Management of Elevated PTH with Low Vitamin D and Normal Calcium in a 78-Year-Old Female
The patient should be treated with vitamin D supplementation (ergocalciferol) to correct the vitamin D deficiency, with close monitoring of calcium and PTH levels. 1
Initial Assessment and Diagnosis
This patient presents with a classic picture of secondary hyperparathyroidism due to vitamin D deficiency:
- Elevated PTH: 7.8 pmol/L
- Low vitamin D: 23.9 ng/mL (below the target of 30 ng/mL)
- Normal calcium: 2.28 mmol/L
Key Considerations:
- The normocalcemia with elevated PTH and low vitamin D strongly suggests secondary hyperparathyroidism due to vitamin D deficiency rather than primary hyperparathyroidism
- In primary hyperparathyroidism with vitamin D deficiency, calcium levels can sometimes be normal despite elevated PTH 2
- Vitamin D deficiency is common in elderly patients and can exacerbate hyperparathyroidism
Treatment Plan
1. Vitamin D Supplementation
- Begin ergocalciferol (vitamin D2) supplementation based on the severity of deficiency 1
- For vitamin D levels between 15-30 ng/mL: Ergocalciferol 50,000 IU weekly for 8 weeks, then monthly
- Recheck 25-hydroxyvitamin D levels after 8 weeks of therapy
2. Monitoring Parameters
- Measure serum calcium and phosphorus every 3 months 1
- Monitor PTH levels after vitamin D repletion is achieved
- Annual reassessment of 25-hydroxyvitamin D levels once repleted
3. Safety Precautions
- If serum calcium exceeds 10.2 mg/dL (2.54 mmol/L), discontinue vitamin D therapy 1
- If serum phosphorus exceeds 4.6 mg/dL (1.49 mmol/L), consider phosphate binders or reducing vitamin D dose 1
- Avoid excessive vitamin D supplementation to prevent hypercalcemia, especially in patients with potential primary hyperparathyroidism 3
Differential Diagnosis Considerations
Primary vs. Secondary Hyperparathyroidism
- Primary hyperparathyroidism typically presents with hypercalcemia, but can present with normocalcemia when vitamin D deficiency is present 2, 4
- Secondary hyperparathyroidism due to vitamin D deficiency presents with normal calcium and elevated PTH
- Tertiary hyperparathyroidism is less likely given the patient's normal calcium
Evaluation for Primary Hyperparathyroidism
If PTH remains elevated after vitamin D repletion:
- Consider parathyroid imaging (ultrasound, sestamibi scan)
- Evaluate 24-hour urinary calcium excretion
- Consider bone mineral density testing
Clinical Pearls and Pitfalls
Important Considerations:
- Vitamin D supplementation in patients with primary hyperparathyroidism has been shown to be safe and can actually decrease PTH levels by 17% 5
- Vitamin D deficiency can mask hypercalcemia in primary hyperparathyroidism, leading to diagnostic uncertainty 4
- Vitamin D deficiency contributes to greater severity of hyperparathyroidism and bone disease 6
- Correcting vitamin D deficiency before parathyroidectomy (if needed later) is important to prevent post-operative hypocalcemia and hungry bone syndrome 4
Monitoring Response:
- Successful vitamin D repletion should lead to decreased PTH levels if secondary hyperparathyroidism
- If PTH remains elevated after adequate vitamin D repletion, further workup for primary hyperparathyroidism is warranted
- Vitamin D alone appears as effective as combined calcium/vitamin D treatment in restoring vitamin D levels in older patients 7
By following this approach, you can effectively manage this patient's condition while monitoring for any changes that might indicate primary rather than secondary hyperparathyroidism.