Fatigue in Endocrinology

Introduction

Fatigue is a common complaint in primary care settings across Canada, affecting approximately 20% of patients. For MCCQE1 preparation, it's crucial to understand the endocrine causes of fatigue, their diagnosis, and management within the Canadian healthcare context.

Endocrine Causes of Fatigue

Understanding the endocrine causes of fatigue is essential for MCCQE1 success. Here are the main endocrine disorders associated with fatigue:

1. Hypothyroidism
2. Hyperthyroidism
3. Adrenal Insufficiency
4. Diabetes Mellitus
5. Hypercalcemia
6. Hypogonadism

Hypothyroidism

Hypothyroidism is a common cause of fatigue in Canadian patients, with a prevalence of about 2% in the general population.

Hyperthyroidism

Although less common than hypothyroidism, hyperthyroidism can also cause fatigue, particularly in older patients.

Adrenal Insufficiency

Adrenal insufficiency, while rare, is an important consideration in the differential diagnosis of fatigue for MCCQE1.

Diabetes Mellitus

Diabetes is a common endocrine disorder in Canada, affecting approximately 3.4 million Canadians.

Hypercalcemia

Hypercalcemia, often due to primary hyperparathyroidism or malignancy, can cause fatigue.

Hypogonadism

Hypogonadism can cause fatigue in both males and females.

Diagnostic Approach to Fatigue in Canadian Primary Care

For MCCQE1 preparation, it's crucial to understand the systematic approach to diagnosing fatigue in Canadian primary care settings.

Canadian Guidelines for Fatigue Management

The Canadian Society of Endocrinology and Metabolism (CSEM) provides guidelines for the management of endocrine disorders causing fatigue. Key points include:

1. Screening for thyroid dysfunction in all patients presenting with unexplained fatigue.
2. Using TSH as the primary screening test for thyroid disorders.
3. Considering adrenal insufficiency in patients with unexplained fatigue, especially if accompanied by hypotension or electrolyte abnormalities.
4. Screening for diabetes in patients with risk factors, using either fasting plasma glucose or HbA1c.
5. Evaluating calcium levels in patients with fatigue, especially if other symptoms of hypercalcemia are present.

Key Points to Remember for MCCQE1

• Fatigue is a common symptom in endocrine disorders, particularly hypothyroidism and diabetes mellitus.
• TSH is the most sensitive test for thyroid dysfunction and should be the initial screening test.
• Adrenal insufficiency, while rare, is a potentially life-threatening cause of fatigue that requires prompt diagnosis and treatment.
• Diabetes mellitus can present with fatigue and should be considered in patients with risk factors.
• Hypercalcemia, often due to primary hyperparathyroidism, can cause fatigue and other non-specific symptoms.
• A systematic approach to fatigue evaluation, including a thorough history, physical examination, and targeted laboratory testing, is essential for accurate diagnosis.

Sample Question

# Sample Question

A 42-year-old woman presents to her family physician with a 3-month history of progressive fatigue, weight gain of 5 kg, and constipation. She also reports feeling cold all the time. On physical examination, her heart rate is 58 bpm, and her skin feels dry and cool. Which one of the following is the most appropriate initial diagnostic test?

- [ ] A. Free T4 measurement
- [ ] B. Thyroid-stimulating hormone (TSH) measurement
- [ ] C. Thyroid ultrasound
- [ ] D. Radioactive iodine uptake scan
- [ ] E. Anti-thyroid peroxidase (anti-TPO) antibody test

Explanation

The correct answer is:

• B. Thyroid-stimulating hormone (TSH) measurement

This patient presents with classic symptoms of hypothyroidism, including fatigue, weight gain, constipation, and cold intolerance. The physical examination findings of bradycardia and dry, cool skin further support this diagnosis.

In the Canadian healthcare system, TSH is the recommended initial screening test for thyroid dysfunction. It is highly sensitive and specific for thyroid disorders. An elevated TSH would confirm the diagnosis of primary hypothyroidism, while a normal or low TSH would prompt further investigation with free T4 measurement.

Free T4 (option A) is typically measured after an abnormal TSH result to confirm the diagnosis and determine the severity of hypothyroidism.

Thyroid ultrasound (option C) and radioactive iodine uptake scan (option D) are not initial diagnostic tests for hypothyroidism. They may be used later to evaluate thyroid nodules or determine the cause of hyperthyroidism.

Anti-TPO antibody testing (option E) can help identify the etiology of hypothyroidism (e.g., Hashimoto's thyroiditis) but is not the most appropriate initial test for diagnosis.

References

1. Toward Optimized Practice (TOP) Endocrine Working Group. (2014). Investigation and management of primary thyroid dysfunction clinical practice guideline. Edmonton, AB: Toward Optimized Practice. Available from: https://actt.albertadoctors.org/CPGs/Pages/Thyroid-Dysfunction.aspx (opens in a new tab)

2. Diabetes Canada Clinical Practice Guidelines Expert Committee. (2018). Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes, 42(Suppl 1):S1-S325.

3. Gao, T., & Koch, C. A. (2015). Fatigue and Endocrine Disorders. In De Groot LJ, Chrousos G, Dungan K, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279129/ (opens in a new tab)

4. Canadian Society of Endocrinology and Metabolism. (2021). Clinical Practice Guidelines. Available from: https://www.endo-metab.ca/guidelines (opens in a new tab)

5. Public Health Agency of Canada. (2017). Diabetes in Canada: Facts and figures from a public health perspective. Ottawa, ON: Public Health Agency of Canada. Available from: https://www.canada.ca/en/public-health/services/publications/diseases-conditions/diabetes-canada-highlights-chronic-disease-surveillance-system.html (opens in a new tab)