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Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Hashimoto thyroiditis

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In one line

·Your own immune system slowly destroys your thyroid gland, so the gland makes less and less thyroid hormone over time.

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Normal physiology

·The thyroid gland sits in the front of your neck and makes thyroid hormone—mostly T4 and a little T3—that travels through your blood and tells every cell how fast to work. A small gland in your brain, the pituitary, watches the blood and sends out TSH when thyroid hormone drops, telling the thyroid to make more. Think of TSH as the pituitary's phone call to the thyroid saying 'we need more hormone.' This feedback loop keeps your body's energy level steady.

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What goes wrong

·Your immune system's B cells and T cells, which normally attack bacteria and viruses, start making antibodies and inflammatory signals against thyroid peroxidase (TPO)—the enzyme your thyroid needs to build hormone. Over months and years, this chronic attack damages and kills thyroid cells, so the gland shrinks and makes less T4 and T3. As thyroid hormone drops, your pituitary sees the low level and pumps out more and more TSH trying to whip the dying gland into action, but the gland cannot respond because too many of its cells are dead.

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Hallmark signs

·Tired all the time, even after sleeping
·Weight gain without eating more
·Feeling cold when others feel fine
·Dry skin and hair; hair falls out more
·Constipation (hard to poop)
·Goiter (a swelling in the front of the neck)
·Trouble thinking clearly or remembering things
·Heavy or irregular periods

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Red flags · escalate now

·Sudden, severe swelling in the neck that makes it hard to breathe or swallow (could mean bleeding into the thyroid or a dangerous infection)
·Heart rate under 50 or trouble staying awake, feeling very confused, or body temperature under 95°F (signs of myxedema coma, a life-threatening shutdown from very low thyroid hormone)
·A hard, fixed lump in the thyroid that doesn't move (raises concern for thyroid cancer, which is rare but needs urgent check)

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Workup

·TSH (thyroid-stimulating hormone)
·Free T4 (thyroxine, the main thyroid hormone)
·Anti-TPO antibodies (antibodies against thyroid peroxidase, the enzyme that builds thyroid hormone)
·Anti-thyroglobulin antibodies (antibodies against thyroglobulin, the storage protein for thyroid hormone)
·Thyroid ultrasound
·Free T3 (triiodothyronine, the active form of thyroid hormone)

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Treatment

·Levothyroxine (synthetic T4, the main thyroid hormone)
·Check TSH and free T4 every 6–8 weeks after starting or changing the dose
·Start with a lower dose (25–50 micrograms per day) in elderly patients or anyone with heart disease
·Take levothyroxine on an empty stomach, 30–60 minutes before breakfast, with water only
·Screen for other autoimmune diseases (type 1 diabetes, celiac disease, vitiligo, Addison disease, pernicious anemia)
·Recheck thyroid function once a year after the dose is stable

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NCLEX trap

·In Hashimoto thyroiditis, start levothyroxine (the thyroid hormone pill) slowly, especially in older people or anyone with heart trouble. Too much too fast can make the heart race or skip beats. Check TSH again in 6 to 8 weeks. The goal is to replace what the body is missing, not to rush a number back to normal.
·The swollen thyroid in Hashimoto thyroiditis often shrinks on its own over time as the immune attack keeps destroying cells. Levothyroxine replaces the missing hormone but does not stop the immune attack or make the goiter disappear faster. The goiter shrinks because the gland is dying, not because medicine healed it.
·Tiredness in Hashimoto thyroiditis comes from low thyroid hormone slowing down every cell in the body, not from sadness or mood. Replace the hormone with levothyroxine first. The tiredness usually lifts when T4 levels come back up. Always check TSH and free T4 before calling fatigue depression.
·Hashimoto thyroiditis never goes away. The immune system keeps attacking the thyroid for life, and the damaged gland cannot make enough hormone. Levothyroxine replaces what the dying gland cannot make. TSH stays normal only because the patient takes the medicine every day. Stop the medicine and TSH climbs back up within weeks.
·Antibodies in Hashimoto thyroiditis show the immune system attacked the thyroid in the past and will likely attack again, but the antibody number does not tell you how active the attack is today. Replace the missing hormone with levothyroxine. We do not use immune-blocking drugs for Hashimoto thyroiditis unless the patient has another autoimmune disease that needs treatment on its own.
·This is myxedema coma — a life-threatening emergency from very low thyroid hormone in untreated or under-treated Hashimoto thyroiditis. The brain and body shut down. This patient needs emergency IV levothyroxine, careful warming, ICU monitoring, and treatment of any infection or trigger. Do not miss this — it can kill.

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