What is the management for an 11-year-old with symptoms of tetany and low Parathyroid Hormone (PTH) levels after a short febrile illness, despite having normal calcium and magnesium levels?

Management of Post-Febrile Hypoparathyroidism with Tetany in an 11-Year-Old

This child requires immediate intravenous calcium gluconate infusion to treat symptomatic hypocalcemia with tetany, followed by oral calcium supplementation and active vitamin D therapy (calcitriol) once stabilized, as this represents acute hypoparathyroidism triggered by a viral illness.

Immediate Emergency Management

Initiate IV calcium gluconate immediately for symptomatic tetany with positive Chvostek's and Trousseau's signs, even though serum calcium appears "normal" on laboratory testing 1, 2. The presence of clinical tetany indicates functional hypocalcemia requiring urgent treatment 3.

• Administer calcium gluconate 1-2 mg elemental calcium per kilogram body weight per hour via continuous infusion, adjusting to maintain ionized calcium in the normal range (1.15-1.36 mmol/L or 4.6-5.4 mg/dL) 1
• A 10-mL ampule of 10% calcium gluconate contains 90 mg of elemental calcium 1
• Monitor ionized calcium levels every 4-6 hours initially until symptoms resolve and levels stabilize 1

Critical Diagnostic Consideration

The "normal" total calcium may be misleading—you must obtain ionized calcium levels to assess true calcium status, as total calcium can be falsely normal due to protein binding variations 2, 3. Low PTH with tetany indicates the functional calcium is insufficient despite laboratory values 4.

Verify Magnesium Status

Recheck magnesium levels urgently despite initial normal results, as hypomagnesemia can cause both PTH suppression and peripheral PTH resistance, leading to refractory hypocalcemia 5.

• If magnesium is <1.4 mg/dL, supplement with IV or oral magnesium immediately, as hypocalcemia will not resolve without correcting magnesium deficiency first 5
• Magnesium depletion causes dual effects: initial PTH stimulation followed by inhibition as hypomagnesemia worsens 5

Transition to Oral Therapy

Once tetany resolves and the patient can take oral medications:

• Calcium carbonate 1-2 grams three times daily (total elemental calcium intake should not exceed 2,000 mg/day) 1
• Calcitriol 0.25-0.5 mcg daily or twice daily to enhance intestinal calcium absorption 1
• The evening dose of calcitriol may help prevent excessive calcium absorption after meals 1

Monitor serum calcium and phosphorus every 2 weeks for the first month, then monthly thereafter 1. Adjust calcitriol dose to maintain calcium in the low-normal range (8.4-9.5 mg/dL) 1.

Understanding Post-Viral Hypoparathyroidism

This presentation is consistent with transient hypoparathyroidism following viral infection 4. The proposed mechanisms include:

• Direct viral interaction with parathyroid gland tissue 4
• Inflammatory cytokine-mediated PTH resistance 4
• Viral-induced parathyroid dysfunction 4

The fact that calcium and magnesium appear "normal" on initial testing but the child has tetany suggests either:

1. Ionized calcium is actually low (must be measured directly) 3, 4
2. Rapid shifts in calcium homeostasis that laboratory values haven't captured 4
3. Peripheral PTH resistance from the inflammatory state 4

Monitoring and Follow-Up

• Repeat PTH levels in 2-4 weeks to determine if hypoparathyroidism is transient or persistent 6
• If PTH remains suppressed beyond 6 months, consider this permanent hypoparathyroidism requiring lifelong therapy 6
• Screen for basal ganglia calcification with head CT if symptoms persist or neurological signs develop, as chronic hypocalcemia can cause Fahr's syndrome 6

Common Pitfalls to Avoid

Do not rely solely on total calcium levels—ionized calcium is the physiologically active form and must be measured in symptomatic patients 2, 3. Total calcium can be falsely reassuring due to albumin binding 2.

Do not start vitamin D supplementation before correcting hypocalcemia—native vitamin D (cholecalciferol/ergocalciferol) takes 15-25 days to work and will not address the acute crisis 7. Use active vitamin D (calcitriol) instead 1.

Do not overlook magnesium deficiency—even "normal" magnesium should be rechecked, as it's essential for PTH secretion and action 5. Calcium repletion will fail if magnesium is depleted 5.

Avoid excessive calcium supplementation (>2,000 mg/day total intake) as this increases risk of nephrocalcinosis and hypercalciuria 1.