Hypercalcemia: CHIMPANZEES Causes, Diagnosis & Treatment

Q: How do I differentiate primary hyperparathyroidism from malignancy-related hypercalcemia?

PTH level is the key: primary HPT has elevated or inappropriately normal PTH with hypercalcemia. Malignancy suppresses PTH to near zero. Check PTHrP (elevated in humoral hypercalcemia of malignancy — squamous cell, RCC), 24h urine calcium, vitamin D levels, and SPEP. Primary HPT is usually chronic and asymptomatic; malignancy-related is acute, severe, and symptomatic.

Q: Why should furosemide not be used first-line for hypercalcemia?

Loop diuretics can worsen hypercalcemia if the patient is volume-depleted by increasing proximal tubular calcium reabsorption. IV normal saline must be given first to ensure adequate volume status and promote urinary calcium excretion. Furosemide is only added after euvolemia is established and only if the patient is at risk for fluid overload.

The 60-second version

Primary hyperparathyroidism = most common cause overall (high PTH + high Ca); malignancy = most common inpatient cause (suppressed PTH)
CHIMPANZEES mnemonic covers all causes; check PTH first to distinguish PTH-mediated from non-PTH-mediated
Symptoms: bones, stones, groans, psychic moans; ECG shows shortened QT interval
Treatment: IV normal saline first, then bisphosphonates (zoledronic acid) for malignancy-related; calcitonin for rapid bridge
Steroids for vitamin D-mediated hypercalcemia (sarcoid, lymphoma); parathyroidectomy for primary HPT meeting surgical criteria

Causes of Hypercalcemia: CHIMPANZEES

The CHIMPANZEES mnemonic covers all major causes: **C**alcium supplementation excess, **H**yperparathyroidism (primary — most common overall; tertiary in CKD), **I**mmobilization (increased bone resorption), **M**ilk-alkali syndrome, **P**aget disease (primarily with immobilization), **A**ddison's disease (adrenal insufficiency), **N**eoplasm/malignancy (second most common overall; most common inpatient cause — PTHrP, osteolytic mets, lymphoma via 1,25-OH-D), **Z**ollinger-Ellison (MEN1), **E**xcess vitamin D (granulomatous diseases: sarcoid, TB, histoplasma — macrophages convert 25-OH-D to active 1,25-OH-D), **E**ctopic PTH (rare), **S**arcoidosis and other granulomatous diseases. Primary hyperparathyroidism: high PTH + high calcium (50% asymptomatic, found on routine labs). Malignancy: suppressed PTH + very high calcium (PTHrP from squamous cell, renal, bladder cancers; osteolytic mets from breast, myeloma; lymphoma via calcitriol).

Clinical Features and Diagnosis

**Bones**: osteitis fibrosa cystica (primary HPT), pathologic fractures, subperiosteal bone resorption (radial aspect of middle phalanx on X-ray — classic HPT sign). **Stones**: nephrolithiasis (calcium oxalate/phosphate stones), nephrocalcinosis, nephrogenic DI, polyuria. **Groans**: nausea, vomiting, constipation, anorexia, peptic ulcers (gastrin stimulated by calcium), pancreatitis. **Psychic moans**: depression, cognitive dysfunction, lethargy, stupor, coma. **ECG**: shortened QT interval (calcium shortens phase 2 of cardiac action potential) — opposite of hypocalcemia. **Workup**: first check corrected calcium (add 0.8 mg/dL per 1 g/dL albumin below 4) or ionized calcium. Then PTH: if elevated → primary/tertiary HPT; if suppressed → malignancy workup (PTHrP, SPEP, imaging). Check PTHrP, vitamin D levels (25-OH and 1,25-OH), ACE level (sarcoid), SPEP.

Treatment by Severity

**Mild (10.5–12 mg/dL, asymptomatic)**: oral hydration, treat underlying cause. Monitor for worsening. **Moderate–severe (>12 or symptomatic)**: IV normal saline aggressive hydration (3–4 L in first few hours; furosemide only after adequate hydration to prevent pulmonary edema, NOT as first-line). **Bisphosphonates** (zoledronic acid or pamidronate): osteoclast inhibition — onset 24–48h, peak effect 2–4 days; drug of choice for malignancy-associated hypercalcemia. **Calcitonin**: fastest-acting (hours), but tachyphylaxis within 48h; useful as bridge until bisphosphonates kick in. **Corticosteroids**: for vitamin D-mediated hypercalcemia (sarcoid, lymphoma) — suppress macrophage 1α-hydroxylase. **Denosumab** (RANK-L inhibitor): useful when bisphosphonates fail. **Hemodialysis**: for severe hypercalcemia with renal failure. **Primary HPT management**: parathyroidectomy if symptomatic, Ca >1 mg/dL above normal, age <50, T-score ≤−2.5, 24h urine calcium >400 mg, or creatinine clearance <60.

Test yourself

Quick check — 3 questions

1. A 62-year-old woman with a 30-pack-year smoking history presents with fatigue, confusion, and constipation. Calcium is 13.8 mg/dL. PTH is <5 pg/mL (suppressed). What is the most likely cause and next best test?

2. What is the most appropriate initial treatment for a patient with symptomatic hypercalcemia of 14.2 mg/dL due to metastatic breast cancer?

3. A 45-year-old woman has incidentally discovered hypercalcemia of 11.2 mg/dL on routine labs. PTH is elevated at 95 pg/mL. She has no symptoms and her BMD T-score is −1.8. What is the appropriate management?

Frequently asked questions

How do I differentiate primary hyperparathyroidism from malignancy-related hypercalcemia?

PTH level is the key: primary HPT has elevated or inappropriately normal PTH with hypercalcemia. Malignancy suppresses PTH to near zero. Check PTHrP (elevated in humoral hypercalcemia of malignancy — squamous cell, RCC), 24h urine calcium, vitamin D levels, and SPEP. Primary HPT is usually chronic and asymptomatic; malignancy-related is acute, severe, and symptomatic.

Why should furosemide not be used first-line for hypercalcemia?

Loop diuretics can worsen hypercalcemia if the patient is volume-depleted by increasing proximal tubular calcium reabsorption. IV normal saline must be given first to ensure adequate volume status and promote urinary calcium excretion. Furosemide is only added after euvolemia is established and only if the patient is at risk for fluid overload.

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