Causes
There are several distinct causes for chronic hypothyroidism. Historically and, still, in many developing countries iodine deficiency is the most common cause of hypothyroidism world-wide. In present day developed countries, however, hypothyroidism is mostly caused by Hashimoto’s thyroiditis, or by a lack of the thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary.

Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year after giving birth. The first phase is typically hyperthyroidism. Then, the thyroid either returns to normal or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring life-long treatment.

Early symptoms

Poor muscle tone (muscle hypotonia)
Fatigue
Cold intolerance, increased sensitivity to cold
Constipation
Weight gain
Muscle cramps and joint pain
Thin, Brittle fingernails
Thin, brittle hair
Paleness

Late symptoms

Slowed speech and a hoarse, breaking voice. Deepening of the voice can also be noticed.
Dry puffy skin, especially on the face
Thinning of the outer third of the eyebrows
Abnormal menstrual cycles
Low basal body temperature

Less common symptoms
Heat intolerance, increased sensitivity to heat
Impaired memory
Impaired cognitive function (brain fog) and inattentiveness
Urticaria (hives)
Migraine headache
A slow heart rate with ECG changes including low voltage signals. Diminished cardiac output and decreased contractility.
Reactive (or post-prandial) hypoglycemia[8]
Pericardial effusions may occur.
Sluggish reflexes
hair loss
Anemia caused by impaired hemoglobin synthesis (decreased EPO levels), impaired intestinal iron and folate absorption or B12 deficiency from pernicious anemia
anxiety/panic attacks
difficulty swallowing
Shortness of breath with a shallow and slow respiratory pattern.
Impaired ventilatory responses to hypercapnia and hypoxia.
Increased need for sleep
Osteopenia or Osteoporosis
Irritability and mood instability
Yellowing of the skin due to impaired conversion of beta-carotene to vitamin A
Impaired renal function with decreased GFR.
Thin, fragile or absent cuticles
Elevated serum cholesterol
Acute psychosis (myxedema madness) is a rare presentation of hypothyroidism
Decreased libido
Decreased sense of taste and smell (late, less common symptoms)
Puffy face, hands and feet (late, less common symptoms)