Hyperthyroidism resident survival guide

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mydah Sajid, M.B.B.S.

Overview

Hyperthyroidism is a disease that results from thyroid hormone-induced hypermetabolism. The excess thyroid hormone is released from the thyroid gland as a result of excess thyroid hormone production, or by processes that disrupt the follicular structure of the gland with subsequent release of stored hormone. Most patients with severe hyperthyroidism present with a dramatic symptom constellation. Hyperthyroidism's typical symptoms include palpitations, heat intolerance, increased bowel movement, frequent tremors, anxiety, weight loss despite normal or increased appetite and shortness of breath. Goiter is commonly found on physical examination. As a physician, it is important to identify the severity of clinical signs, thyroid storm and treat them promptly. This section provides a short and straight-to-the-point overview of hyperthyroidism.

Causes

Life-Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Thyroid storm

Common Causes

• Graves disease
• Painless or transient (silent) thyroiditis
• Toxic adenoma (Plummer disease)
• Toxic multinodular goiter
• Postpartum thyroiditis
• Hyeremesis gravidarum
• Subacute granulomatous (de Quervain) thyroiditis
• Drug-induced thyroiditis

Diagnosis

Shown below is an algorithm summarizing the diagnosis of hyperthyroidism according to the American Thyroid Association guidelines.

Clinical assessment of signs & symptoms for hyperthyroidism: Tachycardia Palpitations Anxiety, insomnia Fine tremors in outstretched hands Heat intolerance Diaphoresis Weight loss Irregular pulse (in atrial fibrillation) Dyspnea Orthopnea Brisk deep tendon reflexes Proximal muscle weakness Pretibial myxedema (Graves’ disease) Lid lag, lid retraction, decrease lacrimation (thyroid eye disease)

Measure serum Thyroid-stimulating hormone levels

Low TSH (usually <0.01mU/L)

High TSH

Mild hyperthyroidism: Serum T4 and T3 values in normal range or only T3 levels are elevated.

Overt hyperthyroidism: Both serum T3 and T4 levels elevated

Elevated serum T4 and T3 levels

Perform thorough physical examination of thyroid gland and look for signs for thyroid eye disease. Thyroid gland diffusely enlarged with symmetrical hypertrophy and new onset of ocular symptoms

Repeat TSH levels in serial dilution

Yes. Graves' disease

No

Positive

Negative

Measure serum assays of TRAb and radioactive iodine uptake thyroid scan

High TSH levels due to hetrophilic antibodies

Look out for pituitary lesion

Measurement of serum levels of human anti-mouse antibodies

Perform MRI Brain High ratio of the serum level of alpha subunit of the pituitary glycoprotein hormone

Diffuse increase in iodine uptake

Localized increase in iodine uptake

Subnormal or absent uptake of iodine

Graves' disease

Toxic nodular goiter

Subacute thyroiditis/ Postpartum thyroiditis

Factitious ingestion of thyroid hormones

Excess intake of iodine recently

High levels of thyroglobulin in serum

Low thyroglobulin levels

Measure spot urine iodine or 24 hour urine iodine level

Treatment

Shown below is an algorithm summarizing the treatment of Graves' disease according to the American Thyroid Association guidelines.

Overt Graves' disease

Antithyroid medications

Radioactive iodine ablation

Surgery

Methimazole (MMI) is a drug of choice because of its lower side effects profile. It should be continued for a minimum duration of 12 to 18 months. Regular monitoring with TSH and TRAb should be done. Ideal in patients with: Mild disease Small goiter Pregnant females Elderly patients with cardiopulmonary comorbities

Administered in patients with: persistent thyrotoxicosis after anti-thyroid medications patients who cannot tolerate anti-thyroid medications. patients with previous neck surgery or neck irradiation. There is a risk of worsening of existing thyroid eye disease.

Total or near-total thyroidectomy is recommended for patients with: Large goiter causing compression Known or suspected thyroid malignancy Clinically moderate to severe Graves' disease Patients with cold nodules on radioactive iodine uptake scan The advantages are: High cure rate Zero recurrence rate with total thyroidectomy.

Dos

• Beta-blockers are recommended for symptomatic relief of systemic symptoms like tachycardia, anxiety, and tremors. It is strongly recommended for elderly patients with a resting heart rate greater than 90 beats per minute and coexisting cardiovascular diseases.
• The total T3 to T4 plasma levels ratio can assess the etiology of thyrotoxicosis in patients in whom the radioactive iodine uptake scan is contraindicated. An overactive thyroid gland will release more T3 compared to T4. Hence in Graves’ disease and toxic nodular goiter total T3 to T4 ratio will be high (i.e. >20), while in sub-acute or post-partum thyroiditis, the ratio of T3 to T4 will be low (i.e. <20).
• TRAb is faster and more cost-effective compared to radioactive iodine thyroid uptake scan to diagnose Graves’ disease. It should be preferred for the diagnosis of Graves’ disease.
• Near-total or total thyroidectomy is the treatment of choice for toxic multinodular goiter. Isolated lobectomy or isthmusectomy is carried out for toxic adenoma. Radioactive iodine ablation therapy have resulted in severe thyrotoxicosis with worsening of cardiac rhythms including supraventricular tachycardia, atrial flutter or atrial fibrillations in patients with non-toxic and toxic multi-nodular goiter.

Don'ts

• Pregnant, lactating females, patients with co-existing thyroid malignancy or those with high clinical suspicion of thyroid cancer should avoid radioactive iodine ablation therapy. Non-pregnant females should plan a pregnancy at least six months after RIA.
• Anti-thyroid medications are contraindicated in patients who experience anaphylaxis or serious adverse reactions from the medications.
• Elderly patients with co-existing severe cardiac, pulmonary diseases, or decreased surgical access should avoid thyroid surgery. Thyroidectomy is also contraindicated in pregnant females during the first and third trimester of pregnancy as anesthetic drugs have teratogenic effects on a developed fetus. There in an increased risk of abortion in the first trimester and preterm delivery in the third trimester. The ideal time for thyroidectomy in pregnant females is during the second trimester. There is also an increased incidence of intraoperative adverse reactions like hypocalcemia and recurrent laryngeal nerve injury in pregnant patients.

References

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