What Happens If Hypothyroidism Is Left Untreated?

If hypothyroidism is left untreated or not adequately treated, the disease can progress and lead to profound coma or even death.

Hypothyroidism (underactive thyroid) is an endocrine disorder that occurs when a person’s body does not make enough thyroid hormone. The thyroid gland is located in the neck and produces thyroid hormone that controls how the body uses and stores energy. 

One form of hypothyroidism is autoimmune thyroid disease, also called Hashimoto’s disease or Hashimoto's thyroiditis. Myxedema coma is a severe form of hypothyroidism.

The opposite of hypothyroidism is hyperthyroidism, a condition in which the body produces too much thyroid hormone.

Symptoms of hypothyroidism may be subtle and some people may have no symptoms. 

Common symptoms of hypothyroidism may include:

• Fatigue
• Lethargy
• Loss of energy
• Weight gain
• Decreased appetite
• Cold intolerance  
• Dry skin
• Hair loss
• Sleepiness
• Muscle pain
• Joint pain
• Weakness in the extremities
• Depression
• Mood swings 
• Cognitive impairment
• Problems concentrating
• Forgetfulness/memory impairment
• Constipation
• Menstrual disturbances
• Impaired fertility
• Decreased sweating
• Numbness, tingling, and nerve entrapment syndromes
• Blurred vision
• Hearing loss
• Feeling of fullness in the throat
• Hoarseness
• Nail problems such as infection, vertical white ridges on the nails, nail splitting, brittle nails, slow nail growth, and nails lifting up 

Other less common symptoms of hypothyroidism may include:

• Slowed speech and movements
• Yellowing skin and eyes (jaundice)
• Pale skin (pallor)
• Coarse, brittle, straw-like hair
• Coarse facial features
• Dull facial expression
• Swelling around the eyes
• Enlarged tongue
• Goiter (simple or nodular)
• Slow heart rate 
• Decreased systolic blood pressure (upper number) and increased diastolic blood pressure (lower number)
• Excess fluid around the heart (pericardial effusion)
• Pitting edema of lower extremities
• Sub-normal reflexes with delayed relaxation, loss of coordination, or both
• Abdominal distention, fluid in the abdominal cavity (ascites) (uncommon)

Symptoms more specific to Hashimoto thyroiditis include:

• Painless thyroid enlargement
• Feeling of fullness in the throat
• Exhaustion
• Temporary neck pain, sore throat, or both

Symptoms of myxedema coma (severe hypothyroidism) include:

• Altered mental status
• Low core body temperature (hypothermia)
• Slow heart rate
• Too much carbon dioxide (CO2) in the bloodstream
• Low blood sodium levels
• Enlarged heart, fluid around the heart, cardiogenic shock, and ascites 
• Nonpitting edema

In the U.S. and other countries where iodine intake is adequate, the most common cause of hypothyroidism is autoimmune thyroid disease (Hashimoto’s disease). 

Worldwide, iodine deficiency is the main cause of hypothyroidism.

A doctor will take a medical history and perform a physical examination, but blood tests are used to diagnose hypothyroidism. 

Blood tests used to diagnose hypothyroidism include:

• Thyroid-stimulating hormone (TSH)
• Thyroxine (T4)
• Triiodothyronine (T3)
• Thyroid antibody tests

Hypothyroidism is treated with thyroid hormone replacement therapy. 

• Levothyroxine (LT4) (Synthroid, Levoxyl, Levothroid, Unithyroid) is most commonly used
• In some cases, another form of thyroid hormone, liothyronine (T3) (Cytomel, Triostat), may be given with T4
  • Since T4 is converted into triiodothyronine (T3) in other organs, most studies have not shown an advantage of combining T3 and T4 over using T4 alone
• Women may need higher doses of T4 during pregnancy

If hypothyroidism is left untreated or not adequately treated, the disease can progress and lead to profound coma or even death. 

Other complications that can arise if hypothyroidism is left untreated include: 

• Myxedema coma (severe hypothyroidism)
• Miscarriage and pre-eclampsia during pregnancy
• Heart disease
• Nerve damage
• Enlarged thyroid gland (goiter)
• Infertility
• Birth defects and developmental problems
• Depression
• Delayed puberty in children

Hypothyroidism during pregnancy result in obstetric complications such as:

• Preeclampsia (high blood pressure during pregnancy)
• Low birth weight
• Anemia
• Postpartum bleeding
• Cardiac ventricular dysfunction
• Increased risk of spontaneous abortion/fetal death
• Impaired fetal cognitive development 

Hypothyroidism may cause complications in patients with certain mental illness:

• Patients with depression may develop mania
• Psychosis may worsen in patients with severe psychiatric illness

If not treated promptly, hypothyroidism in infants can cause complications such as:

• Irreversible mental retardation 
• Slowed physical and linear bone growth
• Delayed dental development

In most cases, proper treatment with thyroid replacement therapy can reverse signs and symptoms of hypothyroidism and patients can live a normal life span.