✅ Model Answer:
• Diagnosis: Primary hyperparathyroidism (elevated Ca, low P, elevated PTH, hypercalciuria). In children, most common cause is a solitary parathyroid adenoma (can be part of MEN1 syndrome).
• Any other test: CaSR gene (to differentiate from FHH – familial hypocalciuric hypercalcemia); 1,25-(OH)₂D; MEN1 genetic testing; neck ultrasound or sestamibi scan for localization; renal ultrasound for nephrolithiasis.
• What to do next: Bilateral neck exploration with subtotal (3-3.5 gland) parathyroidectomy. Preoperative: IV hydration, bisphosphonates if severe hypercalcemia.
• Follow-up plan: Monitor for hungry bone syndrome post-op – check Ca, P, Mg daily; give IV/oral calcium and calcitriol as needed. Long-term: monitor calcium, PTH annually. Screen for MEN1-associated tumors (pituitary, pancreas, parathyroid).

✅ Model Answer:
• Solitary parathyroid adenoma: Accounts for ~80-85% of cases in children (most common).
• Parathyroid hyperplasia: ~10-15% (especially in MEN1 and MEN2A).
• Parathyroid carcinoma: Rare in children (<1%).
• MEN1 syndrome: Responsible for ~20-30% of pediatric primary hyperparathyroidism (younger age at presentation, multiglandular disease).
• MEN2A: Also associated with hyperparathyroidism (but less common than MEN1).
• Ectopic parathyroid adenoma: In mediastinum, thymus, or carotid sheath (rare).

✅ Model Answer:
• Classic symptoms (mnemonic: "stones, bones, abdominal groans, psychic moans"):
- Stones: Nephrolithiasis (kidney stones) – recurrent abdominal pain, hematuria, dysuria.
- Bones: Bone pain, fractures, osteopenia, osteoporosis, subperiosteal bone resorption.
- Abdominal groans: Abdominal pain, constipation, nausea, vomiting, peptic ulcer disease, pancreatitis.
- Psychic moans: Depression, fatigue, confusion, memory loss.
• Other features:
- Polyuria, polydipsia: Due to hypercalcemia-induced nephrogenic diabetes insipidus.
- Muscle weakness.
- Hypertension.
- Short stature (if chronic).
• Asymptomatic: Many children are asymptomatic (detected incidentally on routine blood work).

✅ Model Answer:
• Biochemical tests:
- Serum calcium: Elevated (>10.5 mg/dL).
- Ionized calcium: Elevated.
- Serum phosphorus: Low (due to PTH-mediated renal phosphate wasting).
- PTH: Elevated or inappropriately normal (in the setting of hypercalcemia).
- 25-OH vitamin D: Normal or low (if vitamin D deficiency coexists).
- 1,25-(OH)₂D: Elevated (PTH stimulates 1α-hydroxylase).
- 24-hour urine calcium: Elevated (>4 mg/kg/day).
- Ca/Cr clearance ratio: >0.01 (differentiates from FHH where ratio <0.01).
• Imaging:
- Neck ultrasound: First-line to localize adenoma.
- Sestamibi scan (parathyroid scintigraphy): More sensitive for ectopic or small adenomas.
- 4D CT scan: High-resolution localization.
• Genetic testing:
- MEN1, RET, CaSR: If family history or syndromic features.

✅ Model Answer:
• Definitive treatment: Parathyroidectomy
- Approach: Bilateral neck exploration (or focused surgery if adenoma localized).
- Extent: Subtotal (3-3.5 gland) parathyroidectomy for hyperplasia; single adenoma removal for adenoma.
- Intraoperative PTH monitoring: To confirm complete removal (PTH drops by >50% at 10 minutes).
• Preoperative management:
- IV hydration: To correct dehydration and promote calcium excretion.
- Bisphosphonates: For severe hypercalcemia (pamidronate 1 mg/kg IV).
- Calcimimetics: Cinacalcet (rarely used in children).
• Medical management (for asymptomatic or non-surgical candidates):
- Hydration, low calcium diet, avoid thiazides.
- Bisphosphonates.

✅ Model Answer:
• Renal complications:
- Nephrolithiasis: Calcium oxalate or calcium phosphate stones.
- Nephrocalcinosis: Calcium deposition in renal tubules.
- Chronic kidney disease: Progressive renal impairment.
- Polyuria, polydipsia.
• Skeletal complications:
- Osteitis fibrosa cystica: Bone pain, brown tumors, fractures.
- Osteoporosis, osteopenia.
- Subperiosteal bone resorption: On X-ray (classic in phalanges).
• Gastrointestinal:
- Pancreatitis: Severe, recurrent.
- Peptic ulcer disease.
- Constipation.
• Neuropsychiatric:
- Depression, fatigue, confusion, cognitive impairment.
• Cardiovascular:
- Hypertension, arrhythmias (shortened QT interval).
• Hypercalcemic crisis: Life-threatening (Ca >14 mg/dL) – causes dehydration, confusion, coma, arrhythmias.

✅ Model Answer:
• Prognosis:
- Excellent with successful parathyroidectomy.
- Complete resolution: Calcium and PTH normalize; bone density improves.
- Hungry bone syndrome: Post-operative hypocalcemia (due to rapid bone remineralization) – requires IV/oral calcium and calcitriol (usually temporary).
- Persistent or recurrent hyperparathyroidism: In multiglandular disease or MEN1 (requires re-exploration).
- MEN1: Requires lifelong surveillance for other tumors (pituitary, pancreas, thymus).
• Long-term follow-up:
- Monitor calcium, PTH: Annually.
- Bone density (DEXA): If osteopenia/osteoporosis.
- Renal function: Creatinine, urine calcium.
- MEN1 screening: Annual prolactin, IGF-1, glucose, pancreatic imaging.
- Genetic counseling: For MEN1 (autosomal dominant, 50% risk).

✅ Model Answer:
• Primary hyperparathyroidism (PHPT):
- Cause: Parathyroid adenoma or hyperplasia.
- Calcium: Elevated.
- Phosphorus: Low.
- PTH: Elevated or inappropriately normal.
- Urine calcium: Elevated (>4 mg/kg/day).
- Ca/Cr clearance ratio: >0.01.
- Treatment: Parathyroidectomy.
- Symptoms: Nephrolithiasis, bone pain, pancreatitis.
• Familial hypocalciuric hypercalcemia (FHH):
- Cause: CaSR gene mutation (loss-of-function) → PTH set point reset.
- Calcium: Mildly elevated (usually <11.5 mg/dL).
- Phosphorus: Normal (unlike PHPT).
- PTH: Normal or mildly elevated.
- Urine calcium: Low (<4 mg/kg/day).
- Ca/Cr clearance ratio: <0.01.
- Treatment: No treatment (benign).
- Symptoms: Usually asymptomatic; incidental finding.
- Inheritance: Autosomal dominant.