Hypercalcemia with suppressed PTH indicates that elevated calcium levels are not caused by parathyroid overactivity. Common causes include:

1. Malignancies:
   • Paraneoplastic Syndrome: Tumors (e.g., lung or breast cancer) produce parathyroid hormone-related peptide (PTHrP).
   • Bone Metastases: Increase bone resorption and calcium release.
   • Ectopic Vitamin D Production: Lymphomas may activate vitamin D, enhancing calcium absorption.
2. Vitamin D Intoxication:
   • Excessive intake of vitamin D supplements raises intestinal calcium absorption.
3. Granulomatous Diseases:
   • Conditions like sarcoidosis or tuberculosis activate vitamin D within granulomas, increasing calcium levels.
4. Medications and Diet:
   • Thiazide Diuretics: Reduce calcium excretion via the kidneys.
   • Lithium: Alters calcium regulation.
   • Milk-Alkali Syndrome: Excessive calcium and alkaline substance intake can cause hypercalcemia, kidney dysfunction, and calcification.
5. Immobilization:
   • Prolonged inactivity can increase bone resorption and calcium release, especially in patients with preexisting bone disorders.
6. Endocrine Disorders:
   • Adrenal Insufficiency: May reduce renal calcium excretion.
   • Hyperthyroidism: Increases bone turnover and calcium release.

Treatment focuses on managing the underlying cause of hypercalcemia while monitoring calcium and PTH levels.

Hypercalcemic Crisis

Summary:
A hypercalcemic crisis is a life-threatening condition characterized by severely elevated calcium levels in the blood, typically exceeding 3.5 mmol/L (14 mg/dL). Symptoms include confusion, kidney failure, heart rhythm disturbances, and severe dehydration. Treatment involves:

• Intravenous fluids to rehydrate and promote calcium excretion.
• Loop diuretics (e.g., furosemide) to enhance calcium excretion.
• Bisphosphonates to inhibit bone resorption.
• Calcitonin for rapid calcium reduction.
• Glucocorticoids for specific causes.
• Dialysis in severe cases.

The underlying condition must also be treated.

Symptoms of a Hypercalcemic Crisis

1. Neurological Symptoms:
   • Confusion, disorientation, and coma.
2. Gastrointestinal Symptoms:
   • Nausea, vomiting, abdominal pain, constipation.
3. Cardiovascular Symptoms:
   • Heart rhythm disturbances, high blood pressure.
4. Renal Symptoms:
   • Dehydration, kidney failure, excessive urination, or anuria (no urine output).
5. Skeletal Symptoms:
   • Bone pain, muscle weakness.

Treatment of Hypercalcemic Crisis

The primary goal of treatment is to rapidly lower calcium levels and address the underlying cause. Key interventions include:

1. Rehydration:
   • Intravenous administration of large volumes of isotonic saline (0.9% NaCl) to restore intravascular volume and enhance calcium excretion via the kidneys.
2. Diuretics:
   • Loop diuretics (e.g., furosemide) are used after adequate hydration to increase calcium excretion.
   • Thiazide diuretics are contraindicated as they enhance calcium reabsorption.
3. Bisphosphonates:
   • Zoledronic acid or pamidronate inhibit bone resorption and reduce calcium levels.
   • Their effect begins after 24–48 hours, making them suitable for sustained calcium control.
4. Calcitonin:
   • Provides rapid but short-lived reduction of calcium levels. It is particularly useful in the initial hours of treatment while waiting for bisphosphonates to take effect.
5. Glucocorticoids:
   • Corticosteroids (e.g., prednisone) are effective in hypercalcemia caused by vitamin D intoxication or granulomatous diseases by reducing intestinal calcium absorption.
6. Dialysis:
   • Hemodialysis with calcium-free dialysate is reserved for severe cases, especially in patients with kidney failure or when medications are ineffective.
7. Treatment of the Underlying Condition:
   • Addressing the cause of hypercalcemia (e.g., malignancy, vitamin D overdose) is essential to prevent recurrence.

Management Considerations

• Intensive Monitoring:
  • Continuous monitoring of calcium levels, kidney function, and vital signs is critical.
• Multidisciplinary Care:
  • Involvement of endocrinologists, nephrologists, and oncologists ensures comprehensive management.

Hypercalcemic crisis is a medical emergency that requires immediate and aggressive intervention to prevent life-threatening complications and ensure patient survival.