On the EM:RAP program, Mel Herbert and I recently did a two-part series on two rare and exotic emergencies – myxedema coma and thyroid storm. Our expert for this segment was Dr. Jonathan LoPresti, a senior endocrinologist and thyroid researcher at LA County/USC Medical Center. I interviewed him on two occasions and, quite frankly, what he had to say was fascinating. In the first part of this series, we will discuss myxedema coma. Next month we will cover thyroid storm.
Myxedema coma is one of a long list of “misnomer” diagnoses in medicine; patients with the condition are rarely edematous or comatose. Dr. LoPresti prefers to use the term “decompensated hypothyroidism”. And it is decompensated hypothyroidism that we as ER Docs need to identify and treat in the emergency department.
Dr. LoPresti has a remarkably simple and useful way of explaining what decompensated hypothyroidism is all about. Basically, patients who are hypothyroid, and thus have a decreased metabolic rate, conserve heat by being in a constant state of vasoconstriction. That is why they feel cool to the touch. They also are in a relative state of volume depletion, and although their blood pressure may be mildly elevated, they have a reduced cardiac output.
Decompensation typically occurs with infection and sepsis. These patients, who are dependent on chronic vasoconstriction to get by, suddenly have the bottom pulled out from beneath them. They are now vasodilated, volume depleted, and unable to produce enough cardiac output to cope with it. Simply stated, decompensated hypothyroidism is cardiovascular collapse in a hypothyroid patient with sepsis.
So what do these patients look like? They are cold, their skin is dry, the recovery phase of their deep tendon reflexes are delayed, their sodium and white blood cell counts are low, and there is some precipitating event going on – usually an infection. Although the formal definition of myxedema coma involves some alteration of mental status, this can be subtle: Dr. LoPresti gave the example of a patient who lost their ability to speak in a second language.
The bottom line is that it doesn’t matter to us if they meet the formal definition. If in doubt, TREAT! Despite what a lot of us have been led to believe, we have far less to worry about if we don’t treat than if we do. The only issue is the way that you treat them…
I brought up with Dr. LoPresti the fact that most EPs are afraid of intravenous thyroid hormone. Our fear is that if we give something that increases metabolism in a sick patient, that myocardial infarction and dysrhythmias may be the result. Furthermore, when the results of TSH (thyroid stimulating hormone) and other thyroid tests aren’t available in a timely fashion, the fear is worse – the last thing we want to do is give something dangerous without lab verification it was actually indicated.
Thyroxine (T4), given by intravenous push in the dose of 500 mcg, is recommended by our endocrine service in patients with suspected decompensated hypothyroidism. This dose will replete half of the typical person’s thyroid stores. This is safe and effective, explained Dr. LoPresti, and it’s not the end of the world if you turn out to be wrong about the diagnosis. When you push T4, don’t expect anything to happen right away – the vitals signs won’t change and the patient won’t look or feel any different. That’s because before T4 can exert its metabolic effects, it must be converted into its active metabolite, T3. This process takes a long time – time measured in hours and days, not minutes. Moreover, the sickest subset of patients, those with true myxedema coma, will only convert very small amounts of hormone at first, in essence, taking only what they need as the metabolism slowly starts to warm back up. Giving T3, on the other hand, which some authors have recommended, is not nearly so safe.
Before giving thyroid hormone to the cold, septic patient, you should administer hydrocortisone IV 100mg. This is because adrenal dysfunction may accompany decompensated hypothyroidism (Schmidt’s syndrome). This can be given immediately via IV push after drawing baseline cortisol levels and then followed about one hour later by the thyroxine dose.
Performing blood cultures and administering empiric antibiotics is extremely important in the decompensated hypothyroid patient. Infection is the precipitant of decompensation for the vast majority of patients and they won’t get better without aggressive sepsis treatment. On the flip side, the diagnosis of decompensated hypothyroidism should be considered in the hypothermic, septic patient who does not respond to fluids and antibiotics in the first day of treatment.
Dr. LoPresti emphasized that low blood pressure in decompensated patients should be treated principally with fluids. These patients are fluid depleted and need their volume restored. He also cautioned against the use of pressors – they can have a paradoxical effect in these patients and may make the situation worse if adequate thyroid hormone activity has not yet been achieved.
Another extremely important pearl that is contrary to what most of us have been taught is that you should not warm these patients up faster than their metabolism can handle. They will warm up on their own as they begin to experience increased thyroid hormone action, said LoPresti. Actively warming them at a rate faster than this may put them at increased risk for decompensation. It usually takes about 24 hours for these patients to warm back up completely.
In terms of diagnostic tests, both TSH and free T4 should be sent. In most cases, the TSH will be grossly elevated. Rarely, when hypothyroidism is secondary to a pituitary problem, the TSH may be normal or low, but the T4 also will be very low.
It is critical to identify this disease because mortality without hormone replacement is very high. If a TSH and T4 result is not available quickly, err on the side of replacement – don’t be afraid!
Dr. Swadron is an associate professor at the Keck School of Medicine of the University of Southern California. Along with Dr. Mel Herbert, he produces EM:RAP, the monthly audio program that can be found at www.EMRAP.org