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19.8 Thyroid Disorders

Table of Contents

Thyroid disorders are conditions that affect the thyroid gland. There are specific kinds of thyroid disorders that includes hypothyroidism, hyperthyroidism, goiter, thyroid nodules and thyroid cancer.

19.8.1 Hypothyroidism

Hypothyroidism is a condition in which a person’s thyroid hormone production is below normal. Common causes of the disease is chronic autoimmune thyroiditis, post surgery and post radio active iodine.

Diagnostic criteria

The symptoms depend on the deficiency of thyroid hormone, but can include:

  • Increased cholesterol levels,
  • Depression
  • Fatigue
  • Hair loss
  • Memory loss
  • Dry, rough skin
  • Constipation
  • Hoarse voice

Investigation

A blood test is used to confirm hypothyroidism

Indications for Treatment

  • TSH level persistently > 10 mU/L; treat all patients due to, increased likelihood of progression to overt disease and a higher risk of congestive heart failure, cardiovascular disease and mortality.
  • TSH levels (4.5–10 mU/L); consider, treatment in patients younger than 65 with increased cardiovascular risk (e.g., previous cardiovascular disease, hypertension, documented diastolic dysfunction, atherosclerotic risk factors (dyslipidaemia, diabetes mellitus, smoker), goitre, positive antithyroid peroxidase antibodies, evidence of autoimmune thyroiditis by ultrasound, pregnancy, or infertility), particularly when TSH level is persistently > 7 mU/L.
  • Levothyroxine therapy could be considered also for symptomatic middle-aged patients for a short period of time. If a clear beneficial effect is observed, levothyroxine therapy could be maintained.
  • Persistently mildly increased TSH levels (>4.5–10 mU/L) with positive Thyroid Antibody and thyroid sonographic findings typical of autoimmune thyroiditis.

Pharmacological Treatment

Initial dose:

Clinical hypothyroidism–Levothyroxine 1.6–1.8 µg/kg ideal body weight
Subclinical hypothyroidism–Levothyroxine 1.1–1.2 µg/kg is recommended

  • Take at least after 2 hours fast, 30 minutes before food intake. Alternatively at bedtime (3 or more hours after the evening meal).
  • When initiating therapy in young healthy adults with overt hypothyroidism, consider beginning treatment with full replacement doses
  • Routine use of combined therapy with levothyroxine and triiodothyronine for hypothyroid patients is not recommended
  • Assess TSH and adjust dosage when there are large changes in body weight, with aging, and with pregnancy.
  • There is no convincing evidence to support routine use of thyroid extracts, L-T3 monotherapy, compounded thyroid hormones, iodine containing preparations, dietary supplementation, and over the counter preparations in the management of hypothyroidism.

Monitoring

  • TSH monitoring 6–8 weeks after any levothyroxine dose change, and yearly life– long monitoring once euthyroidism is achieved (target TSH 0.2–4.0 um/l). FT4 can be measured in early stages of treatment.
  • In patients with central hypothyroidism, assessments of serum free T4 should guide therapy and targeted to exceed the mid normal range value for the assay being used.
  • Wait for TSH equilibration–TSH equilibration requires eight to 12 weeks after any thyroxine dosage change. Once a stable dose is achieved–yearly TSH is sufficient.

In Pregnancy

When the elevation of the TSH level is confirmed, free T4 should be measured in order to classify the hypothyroidism as clinical or overt (OH) and subclinical (SH).

  • TSH > 2.5–10.0 mU/L with normal free T4: SH.
  • TSH > 2.5 –10.0 mU/L with low levels of free T4: OH.
  • TSH =10.0 mU/L, despite the level of free T4: OH

Women in reproductive period should be euthyroid before conceiving, as the hypothyroidism is associated with neural development. Dose may be doubled during pregnancy and returned to normal dose after delivery

19.8.2 Hyperthyroidism

Hyperthyroidism is a condition in which an overactive thyroid gland is producing an excessive amount of thyroid hormones that circulate in the blood. Graves’ disease, multinodular goiter (TMNG), inflammation of the thyroid gland (thyroiditis) and excessive iodine intake are the most common cause of hyperthyroidism.

Diagnostic criteria

Hyperthyroidism can be suspected in patients with

  • Tremors
  • Excessive sweating
  • Smooth velvety skin
  • Fine hair
  • A rapid heart rate
  • An enlarged thyroid glandfrequent bowel movements

Investigations

  • Baseline complete blood count, including white count with differential, and a liver profile (bilirubin and transaminases)
  • Differential white blood cell count should be obtained during febrile illness and at the onset of pharyngitis in all patients taking antithyroid medication. Routine monitoring of white blood counts is not recommended
  • Test for THS and T4
  • When thyrotoxicosis is confirmed, if cause is not known request thyroid uptake scan

Note: Management of hyperthyroidism depends on the cause

19.8.2.1 Toxic multinodular goitre or Thyroid antibody positive

Patients with overtly Toxic multinodular goitre or Thyroid antibody are treated with either:

  • Radio iodine (131-I) therapy

OR

  • Hyroidectomy

Note: Long term, low-dose carbimazole should not be used for either conditions except in some elderly

 

Surgery

  • Patients with overt hyperthyroidism should be rendered euthyroid prior to the procedure with carbimazole pre-treatment (15–40 mg daily, divided into 2–3 doses a day for 4–8 weeks then a maintenance dose of 5–15 mg, taken once daily) with or without beta–adrenergic blockade (e.g. propranolol 1—40mg 6hourly). Preoperative iodine should not be used in this setting.
  • Following thyroidectomy for Toxic multinodular goitre, it is suggested that serum calcium or intact parathyroid hormone levels be measured, and that calcitriol and oral calcium supplementation (maximum 1,200mg of calcium per day in two divided doses) be administered based on these results.
  • Following surgery for Toxic multinodular goitre, thyroid hormone replacement should be started at a dose appropriate for the patient’s weight (0.8 µg/lb or 1.7 µg/kg) and age, with elderly patients needing somewhat less. TSH should be measured every 1–2 months until stable, and then annually.

Radioiodine

  • Radioactive iodine therapy should be used for retreatment of persistent or recurrent hyperthyroidism following inadequate surgery for Toxic multinodular goitre or Thyroid antibody.

19.8.2.2 Graves hyperthyroidism

Patients with overt Graves’ hyperthyroidism should be treated with:

Medicine Initial therapy for 4–6 weeks Maintenance therapy

(gradual reduction over 3–6 months from initial dose)

C: Carbimazole 20 – 30 mg/day 5–10 mg/day

Continue for approximately 12–18 months, then taper or discontinue if TSH is normal.

Beta Blockers are used for excessive sympathetic symptoms.

B: Atenolol (PO) 50–100mg daily

Factors which favour use of antithyroid medicines

  • High likelihood of remission (patients, especially females, with mild disease, small goitres, and negative or low-titre TSH-receptor antibody)
  • Elderly or others with comorbidities increasing surgical risk or with limited life expectancy or unable to follow radiation safety regulations
  • Previously operated or irradiated necks
  • Moderate to severe active Graves’ ophthalmopathy

Radioactive iodine

Potassium iodide (B) should be given in the immediate preoperative period as 5–7 drops (0.25–0.35 mL) Lugol’s solution (8 mg iodide/drop) or 1–2 drops (0.05–0.1 mL) saturated solution of potassium iodide (50 mg iodide/drop) three times daily mixed in water or juice for 10 days before surgery

Factors which favour use of radioiodine

  • Individuals with comorbidities increasing surgical risk
  • Patients with previously operated or externally irradiated necks
  • Lack of access to a high-volume thyroid surgeon
  • Contraindications to antithyroid medicnes use
  • Females who are not pregnant and are not planning a pregnancy in the future (4–6 months) following radioiodine therapy

Surgery

Consider the following factors

  • Symptomatic compression or large goitres
  • Low uptake of radioactive iodine
  • Thyroid malignancy is documented or suspected or large non-functioning nodule
  • Coexisting hyperparathyroidism requiring surgery
  • Females planning a pregnancy in <4–6 months
  • Patients with moderate to severe active Graves’ ophthalmopathy
  • If a patient with Grave’s disease becomes hyperthyroid after completing a course of carbimazole, consideration should be given to treatment with radioactive iodine or thyroidectomy. Low-dose carbimazole treatment for longer than 12–18 months may be considered in patients not in remission who prefer this approach but evidence is that remission rate in adults is not improved by a course of medicines longer than 18 months
  • Whenever possible, patients with Grave’s disease undergoing thyroidectomy should be rendered euthyroid with carbimazole.

19.8.2.3 Thyroid storm (crisis)

Thyroid storm is one of the most life-threatening endocrine emergencies, resulting from exacerbation of manifestations of thyrotoxicosis.

Triggers of thyroid storm include:

  • Acute infections
  • Thyroidal or nonthyroidal surgeries
  • Iodinated contrast dyes
  • External beam radiation therapy.

It should be considered in very sick patients if they present with recent history of thyrotoxicosis and a recent history of precipitating factor.

Patients with thyroid storm (tachycardia, arrhythmias, congestive heart failure, hypotension, hyperpyrexia, agitation, delirium, psychosis, stupor and coma, as well as nausea, vomiting, diarrhoea, and hepatic failure) should receive a multimodal treatment including:

  • Beta-adrenergic blockade
  • Antithyroid medicine therapy
  • Inorganic iodide
  • Corticosteroid therapy
  • Aggressive cooling with acetaminophen and cooling blankets
  • Volume resuscitation
  • Respiratory support
  • Monitoring in an intensive care unit.

Thyroid storm is not a matter of thyroid levels increased beyond those of uncomplicated thyrotoxicosis, but the systemic decompensation that occurs.

Table 19.7: Pharmacological Treatment

Medicine Dosing Comment
D:

Propylthiouracil*

500–1000 mg load, then 250 mg every 4 hours Blocks new hormone synthesis Blocks T4–to–T3 conversion
C: Carbimazole 40 – 60 mg/day Blocks new hormone synthesis
A: Propranolol 60–80 mg every 4

hours

Consider invasive monitoring in congestive heart failure patients

Blocks T4–to–T3 conversion in high doses;

Alternate medicine: esmolol infusion

B: Iodine

(saturated

solution of

potassium iodide)

5 drops (0.25 mL or 250 mg) orally every 6 hours Do not start until 1 hour after antithyroid medicines

Blocks new hormone synthesis

Blocks thyroid hormone release

A:

Hydrocortisone

300 mg intravenous load, then 100 mg

every 8 hours

May block T4–to–T3 conversion

Prophylaxis against relative adrenal insufficiency

Alternative medicine: dexamethasone

Note: In thyroid storm, propylthiouracil is preferred to carbimazole

The codes will be shown below

Seconds
First: 170598
Seconds
Second: 180198

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