Calcium Disorders

Introduction to Calcium Homeostasis

Calcium homeostasis is a crucial topic for MCCQE1 preparation, as it plays a vital role in many physiological processes. Understanding calcium disorders is essential for Canadian medical students aiming to excel in their licensing exams and future practice.

Key Regulators of Calcium Homeostasis

1. Parathyroid Hormone (PTH)
2. Vitamin D (Calcitriol)
3. Calcitonin

Hypercalcemia

Hypercalcemia is a common calcium disorder that MCCQE1 candidates should be well-versed in. It's defined as a serum calcium level >2.6 mmol/L (10.5 mg/dL).

Causes of Hypercalcemia

1. Primary Hyperparathyroidism (most common cause in outpatients)
2. Malignancy (most common cause in hospitalized patients)
3. Vitamin D toxicity
4. Granulomatous diseases (e.g., sarcoidosis)
5. Medications (e.g., thiazide diuretics, lithium)

Clinical Presentation

Remember the mnemonic "Stones, Bones, Abdominal Groans, and Psychic Moans" for MCCQE1 preparation:

• Stones: Kidney stones
• Bones: Bone pain, osteoporosis
• Abdominal Groans: Constipation, nausea, vomiting
• Psychic Moans: Depression, confusion, coma

Diagnostic Approach

Management

Treatment depends on the severity and underlying cause. General principles include:

1. Hydration
2. Loop diuretics (if volume overload)
3. Bisphosphonates (for severe hypercalcemia)
4. Calcitonin (for rapid, short-term calcium lowering)
5. Treatment of underlying cause

Hypocalcemia

Hypocalcemia is defined as a serum calcium level <2.1 mmol/L (8.5 mg/dL). It's an important topic for MCCQE1 candidates to understand thoroughly.

Causes of Hypocalcemia

1. Hypoparathyroidism (post-surgical or autoimmune)
2. Vitamin D deficiency
3. Chronic kidney disease
4. Hypomagnesemia
5. Acute pancreatitis

Clinical Presentation

• Neuromuscular irritability (e.g., tetany, Chvostek's sign, Trousseau's sign)
• Paresthesias
• Seizures
• QT prolongation on ECG

Diagnostic Approach

Management

1. Acute symptomatic hypocalcemia: IV calcium gluconate
2. Chronic hypocalcemia: Oral calcium and vitamin D supplements
3. Treatment of underlying cause

Canadian Guidelines for Calcium Disorders

The Canadian Society of Endocrinology and Metabolism (CSEM) provides guidelines for the management of calcium disorders. Key points for MCCQE1 preparation include:

1. Screening for primary hyperparathyroidism in asymptomatic patients is not recommended.
2. Parathyroidectomy is the definitive treatment for symptomatic primary hyperparathyroidism.
3. Vitamin D supplementation is recommended for most Canadians, especially during winter months.
4. Regular monitoring of serum calcium, phosphate, and PTH is crucial in chronic kidney disease patients.

Key Points to Remember for MCCQE1

• Understand the roles of PTH, vitamin D, and calcitonin in calcium homeostasis
• Know the major causes and clinical presentations of hypercalcemia and hypocalcemia
• Be familiar with the diagnostic approach to calcium disorders, including PTH interpretation
• Recognize the importance of vitamin D supplementation in the Canadian population
• Understand the management principles for both acute and chronic calcium disorders
• Be aware of the Canadian guidelines for calcium disorder management and calcium intake recommendations

Sample Question

A 65-year-old woman presents with fatigue, constipation, and mild confusion. Her serum calcium is 2.9 mmol/L (11.6 mg/dL), phosphate is 0.8 mmol/L (2.5 mg/dL), and PTH is 85 ng/L (normal range 10-65 ng/L). Which one of the following is the most likely diagnosis?

• A. Vitamin D toxicity
• B. Malignancy-associated hypercalcemia
• C. Primary hyperparathyroidism
• D. Familial hypocalciuric hypercalcemia
• E. Milk-alkali syndrome

Explanation

The correct answer is:

• C. Primary hyperparathyroidism

This patient presents with symptoms consistent with hypercalcemia (fatigue, constipation, confusion) and has an elevated serum calcium level. The key to diagnosis is the elevated PTH level, which is inappropriate in the setting of hypercalcemia. This combination of hypercalcemia and elevated PTH is characteristic of primary hyperparathyroidism.

Vitamin D toxicity (A) and malignancy-associated hypercalcemia (B) typically present with suppressed PTH levels. Familial hypocalciuric hypercalcemia (D) is a possibility but is less likely given the patient's age and symptoms. Milk-alkali syndrome (E) is usually associated with a history of excessive calcium intake and would have a suppressed PTH.

Remember, primary hyperparathyroidism is the most common cause of outpatient hypercalcemia in Canada and is an important topic for MCCQE1 preparation.

References

1. Canadian Society of Endocrinology and Metabolism. (2020). Clinical practice guidelines for the management of primary hyperparathyroidism. Canadian Journal of Endocrinology and Metabolism, 35(1), 1-23.

2. Health Canada. (2022). Dietary Reference Intakes: Calcium and Vitamin D. Retrieved from https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/vitamins-minerals/vitamin-calcium-updated-dietary-reference-intakes-nutrition.html (opens in a new tab)

3. Bilezikian, J. P., Brandi, M. L., Eastell, R., Silverberg, S. J., Udelsman, R., Marcocci, C., & Potts Jr, J. T. (2014). Guidelines for the management of asymptomatic primary hyperparathyroidism: summary statement from the Fourth International Workshop. The Journal of Clinical Endocrinology & Metabolism, 99(10), 3561-3569.

4. Cooper, M. S., & Gittoes, N. J. (2008). Diagnosis and management of hypocalcaemia. BMJ, 336(7656), 1298-1302.

5. Goltzman, D., Hendy, G. N., & White, J. H. (2015). Vitamin D and its receptor during late development. Biochimica et Biophysica Acta (BBA)-Molecular and Cell Biology of Lipids, 1849(2), 171-180.