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Hypothyroidism
Decreased production of thyroid hormones or tissue resistance leads to diminished
thyroid activity termed as hypothyroidism. It is manifested majorly by a reversible
slowing of all bodily functions [1]. There are three types of hypothyroidism: primary, secondary and tertiary hypothyroidism (also known as central hypothyroidism). Primary hypothyroidism is characterised by low level of thyroid hormones
primarily caused by destruction of thyroid glands [9]. It accounts for more than 95%
of adult cases. Central hypothyroidism is caused by insufficient stimulation of thyroid glands secondary to hypothalamic or pituitary disorders and is associated with
decreased levels of T3, T4 and normal or low levels of TSH. Patients with central
hypothyroidism have either a failure of the anterior pituitary to secrete TSH (also
known as secondary hypothyroidism), failure of the hypothalamus to secrete thyroid releasing hormone (TRH) known as tertiary hypothyroidism, or, in some rare
cases, a TSH deficiency with no other findings of pituitary or hypothalamus abnormality. The most common cause of central hypothyroidism is pituitary mass lesions.
Treatment, such as surgery or radiation therapy for these lesions, can also lead to
central hypothyroidism [10].
Clinical Manifestations of Hypothyroidism
Slow metabolic rate, slow speech, deep hoarse voice, sensitivity to cold, dry skin,
bradycardia, mental impairment, hypercholesterolemia, lethargy and myxoedema
(subcutaneous deposition of glycosaminoglycan’s induced characteristic thickening
of skin along with hypothyroidism) are common signs and symptoms of hypothyroidism. Patients presented with these signs and symptoms along with increased
TSH and decreased T4 and/or T3 levels are diagnosed with clinical (overt) hypothyroidism. However, biochemical findings of serum TSH levels above and serum T4
and/or T3 levels within the reference range indicate subclinical hypothyroidism
[9, 11].
Aetiology of Hypothyroidism
The most common causes of hypothyroidism are autoimmune destruction of thyroid glands (Hashimoto’s thyroiditis), radiation, thyroidectomy, iodine deficiency and drugs. The congenital hypothyroidism is most common endocrine
disorder among infants (1 in every 3000–4000) caused by deficiency of thyroid
hormones during foetal development. It leads to growth and mental retardation
among children [3].
6 Impaired Thyroid Function in Metabolic Disorders
Hypothyroidism
Decreased production of thyroid hormones or tissue resistance leads to diminished
thyroid activity termed as hypothyroidism. It is manifested majorly by a reversible
slowing of all bodily functions [1]. There are three types of hypothyroidism: primary, secondary and tertiary hypothyroidism (also known as central hypothyroidism). Primary hypothyroidism is characterised by low level of thyroid hormones
primarily caused by destruction of thyroid glands [9]. It accounts for more than 95%
of adult cases. Central hypothyroidism is caused by insufficient stimulation of thyroid glands secondary to hypothalamic or pituitary disorders and is associated with
decreased levels of T3, T4 and normal or low levels of TSH. Patients with central
hypothyroidism have either a failure of the anterior pituitary to secrete TSH (also
known as secondary hypothyroidism), failure of the hypothalamus to secrete thyroid releasing hormone (TRH) known as tertiary hypothyroidism, or, in some rare
cases, a TSH deficiency with no other findings of pituitary or hypothalamus abnormality. The most common cause of central hypothyroidism is pituitary mass lesions.
Treatment, such as surgery or radiation therapy for these lesions, can also lead to
central hypothyroidism [10].
Clinical Manifestations of Hypothyroidism
Slow metabolic rate, slow speech, deep hoarse voice, sensitivity to cold, dry skin,
bradycardia, mental impairment, hypercholesterolemia, lethargy and myxoedema
(subcutaneous deposition of glycosaminoglycan’s induced characteristic thickening
of skin along with hypothyroidism) are common signs and symptoms of hypothyroidism. Patients presented with these signs and symptoms along with increased
TSH and decreased T4 and/or T3 levels are diagnosed with clinical (overt) hypothyroidism. However, biochemical findings of serum TSH levels above and serum T4
and/or T3 levels within the reference range indicate subclinical hypothyroidism
[9, 11].
Aetiology of Hypothyroidism
The most common causes of hypothyroidism are autoimmune destruction of thyroid glands (Hashimoto’s thyroiditis), radiation, thyroidectomy, iodine deficiency and drugs. The congenital hypothyroidism is most common endocrine
disorder among infants (1 in every 3000–4000) caused by deficiency of thyroid
hormones during foetal development. It leads to growth and mental retardation
among children [3].
6 Impaired Thyroid Function in Metabolic Disorders