Can Lyme Disease Cause Hypothyroidism?

“The answer is yes,” says the BCA Clinic. “Lyme disease . . . can cause hypothyroidism in some people.”

My doctor of internal medicine says many of her Lyme patients develop hypothyroidism. She too believes the disease leads to an underactive thyroid.

My First Hints I Might Have Hypothyroidism

Before I was diagnosed with Lyme, I suspected I might have an underactive thyroid. After all, they share many symptoms. 

But my first clear sign I had a thyroid problem emerged at my initial appointment with my Lyme specialist. During her physical exam, she discovered a two- to three-centimeter nodule on my thyroid. Dr. McIntyre assured me many people have thyroid nodules, and they’re usually not cancerous. Even so, I needed to get an ultrasound. 

The ultrasound revealed two nodules, including one that needed to be biopsied. So, I got an endocrinologist. He biopsied the bigger nodule, but the lab results showed it wasn’t cancer. Still, I’ll always need to get regular ultrasounds.

Fast-forward to my first appointments with my doctor of internal medicine. 

Among the labs she ordered, some were for my thyroid. They showed my T3 Uptake was low, and my Free Thyroxine Index was at the bottom of the normal range: 1.2 where normal is 1.2 to 4.9. But the main reasons she gave for suspecting hypothyroidism were my symptoms and my TSH level of 3.69. 

Though a level of 1.0 is ideal, many doctors don’t diagnose you with hypothyroidism until you hit 4.0. Looking back on my previous labs, though, my TSH levels were consistently climbing. Dr. Brinkley didn’t want to just wait around until they passed the magic number. 

“If your TSH level is above 2.8,” she said, “there’s only a fifteen percent chance you don’t have hypothyroidism.”

Did Lyme Disease Cause Our Family’s Hypothyroidism?

Seven years ago, my dad had early disseminated Lyme disease. Within two years of that, he was diagnosed with hypothyroidism. Likewise, I was diagnosed with late-stage Lyme in 2018 and hypothyroidism in 2019. 

My dad and I both suspected Lyme may have caused our underactive thyroid. What really sealed the deal, though, was when my daughter’s TSH levels came back high. 

Michaela had early Lyme last summer. By this June, her TSH level was already 4.3. She’s only eight. 

If our hypothyroidism were genetic, wouldn’t we all be diagnosed around the same age? Instead, my dad was diagnosed in his late fifties, me in my early forties, and Michaela in grade school. 

Plus, none of my dad’s parents, siblings, or blood nephews or nieces have hypothyroidism. (The only exception is one nephew who had thyroid cancer and had to have his thyroid removed.)

Dr. Brinkley started me on Synthroid to help my underactive thyroid. The following month, December 2019, I would be diagnosed with two more things.

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