Thyroid Disease

FY1 Sejal Nirban

Thyroid Gland

Predominantly secretes T4 and small amounts of T3

Most T3 is produced by peripheral conversion of T4

Iodine is an essential requirement for thyroid hormone synthesis

99% of T4 and T3 circulate bound to plasma proteins (Thyroid Binding Globulin)

Free hormones are available to control the metabolic rate of many tissues

Thyroid function is measured using Serum TSH and free T4 and T3

Hyperthyroidism

Affects 1/50 females and 1/250 males

Due to an excess of T3 and T4 causing thyrotoxicosis

An acute exacerbation of symptoms is called a thyrotoxic crisis- usually brought on by infection

Diagnosis is made by measuring TSH, free T3 and free T4

Raised TSH suggests the fault is in the pituitary or hypothalamus whereas low TSH is due to a thyroid problem

  Symptoms

  Weight loss

  Increased appetite

  Heat intolerance

  Palpitations

  Fatigue

  Sweating

  Diarrhoea

  Oligomenorrhoea

  Psychiatric symptoms

  Irritability

  Emotional lability

  Psychosis

  Signs

  General

  Hair thinning

  Goitre

  Lid lag, lid retraction

  Pre-tibial myxoedema

  Eye signs

  Palmar erythema

  CVS

  Tachycardia

  AF

  Neuro

  Fine tremor

Causes:

  1. Graves Disease- most common cause. IgG antibodies bind to TSH receptor stimulating thyroid hormone production
  2. Toxic Multinodular Goitre
  3. Solitary adenoma
  4. De Quervains Thyroiditis- acute inflammation of thyroid gland (fever, malaise and neck pain)
  5. Postpartum thyroiditis

Management:

  1. Anti-thyroid drugs: Carbimazole (UK) Methimazole (USA)- both block thyroid hormone biosynthesis and also have immunosuppressive affects. Clinical benefit is not seen for 10-20 days. Carbimazole can cause agranulocytisis- seek urgent blood count if patient develops unexplained fever or sore throat
  2. Beta blockers: Propanolol used for symptomatic control
  3. Radioactive Iodine: contraindicated in pregnancy and breast feeding. Accumulates in the gland and results in local irridation
  4. Surgery: thyroidectomy can only be performed in euthyroid patients. Complications of surgery include bleeding, hypocalcaemia and hypothyroidism.

Thyroid Storm

Life threatening condition- severe thyrotoxicosis

Precipitated by infection, stress and surgery

Treated with large doses of carbimazole, propranolol, potassium iodide and hydrocortisone

Graves’ Disease

Goitre

Eye signs- oedema, proptosis, lid retraction, lid lag, and opthalmoplegia- worse in smokers.

Thyrotoxicosis

Cause: T lymphocytes react with antigens shared by the orbit and thyroid leads to retro orbital inflammation. Swelling and oedema of extra-ocular muscles leading to limitation of movement and proptosis. Increased pressure on the optic nerve may cause optic atrophy.

Treatment is low dose of carbimazole, surgery or radioiodine and stop smoking advice

Hypothyroidism

Affects 1/100 females and 1/500 males. Incidence increases with age.

T3 and T4 levels are low with a raised TSH

If TSH is low then there is likely to be a hypothalamic or pituitary lesion

  Symptoms

  Weight gain

  Fatigue, lethargy

  Cold intolerance

  Constipation

  Menorrhagia

  Hoarse voice

  Myalgia

  Carpal tunnel syndrome

  Psychiatric symptoms

  Depression

  Dementia

  Signs

  General

  Dry skin and hair

  Goitre

  Non-pitting oedema

  Facial features – purple lips, malar flush, periorbital oedema, lateral eyebrow loss

  CVS

  Bradycardia

  Neuro

  Cerebellar ataxia

  Slow relaxing reflexes

  Peripheral neuropathy

Causes

  1. Iodine deficiency
  2. Autoimmune thyroiditis- Hashimoto’s thyroiditis
  3. Iatrogenic- thyroidectomy, radioactive iodine
  4. Drug induced- carbimazole, lithium, Amiodarone
  5. Congenital hypothyroidism- thyroid aplasia

Management: Lifelong Levothyroxine. Aim to normalise TSH

Myxoedema coma

Severe hypothyroidism with swelling of subcutaneous tissues- typically around eyes and back of hands ‘’bunch of banana hands’’

Unresponsive, decreased respiratory rate, low bp, low glucose, low temperature

Pregnancy and Thyroid

·  Increased concentration of TBG

·  Total T4 and T3 increase

·  Free T4 and T3 remain within normal range

·  TSH does not change

Two pregnancy-related hormones—human chorionic gonadotropin (hCG) and estrogen—cause increased thyroid hormone levels in the blood. Made by the placenta, hCG is similar to TSH and mildly stimulates the thyroid to produce more thyroid hormone. Increased estrogen produces higher levels of thyroid-binding globulin.

Transient autoimmune thyroiditis can occur postpartum resulting in hypo or hyperthyroidism

Hyperthyroid management: Propylthiouracil. Carbimazole is associated with congenital defects including aplasia cutis of the neonate.

Hypothyroid management: Levothyroxine is safe to give in pregnancy

Thyroid Malignancy

Most present as asymptomatic thyroid nodules

Types:

  1. Papillary- 70%. Good prognosis
  2. Follicular- 20%. Good prognosis
  3. Anaplastic <5%. Aggressive, poor prognosis
  4. Lymphoma 2%. Poor prognosis
  5. Medullary 5%. Often familial. Poor prognosis

Investigation: FNAC distinguishes between benign and malignant nodules

Treatment: Radioactive iodine, thyroidectomy with wide local lymph node excision. External radiotherapy and palliative care for anaplastic and lymphomas.