Thyroid Disorders

Thyroid gland produces 2 hormones –

1. Thyroxine or T₄ and
2. Triiodothyronine or T₃.

Functions of the thyroid hormones are:

• · They help in cell differentiation
• · Maintain temperature and metabolism.

Disorders of Thyroid are due to

• 1. Overproduction ofthyroid hormone – Thyrotoxi­cosis
• 2. Decreased production of thyroid hormone – Hy­pothyroidism
• 3. Thyroid -nodules
• 4. Thyroid cancers.
• The thyroid glant has two lobes connected by an isth­mus.
• Weight is 12-20 gms.
• It is highly vascular and soft.
• 4 parathyroid glands are situated behind the thyroid glands.
• Thyroid medullary C cells produce calcitonin hormone which has the effect of lowering the calcium levels.

Abnormalities associated with development of thyroid gland may be –

• · Ectopic thyroid
• · Lingual thyroid
• · Thyroglossal duct cysts
• · Thyroid agenesis
• · Congenital hypothyroidism (1 in 4000 new-borns).
• Thyrotoxicosis factitia is due to self administration of thyroid hormones and not a true thyroid disease.
• TSH or thyroid stimulating hormone is secreted by anterior pituitary under the influence of TRH or thy­rotropin releasing hormone.

Biofeedback :

• Thyroid hormones have a negative feedback on the release of TSH and TRH i.e.
• when the level of thyroid hormones in the blood is high, TSH release is decreased.

Examination of the Thyroid

• The skin is typically warm and moist, and the hair may be thin and fine.
• The patient is examined from the front and side for· any masses, prominent veins or scar.
• The thyroid is palpated from behind the patient with both hands. The patient is asked to swallow and the thyroid is palpated for size, consistency, nodules and tenderness.
• The physical examination may be notable for hyperactivity and rapid speech.
• Many patients have stare (lid retraction) and lid lag, representing sympathetic hyperactivity
• In increased vasculatiry of the gland, a bruit is found over the gland.
• In retrosternal goiters, venous distention is seen over the neck, with difficulty in breathing especially when the arms are raised above the head (Pemberton’s sign).
• Tachycardia is common, the pulse is irregularly irregular in patients with atrial fibrillation, systolic hypertension may be present,
• Lymphadenopathy of supraclavicular and cervical lymph nodes is examined.
• Tremor, proximal muscle weakness, and hyperreflexia are other frequent findings.
• Exophthalmos, periorbital and conjunctival edema, limitation of eye movement, and infiltrative dermopathy (pretibial myxedema) occur only in patients with Graves’ disease.

Thyroid Disorders Laboratory tests

• TSH is assayed to see if level is suppressed, normal or elevated.
• In primary abnormality of thyroid function, TSH level may be suppressed or elevated, but never normal.
• In thyrotoxicosis, TSH is suppressed.
• In hypothyroidism, TSH levels are elevated.
• Always free T₃ and T₄ are estimated as the total T₃ and T₄ are highly protein-bound and are affected by illness or medications.
• To confirm thyrotoxicosis, free T₄ level elevation is sufficient.
• Elevated TSH level is not enough to confirm hypothy­roidism, therefore TSH and free T₄ should both be done.
• Autoimmune thyroid disease is detected by measur­ing antibody against thyroid peroxidase and thyro­globulin.
• Radio-iodine uptake and thyroid scanning helps to determine thyroid function and localize nodules and cancers.
• Fine-needle aspiration biopsy of thyroid is used to evaluate thyroid nodules.
• Thyroid ultrasound is used to detect nodule and cysts more than 3 mm.