Hypothyroidism: Symptoms, Diagnosis, and Treatment in Quebec

Persistent fatigue despite sufficient sleep. Weight gain without obvious dietary changes. Cold that is tolerated less well than before. Low mood for a few months. Each of these symptoms, taken in isolation, can be explained by a thousand things. Taken together, they form a clinical picture that doctors recognize well: that of an underactive thyroid.

Hypothyroidism is one of the most common endocrine conditions in Quebec, and one of the most underdiagnosed, precisely because its manifestations blend into the background noise of everyday life.

The role of the thyroid in the body

The thyroid is a small, butterfly-shaped gland located at the base of the neck. It produces two main hormones, thyroxine (T4) and triiodothyronine (T3), which regulate the basic metabolism of almost all organs. Heart rate, body temperature, digestion, mood, weight, fertility, and the condition of skin and hair are all influenced, directly or indirectly, by thyroid activity levels.

When the thyroid produces too little hormone, metabolism slows down. Everything slows down, in fact. This is called hypothyroidism. It affects about 5 % of the adult population in Canada, with a significantly higher prevalence in women and in individuals over 60 years of age (Thyroid Foundation of Canada, 2022).

The most frequent symptoms

Fatigue is the most frequently reported symptom. Not a fatigue that passes with a good night's sleep, but a persistent, underlying fatigue that sets in over weeks or months. It is often accompanied by a general feeling of slowness, both physical and cognitive. People sometimes describe difficulty concentrating, frequent forgetfulness, or a feeling of functioning in slow motion.

Unexplained, often modest weight gain is another common sign. It is explained by a slowing of basal metabolism. Constipation, dry skin, fragile hair that falls out more easily, brittle nails, and cold intolerance complete the classic clinical picture. In some individuals, the thyroid gland is slightly enlarged, forming what is known as a goiter, although this sign is absent in many cases.

In women of childbearing age, hypothyroidism can disrupt menstrual cycles and reduce fertility. In pregnant women, untreated hypothyroidism poses risks for fetal development, making it a condition that must be screened for and treated during pregnancy.

How is the diagnosis made

The diagnosis is based on a simple blood test. Measuring TSH, the pituitary hormone that stimulates the thyroid, is the first-line examination. High TSH indicates that the pituitary gland is working harder to try to stimulate an underactive thyroid, reflecting hypothyroidism. If the TSH is abnormal, the doctor usually follows up with a measurement of free T4 to confirm and quantify the hormonal deficiency.

In some cases, particularly when the suspected cause is autoimmune thyroiditis, anti-TPO antibody measurement can supplement the workup. Hashimoto's thyroiditis, the most common autoimmune form of hypothyroidism, is characterized by the presence of these antibodies, which progressively attack thyroid tissue.

Treatment and follow-up

Hypothyroidism is effectively treated with oral hormone replacement, usually based on levothyroxine, a synthetic form of T4. The dose is gradually adjusted based on TSH results and clinical response. Once the dose is stabilized, TSH testing every six to twelve months is sufficient in most cases to ensure hormonal balance is maintained.

The majority of treated individuals regain normal energy levels and quality of life within a few weeks to a few months. Some symptoms, such as weight gain related to hypothyroidism, gradually resolve with well-adjusted treatment.

Frequently Asked Questions about Hypothyroidism

Is hypothyroidism a permanent condition?
In most cases, yes. Hashimoto's thyroiditis, the most frequent cause, is a chronic condition that requires long-term treatment. In a few cases, particularly postpartum hypothyroidism, the condition can be transient and resolve spontaneously.

Can diet influence the thyroid?
Certain nutrients play a role in the production of thyroid hormones. Iodine is essential for the synthesis of T3 and T4. Selenium and zinc are involved in the conversion of T4 to T3. A varied and balanced diet generally covers these needs without requiring specific supplementation, except in particular cases evaluated by a doctor.

Does levothyroxine have side effects?
At the right dose, it generally does not cause side effects. An overdose can cause symptoms of hyperthyroidism: palpitations, nervousness, insomnia, weight loss. This is why regular monitoring of TSH is important to maintain balance.

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