Hypothyroidism Disease

BASICS

DESCRIPTION

A clinical state resulting from decreased circulating levels of free thyroid hormone or from resistance to hormone action. Myxedema connotes severe hypothyroidism.

System(s) affected: Endocrine/Metabolic
Genetics:
- No known genetic pattern for idiopathic primary hypothyroidism
- Hypothyroidism may be associated with Type II autoimmune polyglandular syndrome, which is associated with HLA-DR3, DR4
- Secondary hypothyroidism frequently results from treatment for Graves disease, which may be familial
Incidence/Prevalence in USA:
- 5–10/1000 in general population
- Over age 65, increases to 6–10% of women, 2–3% of men
Predominant age: Over 40
Predominant sex: Female > Male, 5-10:1

SIGNS AND SYMPTOMS

Symptoms
- Onset may be insidious, subtle
- Weakness, fatigue, lethargy
- Cold intolerance
- Decreased memory
- Hearing impairment
- Constipation
- Muscle cramps
- Arthralgias
- Paresthesias
- Modest weight gain (10 pounds [4.5 kg])
- Decreased sweating
- Menorrhagia
- Depression
- Hoarseness
- Carpal tunnel syndrome
Signs
- Dry, coarse skin
- Dull facial expression
- Coarsening or huskiness of voice
- Periorbital puffiness
- Swelling of hands and feet
- Bradycardia
- Hypothermia
- Reduced systolic blood pressure
- Increased diastolic blood pressure
- Reduced body and scalp hair
- Delayed relaxation of deep tendon reflexes
- Macroglossia
- Dilutional hyponatremia
- Anemia (usually normochromic, normocytic)
- Enlarged heart on chest x-ray (often due to pericardial effusion)

CAUSES

Post-ablative follows radioactive iodine therapy or thyroid surgery. Delayed hypothyroidism may develop in patients treated with thioamide drugs (propylthiouracil, methimazole) 4 to 25 years later.
Primary hypothyroidism may develop as a result of autoimmune thyroiditis, or be idiopathic
With goiter, most commonly due to autoimmune disease, such as Hashimoto's thyroiditis; or heritable biosynthetic defects, iodine deficiency (rare in the US), or drug induced (iodides, lithium, phenylbutazone, aminosalicylic acid)
Suprathyroid hypothyroidism may be due to deficiency of thyrotropin-releasing hormone (TRH) from the hypothalamus or thyroid-stimulating hormone (TSH) from the pituitary
Transient hypothyroidism may result from silent thyroiditis (most common in postpartum period) and subacute granulomatous thyroiditis

RISK FACTORS

Risk increases with increasing age
Autoimmune diseases

DIAGNOSIS

LABORATORY

Total serum thyroxine (T4) - decreased
T3 resin uptake - increased
TSH (radioimmunoassay) - elevated
Free T4 index (= T3 resin uptake × total serum T4) - low
In severe hypothyroidism: anemia, elevated cholesterol, CPK, LDH, AST, hyponatremia

Drugs that may alter lab results:

Thyroid supplement
Cortisone
Dopamine
Phenytoin
Estrogen or androgen therapy in excess of replacement
Amiodarone
Salicylates

Disorders that may alter lab results:

Any severe illness
Pregnancy
Chronic protein malnutrition
Hepatic failure
Nephrotic syndrome

PATHOLOGICAL FINDINGS

Thyroid may be small, atrophic or enlarged

SPECIAL TESTS

Radioimmunoassay

IMAGING

None necessary

DIAGNOSTIC PROCEDURES

Elevated TSH (greater than 20 µU/mL [3-20 mIU/L]) is diagnostic of primary thyroid failure

TREATMENT

APPROPRIATE HEALTH CARE

Outpatient except for complicating emergencies (coma, hypothermia)

GENERAL MEASURES

Goals of treatment are to restore and maintain a euthyroid state

SURGICAL MEASURES

N/A

ACTIVITY

As tolerated

DIET

High-bulk diet may be helpful to avoid constipation
Low fat diet for obese patients

PATIENT EDUCATION

Importance of compliance with thyroid replacement therapy
Need for lifelong treatment
Report to physician any signs of infection, heart problems
Signs of thyrotoxicity

FOLLOW UP

PREVENTION/AVOIDANCE

N/A

POSSIBLE COMPLICATIONS

Treatment induced congestive heart failure in people with coronary artery disease
Myxedema coma - life threatening complication of hypothyroidism
Increased susceptibility to infection
Megacolon
Organic psychosis with paranoia
Adrenal crisis with vigorous treatment of hypothyroidism
Infertility
Hypersensitivity to opiates
Overtreatment over long periods can lead to bone demineralization

EXPECTED COURSE AND PROGNOSIS

With early treatment, striking transformations in appearance and mental function. Return to normal state is the rule.
Relapses will occur if treatment is interrupted
If untreated, may progress to myxedema coma

MISCELLANEOUS

ASSOCIATED CONDITIONS

Hyponatremia
Anemia
Idiopathic adrenocorticoid deficiency
Diabetes mellitus
Hypoparathyroidism
Myasthenia gravis
Vitiligo
Hypercholesterolemia
Mitral valve prolapse
Depression
Rapid cycling bipolar disorder

AGE-RELATED FACTORS

Pediatric: N/A
Geriatric:

Characteristic signs and symptoms frequently changed or absent. Hypothyroidism is common in elderly. Diagnosis based on laboratory criteria.
Replacement therapy is usually about two thirds of the dose used in young adults.

Others: N/A

PREGNANCY

Replacement therapy may need adjustment. TSH levels should be monitored monthly during first trimester.
Postpartum - check TSH levels at about 6 weeks
Painless subacute thyroiditis may occur in the postpartum period, leading to transient hypothyroidism lasting about 3 months. Treatment with replacement therapy may be warranted. Up to 30% of these individuals develop permanent hypothyroidism.

OTHER NOTES

Surgical procedures
- Hypothyroid patients (mild to moderate) tolerate surgery with mortality and complications similar to euthyroid patients
- If surgery is elective, render patient euthyroid prior to procedure
- If surgery is urgent, proceed with the procedure with individualized replacement therapy preoperatively and postoperatively

ABBREVIATIONS

N/A

Clinical Investigations

ROLE OF HOMOEOPATHY

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