Published: 18 Jun 2025

ICD9: 244.9      ICD10: E03.9      ICD11: 5A00

Okay, let's break down Hashimoto's Thyroiditis and Hypothyroidism.
They are very closely related, with Hashimoto's often being the most common cause of Hypothyroidism in developed countries.

Hypothyroidism:

Definition: This is a condition where the thyroid gland doesn't produce enough thyroid hormones. Thyroid hormones (primarily thyroxine, or T4, and triiodothyronine, or T3) are crucial for regulating metabolism, which affects virtually every cell in your body.
Symptoms: Because thyroid hormones affect so much, the symptoms of hypothyroidism can be wide-ranging and often develop slowly. Common symptoms include:
Fatigue
Weight gain
Constipation
Dry skin
Hair loss
Feeling cold (even when others are warm)
Muscle aches and stiffness
Joint pain
Depression
Memory problems
Slowed heart rate
Goiter (enlarged thyroid gland - not always present)
Menstrual irregularities (in women)
Hoarse voice
Puffy face
Causes: Hypothyroidism can have various causes, including:
Autoimmune disease (Hashimoto's thyroiditis - most common)
Thyroid surgery (removal of part or all of the thyroid)
Radiation therapy to the neck (for cancer treatment)
Certain medications
Iodine deficiency (less common in developed countries where salt is iodized)
Pituitary gland problems (secondary hypothyroidism - the pituitary gland controls the thyroid)
Congenital hypothyroidism (present at birth)
Diagnosis: Hypothyroidism is diagnosed with blood tests that measure:
TSH (Thyroid-Stimulating Hormone): This is the primary test. A high TSH level usually indicates hypothyroidism. The pituitary gland produces TSH to stimulate the thyroid to make thyroid hormones. If the thyroid isn't working well, the pituitary makes more TSH to try to get it to work.
T4 (Thyroxine): A low T4 level, along with a high TSH, confirms the diagnosis. Sometimes, a "free T4" test is done, which measures the amount of T4 not bound to proteins in the blood.
T3 (Triiodothyronine): Less commonly tested, but can be helpful in some cases.
Thyroid Antibodies: To check for autoimmune conditions like Hashimoto's.
Treatment: The standard treatment for hypothyroidism is thyroid hormone replacement therapy, usually with a synthetic form of T4 called levothyroxine. The dosage is carefully adjusted based on blood tests (TSH levels) to bring the hormone levels back to normal.

Hashimoto's Thyroiditis:

Definition: This is an autoimmune disease where the body's immune system mistakenly attacks the thyroid gland. It's also known as chronic lymphocytic thyroiditis.
How it Works: The immune system produces antibodies that damage the thyroid gland, leading to inflammation and a gradual decline in its ability to produce thyroid hormones.
Relationship to Hypothyroidism: Hashimoto's is the most common cause of hypothyroidism in developed countries. The progressive damage to the thyroid eventually leads to insufficient thyroid hormone production.
Symptoms: Initially, people with Hashimoto's may not have any symptoms. As the thyroid gland is damaged, symptoms of hypothyroidism gradually appear (as listed above). Some people may experience periods of hyperthyroidism (overactive thyroid) early on, called "Hashitoxicosis," as the damaged thyroid releases stored hormones.
Diagnosis: Hashimoto's is diagnosed based on:
Blood tests:
Elevated TSH: (As thyroid function declines)
Low T4: (As thyroid function declines)
Positive Thyroid Antibodies: Specifically, anti-thyroglobulin antibodies (anti-Tg) and anti-thyroid peroxidase antibodies (anti-TPO). The presence of these antibodies confirms the autoimmune nature of the condition. It's important to note that some people may have antibodies without having clinical hypothyroidism, but they are at increased risk of developing it.
Ultrasound of the Thyroid: Sometimes used to assess the size and structure of the thyroid gland.
Treatment: There is no cure for Hashimoto's thyroiditis, but the hypothyroidism it causes is treated with levothyroxine (thyroid hormone replacement). The goal of treatment is to restore normal thyroid hormone levels and alleviate symptoms. Regular monitoring of TSH levels is essential to adjust the levothyroxine dosage as needed.

In Summary:

Hypothyroidism is the *condition* of having an underactive thyroid.
Hashimoto's Thyroiditis is a common *cause* of hypothyroidism. It's an autoimmune disease that damages the thyroid gland, leading to hypothyroidism.
Hashimoto's is like the reason *why* someone has hypothyroidism, while hypothyroidism is the *what* - what's actually wrong with their thyroid function.

Important Considerations:

Lifelong Monitoring: People with Hashimoto's or hypothyroidism usually require lifelong monitoring of their thyroid hormone levels and adjustments to their medication dosage.
Importance of Treatment: Untreated hypothyroidism can lead to serious health problems, including heart problems, infertility, and cognitive impairment.
Consult a Doctor: If you suspect you have hypothyroidism or Hashimoto's, it's essential to see a doctor for diagnosis and treatment. Don't try to self-diagnose or self-treat.
Gluten and Hashimoto's: There is some evidence that there may be a link between celiac disease and Hashimoto's, but the research is ongoing. Some people with Hashimoto's feel better when they follow a gluten-free diet, but this is not universally recommended.
Selenium: Some studies have suggested that selenium supplementation might be beneficial for people with Hashimoto's, but more research is needed. It's important to talk to your doctor before taking any supplements.

This information is for general knowledge and does not substitute professional medical advice. Always consult with your healthcare provider for any health concerns.