Introduction 

Hypothyroidism is a clinical syndrome caused by insufficient thyroid hormone production

-it is 10 times more common in females than in males

-Thyroxine (T4) and triiodothyronine (T3) are the thyroid hormones

-Peripherally, thyroxine T4 is converted to the active triiodothyronine T3

-T3 is three to four times more potent than thyroxine T4. 

-Primary hypothyroidism is caused by the intrinsic dysfunction of the thyroid gland. -The most common cause is Hashimoto’s thyroiditis

-other causes: surgical removal, ablation of thyroid gland 

Secondary hypothyroidism is caused by a deficiency of thyroid-stimulating hormone (TSH) from the pituitary gland or deficiency of thyrotropin-releasing hormone from the hypothalamus

Drug induced hypothyroidism: Amiodarone, lithium, α-interferon, interleukin etc can also cause hypothyroidism 

Symptoms & Signs 

Symptoms: headaches, hair loss, fatigue,lethargy, depression, shortness of breath, constipation, weight gain, menstrual irregularities, infertility, muscle cramps, joint pains, paresthesias, cold intolerance, carpal tunnel syndrome, dysphagia, neck discomfort, decreased hearing  

Signs: Puffy face, periorbital puffiness, loss of outer third of eyebrows, pallor, thickening of the tongue, hoarseness, bradycardia, diastolic hypertension, hypoventilation, absent or decreased bowel sounds, edema, delayed relaxation of ankle jerks, peripheral neuropathy, cool, rough, dry skin, yellowing of skin, thin brittle nails, hypothermia, thinning of hair, peripheral edema, delayed relaxation of deep tendon reflexes, cardiac enlargement (myxedema heart), psychosis (myxedema madness), altered mental status (myxedema coma) 

Diagnosis 

-The single best screening test for hypothyroidism is the serum TSH

-Primary hypothyroidism: High TSH (stimulating the failing gland), with low total or free thyroxine T4 and triiodothyronine T3

-Secondary hypothyroidism: Low TSH with low total or free thyroxine T4 and triiodothyronine T3

-Imaging: CT or MRI may show a goiter in the neck, pituitary hyperplasia 

Treatment 

Synthetic levothyroxine is the preferred medication for treating hypothyroidism