabetes, SLE).
  • Possible triggers include infectious agents (like Yersinia enterocolitica), stress, pregnancy, and environmental factors (like smoking, radiation, drugs).
  • Stimulating immunoglobulins (IgG) bind to and activate TSH receptors, overproducing thyroid hormones.
  • This leads to hyperthyroidism and a goiter.
  • Thyroid-associated ophthalmopathy can occur: Inflammatory response in retro-orbital space leading to increased orbital fat and muscle tissue and myxedema (in the skin).

• Type 1 Diabetes Mellitus (Insulin-Dependent Diabetes Mellitus):

  • Onset typically before age 30.
  • Associated with certain HLA types (e.g., HLA-DR3/4).
  • Increased risk for other autoimmune diseases.
  • Possible triggers include viral infections.
  • Autoantibodies (e.g., anti-GAD, islet cell antibodies) target and destroy insulin-producing beta cells in the pancreas.
  • This results in the body's inability to produce enough insulin.

Clinical Pictures and Diagnoses

• Hashimoto Thyroiditis:

  • Early stages: asymptomatic, gradual goiter (painless, nontoxic), possible transient hyperthyroidism ("hashitoxicosis").
  • Late stages: hypothyroidism, possible small, fibrotic thyroid.
  • Laboratory Diagnosis: anti-thyroid peroxidase (TPO) antibodies, antithyroglobulin (Tg) antibodies, and thyroid function tests (TSH, T3, T4.)

• Graves' Disease:

  • Clinical Presentation: Manifestations of hyperthyroidism (e.g., rapid heartbeat, bulging eyes (exophthalmos), goiter, pretibial myxedema).
  • Laboratory Diagnosis: Measure thyroid antibodies (TRAbs, specifically TPO and Tg antibodies), but TRAbs are more specific. Thyroid function tests (TSH, T3, T4).

• Type 1 Diabetes:

  • Laboratory Diagnosis: measuring specific autoantibodies (like anti-GAD antibodies), detecting high blood glucose and other related measures/tests (Hyperglycemia, random, fasting, glycosylated hemoglobulin A1c (HbA1c), urine tests).

General Triggers

• Genetic and environmental factors are likely involved in all these endocrine disorders.

This quiz explores the immunological basis of endocrine disorders, focusing on Hashimoto Thyroiditis and Graves' Disease. Learn about their causes, associated risks, and mechanisms of thyroid tissue destruction. Gain insights into how autoimmune responses affect thyroid health.