**7. Diagnosis for the iodine-induced thyroid dysfunction in respondents**

Both insufficient and excessive iodine intake can result in thyroid dysfunctional diseases. If the thyroid diseases are due to iodine-induced phenomena, the main management is to avoid or reduce iodine intake, followed by the appropriate drugs if symptomatic or there is abnormality with the thyroid function test (TFT) results.

## **7.1 Iodine-induced hypothyroidism**

Iodine-induced hypothyroidism can occur in normal individuals and in those with chronic systemic disease and underlying thyroid disorders. It has been seen in patients who had a history of post-partum thyroiditis and subacute thyroiditis and in those treated with recombinant interferon-alpha. The hypothyroidism was described as transient, and thyroid function returns to normal in 2–3 weeks after iodide withdrawal. Some patients may require transient T4 replacement therapy [23].

#### *7.1.1 Clinical presentation*

The presenting clinical features of hypothyroidism depend on the duration and severity, the nature of its onset and the patient's psychological characteristics [24]. The following are the signs and symptoms of hypothyroidism:

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*Urinary Iodine: Biomarker for Population Iodine Nutrition*

*DOI: http://dx.doi.org/10.5772/intechopen.84969*

• Weight gain from fluid retention

• Dry skin and cold intolerance

• Coarseness or loss of hair

• Reflex delay, relaxation phase

• Memory and mental impairment

• Irregular or heavy menses and infertility

• Myxoedema fluid infiltration of tissues

When there is clinical suspicion of hypothyroidism, a thyroid function test should be performed. Measurement of TSH level is the primary test to confirm primary hypothyroidism. Other laboratory evaluation may include free T4 and thyroid antibodies (anti-thyroid peroxidase and anti-thyroglobulin autoantibodies). Imaging studies to evaluate any structural thyroid abnormalities include a thyroid scan, ultrasonography or both [24]. When iodine deficiency occurs during pregnancy, it is associated with foetal hypothyroidism, mental impairment and increased neonatal and infant mortality [25]. In adults, iodine-induced hypothyroidism is rare. The most common manifestation is goitre. Low iodine intake leads to reduced T4 and T3 production which results in increased TSH secretion in an attempt to restore normal T4 and T3 production. TSH also stimulates thyroid growth leading to goitre. The goitre is initially diffuse but progresses to nodular goitre and eventually to thyroid autonomy and possible hyperthyroidism [26]. Excess iodine ingestion or exposure above the limit of the recommended daily iodine intake induces thyroid dysfunction. Iodine-induced thyroid dysfunction may be subclinical or overt. Excess iodine is generally well tolerated. However,

• Decreased concentration

• Fatigue

• Yellow skin

• Hoarseness

• Goitre

• Ataxia

• Constipation

• Depression

• Myalgias

*7.1.2 Diagnosis*

• Hyperlipidaemia

• Bradycardia and hypothermia

*Urinary Iodine: Biomarker for Population Iodine Nutrition DOI: http://dx.doi.org/10.5772/intechopen.84969*

• Fatigue

*Biochemical Testing - Clinical correlation and Diagnosis*

TPOAb and 31 kIU/L for TgAb [22] (**Figure 4**).

**7.1 Iodine-induced hypothyroidism**

*7.1.1 Clinical presentation*

synthesis, thus causing lower thyroid hormone production. TgAb is the antibody for the globulin TG. With the presence of elevated amount of TgAb, the thyroglobulin (TG) will bind to its antibody, and lesser TG is available to bind to the thyroid hormones for transportation in the blood vessels, thus causing lesser thyroid hormones being circulated in the human body [21]. The reference intervals are 15 kIU/L for

*Subsequent biomarker testing and further action for individual and population urinary iodine estimation.*

**7. Diagnosis for the iodine-induced thyroid dysfunction in respondents**

Iodine-induced hypothyroidism can occur in normal individuals and in those with chronic systemic disease and underlying thyroid disorders. It has been seen in patients who had a history of post-partum thyroiditis and subacute thyroiditis and in those treated with recombinant interferon-alpha. The hypothyroidism was described as transient, and thyroid function returns to normal in 2–3 weeks after iodide with-

The presenting clinical features of hypothyroidism depend on the duration and severity, the nature of its onset and the patient's psychological characteristics [24].

drawal. Some patients may require transient T4 replacement therapy [23].

The following are the signs and symptoms of hypothyroidism:

Both insufficient and excessive iodine intake can result in thyroid dysfunctional diseases. If the thyroid diseases are due to iodine-induced phenomena, the main management is to avoid or reduce iodine intake, followed by the appropriate drugs if symptomatic or there is abnormality with the thyroid function test (TFT) results.

**20**

**Figure 4.**


#### *7.1.2 Diagnosis*

When there is clinical suspicion of hypothyroidism, a thyroid function test should be performed. Measurement of TSH level is the primary test to confirm primary hypothyroidism. Other laboratory evaluation may include free T4 and thyroid antibodies (anti-thyroid peroxidase and anti-thyroglobulin autoantibodies). Imaging studies to evaluate any structural thyroid abnormalities include a thyroid scan, ultrasonography or both [24]. When iodine deficiency occurs during pregnancy, it is associated with foetal hypothyroidism, mental impairment and increased neonatal and infant mortality [25]. In adults, iodine-induced hypothyroidism is rare. The most common manifestation is goitre. Low iodine intake leads to reduced T4 and T3 production which results in increased TSH secretion in an attempt to restore normal T4 and T3 production. TSH also stimulates thyroid growth leading to goitre. The goitre is initially diffuse but progresses to nodular goitre and eventually to thyroid autonomy and possible hyperthyroidism [26]. Excess iodine ingestion or exposure above the limit of the recommended daily iodine intake induces thyroid dysfunction. Iodine-induced thyroid dysfunction may be subclinical or overt. Excess iodine is generally well tolerated. However,

individuals with underlying thyroid disease or other risk factors may be susceptible to iodine-induced thyroid dysfunction following acute or chronic exposure.

*7.1.2.1. Predisposing risk factors in iodine-induced hypothyroidism*

Individuals with underlying thyroid disease:


The spectrum of iodine deficiency disorders (IDD) is seen across the life span in various age groups, i.e. foetus, neonate, infants, child, adolescent and adult. They include endemic goitre and cretinism, endemic mental retardation, decreased fertility rate, increased perinatal death and infant mortality and varying degrees of other growth and developmental abnormalities (**Table 3**) [27, 28]. Hypothyroidism due to very low iodine intake is now extremely rare. Adults usually have the typical clinical manifestations of hypothyroidism and goitres [29].


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*Urinary Iodine: Biomarker for Population Iodine Nutrition*

The symptoms and signs include the following:

Iodine-induced hyperthyroidism can occur after intake of excess iodine in the diet, exposure to radiographic contrast media for imaging procedures or medications [30]. In iodine-sufficient areas, iodine can induce hyperthyroidism in euthyroid patients with previous thyroid diseases. These include patients who were treated with anti-thyroid drugs for Grave's disease and post-partum

The severity and spectrum of symptoms and signs of hyperthyroidism may be related to the duration of the illness, the effects of excess thyroid hormone and the

*DOI: http://dx.doi.org/10.5772/intechopen.84969*

**7.2 Iodine-induced hyperthyroidism**

thyroiditis [31, 32].

*7.2.1 Clinical presentation*

age of the patient [24].

• Tremor

• Weight loss or gain

• Sudden paralysis

• Impaired fertility

• Mental disturbances

• Fatigue and muscle weakness

• Goitre (depending on cause)

• Pretibial myxoedema

• Alterations in appetite

• Nervousness and irritability

• Palpitations and tachycardia

• Heat intolerance or increased sweating

• Frequent bowel movements or diarrhoea

• Dependent lower-extremity oedema

• Exertional intolerance and dyspnoea

• Menstrual disturbance (decrease flow)

• Sleep disturbances (including insomnia)

• Changes in vision, photophobia, eye irritation, diplopia or exophthalmos

#### **Table 3.**

*The spectrum of IDD across the life span.*
