Question

A child with rachitic changes in limbs, which was not responding to Vitamin D. Investigations done shows
Calcium- 9.5mg/dl, Phosphorous- 1.6 mg/dl, ALP- 814 IU, Sr. PTH- 24.2.Sr. Electrolytes, Creatinine and blood gases- normal.Diagnosis?

• A. Vitamin D dependent rickets type 1
• B. Vitamin D dependent rickets type 2
• C. Hypophosphatemic rickets
• D. Chronic renal failure

Answer 1

The Correct Option is C

The clinical presentation and laboratory findings of the child indicate the presence of a type of rickets that is not responsive to Vitamin D therapy, showing specific biochemical abnormalities.

Key laboratory results to note:

• Calcium: 9.5 mg/dL (within normal range)
• Phosphorous: 1.6 mg/dL (hypophosphatemia)
• Alkaline Phosphatase (ALP): 814 IU (elevated)
• Serum Parathyroid Hormone (PTH): 24.2 (within normal range)
• Normal serum electrolytes, creatinine, and blood gases

Let us examine the differential diagnosis:

1. Vitamin D Dependent Rickets Type 1: Characterized by defective conversion of calcidiol to calcitriol, resulting in low serum calcium and phosphorus, elevated ALP, and increased PTH levels. The child’s calcium and PTH levels are normal, making this diagnosis unlikely.
2. Vitamin D Dependent Rickets Type 2: Caused by target organ resistance to calcitriol, typically showing low calcium, low phosphorus, and elevated PTH levels. Again, normal calcium and PTH levels rule this out.
3. Hypophosphatemic Rickets: Typically presents with low serum phosphorus, normal to low calcium, elevated ALP, and unaffected PTH. This condition is often resistant to standard Vitamin D therapy, matching the clinical scenario of the child.
4. Chronic Renal Failure: Would lead to metabolic disturbances including elevated creatinine, which is not present here.

In conclusion, the child’s symptoms and laboratory findings are most consistent with Hypophosphatemic rickets, characterized by low phosphate levels, normal serum calcium, and resistance to Vitamin D treatment.