Untreated hyperthyroidism can cause serious complications, even death. Left unchecked, the condition can also weaken bones and cause damage to the eyes that results in double vision, blurring, and sensitivity to light. And if you are a woman who plans to have children, it can raise your risk for birth defects and miscarriages. Fortunately, proper treatment will reduce your risks. But you should still be aware of the potential for certain medical problems.

Heart Disease

Almost everyone who has hyperthyroidism experiences tachy-cardia, in which the heart beat becomes rapid and beats more than 100 times a minute. Some people may describe these as palpitations. Palpitations are sometimes a sign of an arrhythmia, in which the heartbeat has become irregular.

In addition, some people may develop an abnormal heart rhythm called an atrial fibrillation. With atrial fibrillations, the heart will have random pauses interspersed with bursts of rapid heartbeats. The condition is most likely to occur in hyperthyroid patients who have an underlying heart condition. Left untreated, atrial fibrillations can cause blood clots that lead to stroke.

Some hyperthyroid patients experience what is called high output failure. In this case, the heart is pumping so fast that it doesn't have time to fill up with blood. As a result, the heart becomes incapable of pumping enough blood to the body's organs, causing swelling and shortness of breath.

Over time, the heart is forced to work harder and harder, eventually causing death. Here are some other problems that can occur with hyperthyroidism:

• Angina: Angina describes the chest pain or squeezing sensation that occurs when the heart can't get enough oxygen as the result of plaque buildup in artery walls.

• Heart Attack: Also known as a myocardial infarction, a heart attack occurs when a coronary artery to the heart is blocked off by a blood clot, causing damage or death to the heart muscle.

• Heart Failure: Previously known as congestive heart failure, heart failure occurs when the heart can't pump enough blood to meet the body's needs, causing fatigue, shortness of breath, and fluid buildup in lungs and body tissue.

In otherwise healthy people who develop hyperthyroidism, arrhythmias and tachycardia are usually temporary conditions. But if you have other risk factors for heart disease, such as high blood pressure, high cholesterol, and obesity, hyperthyroidism can be dangerous and raise your risk for heart problems. Prompt treatment can lessen your risk, and serious heart problems can usually be averted once the hyperthyroidism is treated.

Bone Loss

Our bones are in a constant state of flux. Osteoblasts build new bone, while osteoclasts break down old bone. When you develop hyperthyroidism, these osteoclasts go into overdrive and break down bone at a rapid rate. But the osteoblasts are not affected by the excess thyroid hormone, and so they can't keep up with the destruction. The result is bone loss, and in the extreme, osteoporosis, a condition in which the bones are severely weakened.

Unless you suffer a fracture, however, you probably won't even know you have osteoporosis. The condition is painless and produces no symptoms. But if you have osteoporosis and you fall, the conditioning can become life-threatening. Bone loss is especially problematic in older, postmenopausal women, who may already have weakened bones.

Thyroid Storm

In some people, if hyperthyroidism is severe, a condition called thyroid storm may develop. Thyroid storm produces intense and severe symptoms of hyperthyroidism, primarily affecting the heart. Fortunately, the incidence of thyroid storm has gone down significantly with earlier and better treatments. That's why getting properly diagnosed and treated for hyperthyroidism is so important. In the next chapter, we'll examine your treatment options.