What is the most appropriate next step in management for a 9-year-old child with gradually worsening bilateral leg pain, normal physical examination, adequate diet, and reduced outdoor activity?

Management of Bilateral Leg Pain in a 9-Year-Old with Reduced Outdoor Activity

The most appropriate next step is to prescribe vitamin D supplementation (with or without calcium) after considering the clinical presentation of gradually worsening bilateral leg pain, reduced outdoor activity, and fatigue—all consistent with vitamin D deficiency. 1

Rationale for Vitamin D Supplementation

Vitamin D supplementation (800–1000 IU vitamin D₃ daily) is the preferred first-line therapy for suspected deficiency in the absence of documented hypocalcemia, as it directly corrects the deficiency and enhances calcium absorption. 1 This child's presentation—bilateral leg pain, reduced outdoor activity, and fatigue after short distances—strongly suggests vitamin D deficiency, which commonly presents with these symptoms before overt skeletal changes become visible. 1

Why Not Sun Exposure Alone?

While sun exposure theoretically produces vitamin D, recent high-quality randomized controlled trials demonstrate that sun exposure recommendations are insufficient to overcome vitamin D deficiency in real-world settings:

• A 2020 Korean RCT showed that 30-60 minutes of sun exposure 3 times weekly increased serum 25(OH)D by only 0.9 ng/mL, while 800 IU daily supplementation increased it by 3.5 ng/mL. 2
• Another 2020 RCT found that sun exposure increased 25(OH)D by 2.2 ng/mL versus 8.5 ng/mL with 500 IU daily supplementation, with only 12% of sun exposure participants reaching adequate levels versus 54% with supplementation. 3
• A 2021 real-world study showed no significant increase in vitamin D levels with sun exposure advice, while 1,000 IU daily supplementation increased levels by 11 ng/mL. 4

These studies consistently demonstrate that oral supplementation is 3-4 times more effective than sun exposure recommendations for correcting vitamin D deficiency. 2, 3, 4

Why Not Orthopedic Referral?

Orthopedic referral should be postponed until metabolic causes have been ruled out; it is indicated only if significant limb deformities are present or if metabolic work-up is abnormal. 1 This child has a normal physical examination, making immediate orthopedic referral premature. 1

Clinical Algorithm

1. Initiate vitamin D supplementation immediately (800-1000 IU daily) based on the clinical presentation. 1

2. Consider baseline laboratory evaluation if symptoms are severe or persistent, including serum phosphate, alkaline phosphatase, 25-hydroxyvitamin D, and parathyroid hormone to rule out metabolic bone disorders like X-linked hypophosphatemia. 1

3. Reassess in 2-3 months: If symptoms persist despite adequate supplementation, evaluate for alternative metabolic bone disorders (e.g., X-linked hypophosphatemia characterized by low serum phosphate, elevated alkaline phosphatase, and elevated FGF23). 1

4. Refer to orthopedics or metabolic bone specialist only if: significant limb deformities develop, metabolic work-up is abnormal, or symptoms fail to improve with adequate vitamin D repletion. 1

Critical Pitfalls to Avoid

• Do not assume that a normal physical examination rules out vitamin D deficiency—biochemical abnormalities and symptoms precede visible skeletal findings. 1
• Do not rely solely on increased outdoor activity—compliance is poor and effectiveness is minimal compared to supplementation. 2, 3, 4
• Do not delay treatment while waiting for laboratory confirmation in a clinically suggestive case, as vitamin D supplementation is safe and addresses the most likely diagnosis. 1

Answer: D. Prescribe Calcium + vitamin D supplementation (though vitamin D alone would be sufficient if calcium intake is adequate through diet). 1