Hyperthyroidism with Hashimoto's: the rare overactive phase, and what to write down

Short answer: Hyperthyroidism with Hashimoto's can happen, and the US sources call it rare. NIDDK says most people with Hashimoto's disease develop hypothyroidism, an underactive thyroid, and that rarely, early in the course of the disease, thyroid damage may lead to the release of too much thyroid hormone into your blood, causing symptoms of hyperthyroidism. The American Thyroid Association (ATA) lists Hashimoto's thyroiditis as causing hypothyroidism, with "rare cases of transient thyrotoxicosis", its term for high thyroid hormone levels in the blood. The name hashitoxicosis appears in MedlinePlus, from the US National Library of Medicine, which marks it very rare in its TSI test entry, and in a 2018 case report by doctors in New York. Mayo Clinic says that if you notice a rapid heartbeat, unusual sweating or other symptoms of hyperthyroidism, make an appointment with your healthcare professional and tell them about all the symptoms you've noticed, even if they are minor. The ATA says your doctor works out the cause of hyperthyroidism from your physical exam findings, labs and imaging.

If you have Hashimoto's and you've had a stretch where your heart raced and sleep wouldn't come, this is for you. Wanting a name for that is reasonable. So is wanting it written down before your next appointment.

Osmi's daily check-in is one place to keep it. It takes about a minute: answer seven questions or speak with Rose, your thyroid mascot, and every answer lands on the same record as your labs, cycle, and sleep.

How an underactive condition can have an overactive spell

The ATA's thyroiditis page covers Hashimoto's alongside other kinds of thyroiditis, and it splits the damage into two speeds.

The ATA says slow, chronic damage to thyroid cells leads to a fall in thyroid hormone and the symptoms of hypothyroidism, and that this would be the case in Hashimoto's thyroiditis.

Rapid damage works differently. When thyroiditis causes rapid thyroid cell damage, the ATA says, "the thyroid hormone that is stored in the gland leaks out, increasing thyroid hormone levels in the blood." The ATA says the symptoms are similar to hyperthyroidism, and adds that "in thyrotoxicosis, the gland is not truly overactive." It describes this for the toxic phase of subacute, painless and postpartum thyroiditis. Mayo Clinic describes the same leak when it lists thyroiditis as a cause of hyperthyroidism: the inflammation can cause extra thyroid hormone stored in the gland to leak into the bloodstream.

For Hashimoto's itself, the ATA's table lists hypothyroidism with rare cases of transient thyrotoxicosis, and says the hypothyroidism is usually permanent.

What each US source says, and the word it uses

So the word you may have read online is real. It just isn't the word on most of these pages. NIDDK's Hashimoto's and hyperthyroidism pages don't use it, and neither do the ATA's, Mayo Clinic's or Cleveland Clinic's. If your doctor says thyrotoxicosis, a hyperthyroid phase or hashitoxicosis, write down the word they used, so the next person reading your notes sees the same one.

How long it lasts, and what comes after

None of the US patient pages from NIDDK, the ATA, Mayo Clinic or MedlinePlus gives a timeline for the overactive spell of Hashimoto's on its own. The ATA's hyperthyroidism page speaks about thyroiditis in general: hyperthyroidism due to thyroiditis "is usually self-limited, meaning that it goes away on its own after a few weeks to months", and in some cases hypothyroidism can follow. One case report, from 2018, says the phase usually lasts one to two months, though the case it describes lasted two years.

If the overactive spell came after a birth, the ATA describes postpartum thyroiditis, which causes temporary thyrotoxicosis followed by temporary hypothyroidism. For what to write down, see postpartum thyroiditis.

What it can feel like

NIDDK says symptoms of hyperthyroidism can vary from person to person and may include a rapid or irregular heartbeat, weight loss despite an increased appetite, shaky hands, sweating or trouble tolerating heat, and trouble sleeping. The ATA's list includes feeling like your heart is racing or beating irregularly, and changes in menstrual periods, often lighter and/or less frequent. The ATA also says you may not have all the symptoms, and that they can start suddenly or come on slowly over time.

Mayo Clinic says hyperthyroidism sometimes looks like other health conditions, which can make it hard to diagnose. NIDDK says a hyperthyroidism diagnosis can't be based on symptoms alone, because many of its symptoms are the same as those of other diseases. So keep the dates with the symptoms.

What to write down

Mayo Clinic's appointment advice for hyperthyroidism includes this: "Write down any symptoms you have, including any that may seem unrelated to the reason you scheduled the appointment." It also says your healthcare professional is likely to ask when your symptoms began, whether they've been continuous or occasional, and how severe they are. A record that answers those three questions is worth bringing.

1. Each symptom, the date it started, and the date it eased, if it has.
2. Whether it was there every day or came and went, and how bad it felt, in your own words.
3. Your heart rate, if you wear a ring or a watch. In Osmi, connect Oura, WHOOP, or Apple Health, and your sleep, heart rate, and exercise land on the same record as your labs and your symptoms. It saves you typing. It doesn't detect anything.
4. Anything new in your neck. NIDDK's list of hyperthyroidism symptoms includes an enlargement in the neck, called a goiter, and the ATA's includes trouble swallowing or fullness in the neck.
5. Your periods, with dates.
6. Every medicine you take, vitamins and supplements included, which Mayo Clinic asks you to list before the visit.
7. Every blood result, with its date, its lab and the range printed on the report.

Osmi's lab album holds that last one. Photograph the paper, upload the PDF, or type one number. Osmi files every result with its unit, date, lab and printed range, and a re-draw stacks on the same card and shows what moved. Osmi doesn't tell you what a result means about you. Where two things line up, it says they track with each other and it stops there.

What your doctor may check

The ATA says that to determine which condition is causing hyperthyroidism, "your doctor will review your physical exam findings, labs, and imaging." It names Graves' disease as the most common cause and thyroiditis as another. The blood tests it lists are thyroid hormone levels (TSH, T4 and T3) and thyroid antibodies, including TSI, TRAb and TPO antibodies. The imaging it lists is a thyroid ultrasound or a nuclear medicine scan. Mayo Clinic says that if blood tests show hyperthyroidism, a radioiodine scan and uptake test or a thyroid ultrasound can help find out why your thyroid is overactive.

For how the two autoimmune conditions differ, see Graves' vs Hashimoto's. For what the antibody tests are, see thyroid antibodies, explained.

Questions to take to your appointment

Mayo Clinic's own list of questions for hyperthyroidism includes:

• "What's the most likely cause of my symptoms?"
• "Are there other possible causes?"
• "What tests do I need?"
• "Is my condition likely temporary or long-lasting?"
• "Should I see a specialist?"

And a few more for this situation:

• What word are you using for this, and can you write it down for me?
• Which antibodies have I been tested for, and when?
• When do you want to recheck my levels?
• What would you want me to call you about before then?

Osmi's appointment sheet is one page, built from the record you already keep, that you share with your practitioner in one tap. It doesn't diagnose anything and it doesn't read your results for you.

When it can't wait

Mayo Clinic says a rare condition called thyroid storm requires emergency medical care, and that its symptoms may include fever, fast heartbeat, nausea, vomiting, diarrhea, dehydration and confusion. Cleveland Clinic's advice: "If you’re experiencing signs of thyroid storm, like a high fever and very fast heart rate, get to the nearest hospital as soon as possible."

One small thing to start with: write down the date your symptoms began. It's the first question on Mayo Clinic's list of what your doctor is likely to ask.

Questions women ask about hyperthyroidism with Hashimoto's

What is hashitoxicosis? MedlinePlus, from the US National Library of Medicine, names hashitoxicosis in its entry on the TSI blood test and marks it very rare. A 2018 case report by doctors at Mount Sinai in New York describes it as the initial hyperthyroid phase of patients with Hashimoto's thyroiditis. NIDDK and the ATA describe an overactive spell in Hashimoto's without using the word: NIDDK as symptoms of hyperthyroidism, rarely, early in the course of Hashimoto's disease, and the ATA as rare cases of transient thyrotoxicosis.

How rare is an overactive phase with Hashimoto's? NIDDK says it happens rarely, and the ATA's thyroiditis table lists rare cases. MedlinePlus marks hashitoxicosis very rare in its TSI test entry. None of those pages gives a number. NIDDK says most people with Hashimoto's disease develop hypothyroidism, and that rarely, the disease can cause hyperthyroidism, or overactive thyroid.

How long does the overactive phase of Hashimoto's last? The ATA's Hashimoto's, thyroiditis and hyperthyroidism pages don't give a separate timeline for Hashimoto's. For thyroiditis in general, the ATA says hyperthyroidism is usually self-limited and goes away on its own after a few weeks to months. One 2018 case report says this phase usually lasts one to two months, and describes one that lasted two years. Ask your doctor when they want to recheck your levels.

Can Hashimoto's make your heart race? NIDDK says that rarely, early in the course of Hashimoto's disease, thyroid damage may cause symptoms of hyperthyroidism, and its list of hyperthyroidism symptoms includes a rapid or irregular heartbeat. NIDDK also says many of those symptoms are the same as those of other diseases. Mayo Clinic says that if you notice a rapid heartbeat, make an appointment with your healthcare professional.

How do doctors find out why a thyroid is overactive? The ATA says your doctor will review your physical exam findings, labs and imaging. The blood tests it lists include TSH, T4, T3 and thyroid antibodies, and the imaging it lists includes a thyroid ultrasound or a nuclear medicine scan. Mayo Clinic says a radioiodine scan and uptake test or a thyroid ultrasound can help find out why your thyroid is overactive.

When is an overactive thyroid an emergency? Mayo Clinic says thyroid storm is a rare condition that requires emergency medical care, with symptoms that may include fever, fast heartbeat, nausea, vomiting and confusion. Cleveland Clinic says that if you're experiencing signs of thyroid storm, like a high fever and very fast heart rate, get to the nearest hospital as soon as possible.

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Educational, not medical advice.