Do you know about the THIRD type of autoimmune thyroid disease?
Atrophic Thyroiditis causes hypothyroidism, but it’s NOT Hashimoto’s.
Myths and lack of knowledge
Most doctors and patients have never heard about Atrophic Thyroiditis (AT). That’s because it’s not taught in med school, and an ultrasound is not usually ordered unless a thyroid gland is enlarged or has nodules.
An atrophied thyroid is NOT “end-stage” Hashimoto’s — that’s a common myth.
Thyroid glands do NOT normally shrink with age — that’s also a common myth.
The surprising facts
Believe it or not, AT is actually a HYPOthyroid form of Graves’ disease.
There’s even an article that calls atrophic thyroiditis “Hypothyroid Graves’ disease” (Starrenburg-Razenberg et al 2010)
The normal form of Graves’ HYPERthyroidism is caused by TSH-Receptor *stimulating* antibodies that overstimulate the thyroid gland to produce hormone, even in the absence of TSH.
But Atrophic Thyroiditis is the mirror image of Graves’ disease. It is caused by TSH-Receptor *blocking* antibodies that prevent TSH, even extremely high levels of TSH, from stimulating the thyroid gland. This form of thyroid disease may also present with Hashimoto’s antibodies.
According to Frohlich 2016, “Thyroid Autoimmunity,” blocking anti-TSH-Receptor antibodies occur in 25–75% of Graves’ Disease patients.
Jara, 2009 explains that Atrophic Thyroiditis patients usually have a Graves’ disease genetic profile, which is distinct from Hashimoto’s.
You can flip between hypo and hyper status
According to Takasu et al, 2012, Graves’ disease patients can flip between hypothyroid, hyperthyroid and euthyroid status over many years, depending on whether the blocking antibody predominates over the stimulating antibody, or whether the two antibodies are in balance with each other. TSHR antibody levels can fluctuate wildly and can also completely disappear or resurface over time.
A real example — one of us
One of our team members in the Canadian Thyroid Patients Campaign has atrophic thyroiditis.
A normal female gland is about 12-15 mL volume. Her gland is 0.5 mL, a size that is found in less than 2% of autoimmune thyroid patients, according to Carle et al, 2009.
She was without hypothyroid symptoms until her late 20s. In her early 30s she presented with a TSH over 150. Throughout her 13 years on Synthroid, she continued to have a high and variable TSH level despite T4 in the upper part of normal reference range.
Common signs and diagnosis
A very high TSH (over 50) at diagnosis and a variable TSH over time are common findings in studies of Atrophic Thyroiditis. TSH can be so variable and biased by antibodies that TSH becomes a distraction, not a useful measure of hypothyroidism, so Free T4 and Free T3 testing is necessary.
Atrophic Thyroiditis can be diagnosed by ultrasound measurements and a TBII test, (Thyrotropin-Binding Inhibitory Immunoglobulin) (Khoo et al, 1999).
TBII tests measure both stimulating and blocking TSHR antibodies and add them together to yield a single number, which is very high in AT when blocking antibodies are active.
See this blog post for a link to our larger collection of sources on this topic: