Myxedema is a form of tissue swelling caused by severe, prolonged hypothyroidism. Unlike typical swelling from fluid buildup, myxedema produces a distinctive thickening of the skin that doesn’t leave an indent when you press on it. The term gets used in two ways: to describe the skin changes of advanced hypothyroidism throughout the body, and as a separate condition called pretibial myxedema, which affects the shins and lower legs of people with Graves’ disease. These are different conditions with different causes, though both involve abnormal substance buildup beneath the skin.
How Myxedema Differs From Regular Swelling
Most swelling you’ve encountered, whether from a sprained ankle or heart failure, is “pitting” edema. If you press your thumb into the swollen area and hold for a few seconds, it leaves a visible dent that slowly fills back in. This happens because the fluid causing the swelling has a low protein concentration and moves easily under pressure.
Myxedema works differently. When thyroid hormone levels stay critically low for an extended period, cells in the skin called fibroblasts produce excess sugar-protein compounds (primarily hyaluronic acid) that accumulate in the deeper layers of skin. These compounds attract and trap water in a gel-like matrix rather than as free-flowing fluid. The result is skin that feels thick, doughy, and dry, with a waxy quality. Pressing on it doesn’t leave a dent. The skin can also take on a yellowish-orange discoloration, particularly over the knees, elbows, palms, and soles.
The Classic Signs of Myxedema
The most recognizable feature is what clinicians call “myxedema facies,” a characteristic set of facial changes. The face becomes puffy and swollen, especially around the eyes. The tongue enlarges noticeably, a feature called macroglossia. The outer third of the eyebrows thins or disappears entirely. Eyelids droop. Hair becomes coarse, sparse, and brittle. Taken together, these features create a distinctive appearance that can develop so gradually that family members don’t notice until it’s quite advanced.
Beyond the face, generalized myxedema affects the entire body. The skin everywhere becomes dry and thick. Voices may deepen or become hoarse as the vocal cords swell. Reflexes slow dramatically. Because thyroid hormones regulate nearly every system in the body, people with this degree of hypothyroidism also experience profound fatigue, constipation, weight gain, cold intolerance, and mental slowing that can range from brain fog to confusion.
Pretibial Myxedema: A Different Condition
Despite sharing a name, pretibial myxedema has a completely different cause. It occurs in people with Graves’ disease, an autoimmune condition that typically makes the thyroid overactive (the opposite of hypothyroidism). In Graves’ disease, the immune system produces antibodies that target thyroid hormone receptors. Skin fibroblasts on the shins also carry these receptors, and when the antibodies bind to them, the fibroblasts overproduce hyaluronic acid and other sugar compounds in the lower legs.
Pretibial myxedema shows up as raised, thickened patches of skin on the shins and tops of the feet. These patches often look pink or brownish with a waxy surface and can include lumps, scaling plaques, and significant swelling. It’s relatively uncommon, affecting between 0.5% and 4.3% of people with Graves’ disease. That number climbs to around 15% in patients who also have Graves’ eye disease. If you’ve had an injury to your lower legs, immune cells and proteins may cluster at that site, making the area more vulnerable.
Myxedema Coma: The Emergency
Myxedema coma is the most dangerous outcome of untreated or severely undertreated hypothyroidism. Despite the name, patients don’t always lose consciousness entirely. The defining feature is a combination of failing body systems: the body temperature drops (below 94°F in about 88% of cases), breathing becomes dangerously slow with low oxygen and high carbon dioxide, the heart rate slows, blood pressure falls, and mental function deteriorates from confusion to unresponsiveness.
Most cases present during winter months, when cold temperatures further stress a body that has already lost much of its ability to regulate heat. The most common triggers are infections (pneumonia, urinary tract infections, and skin infections lead the list) and stopping thyroid medication. In one study, 61% of patients who developed myxedema coma had stopped taking their thyroid supplements. Other triggers include surgery, trauma, sedative medications, and any major physical stress on a body running critically low on thyroid hormone.
Mortality remains high even with treatment. Historically, death rates ranged from 30% to 60%. A nationwide U.S. analysis from 2016 to 2020 found an overall in-hospital mortality rate of about 11.6%, reflecting improvements in critical care, though the rate rose from 6.8% in 2016 to 13.4% in 2020. Timing matters: patients admitted on weekends had a mortality rate of 13.1% compared to 8.4% for weekday admissions, likely due to reduced staffing and slower access to specialized care.
What Treatment Looks Like
For generalized myxedema that hasn’t progressed to crisis, treatment is thyroid hormone replacement. This is the same medication used for any form of hypothyroidism, just potentially started more cautiously in someone whose body has adapted to running on extremely low levels. Over weeks to months, the skin changes gradually improve as hormone levels normalize, though some thickening can persist.
Myxedema coma requires intensive hospital care. The core treatment is intravenous thyroid hormone given as a large initial dose, followed by ongoing replacement. If the patient doesn’t improve within 24 hours, a second, faster-acting form of thyroid hormone is added. Steroid hormones are also given because severely hypothyroid patients often can’t mount a normal stress response. Beyond the hormones, treatment addresses everything that’s failing: warming the body slowly, supporting breathing (many patients need a ventilator), managing low blood pressure, and treating whatever infection or event triggered the crisis. Once the patient is awake and stable, treatment transitions to the same oral thyroid medication used long-term.
Pretibial myxedema follows its own treatment path since the underlying problem is autoimmune. Mild cases may need no treatment beyond monitoring. More significant cases are typically treated with topical therapies applied to the affected skin, sometimes under wraps to improve absorption. The patches can improve, remain stable, or occasionally worsen regardless of whether the underlying Graves’ disease is controlled.
How Myxedema Is Identified
The nonpitting quality of the swelling is the key physical finding that points toward myxedema rather than other causes of edema. When a doctor presses on swollen legs from heart failure, kidney disease, or a blood clot, the skin dents and slowly rebounds. In myxedema, it doesn’t. The combination of nonpitting edema with dry, thickened skin, facial puffiness, a swollen tongue, and thinning eyebrows creates a clinical picture that’s quite distinct once it’s recognized.
Blood tests confirm the diagnosis by showing very low thyroid hormone levels and very high levels of thyroid-stimulating hormone (the signal the brain sends when it’s trying to get more hormone from a failing thyroid). For myxedema coma specifically, doctors use a scoring system that evaluates body temperature, mental status, heart function, digestive function, metabolic markers, and whether a clear triggering event is present. A score of 60 or above on this scale points strongly toward myxedema coma, while scores between 45 and 59 identify patients at risk of progressing to it.