Working Diagnosis:
X-Linked Hypophosphatemic Rickets (XLH)

Treatment:
Per the family's preference, the patient had been receiving oral phosphate supplementation and calcitriol, managed by Pediatric Endocrinology with periodic adjustments based on lab results. The family was educated on medication adherence for optimal management. The patient also underwent bilateral epiphysiodesis of the distal femur and proximal tibia, managed by Orthopedic Surgery.

Outcome:
Over the past year, the patient has remained healthy, with no major concerns except for a dental issue. She has resumed sports participation, including basketball, archery, and soccer, and is active with biking, swimming, and playing with friends. She continues to be managed by Pediatric Endocrinology and Orthopedics, with regular follow-up for bone health, growth, and medication adjustments.

Author's Comments:
This case highlights the importance of maintaining a broad differential when evaluating chronic joint pain in pediatric athletes, especially when symptoms do not align with common overuse injuries. X-linked hypophosphatemic rickets (XLH) can mimic more common biomechanical or developmental conditions, yet has systemic implications that require early recognition and multidisciplinary management. For sports medicine providers, this case reinforces the value of careful physical exam findings, such as genu valgum and gait changes, and lab interpretation in uncovering rare metabolic bone diseases. Early diagnosis and coordination with endocrinology and orthopedics allowed this patient to resume sports and improve function.

Editor's Comments:
This case presents a compelling and instructive clinical scenario. The authors offer several valuable insights, particularly regarding diagnostic "pearls" that merit emphasis. While common presentations often align with familiar patterns--when we hear hooves, it is typically a horse--it is the role of the astute clinician to recognize when elements of the history or physical examination deviate from the expected illness or injury script. In this case, the severity of the patient's pain, functional limitations, abnormal gait, and inability to run were key indicators that warranted further investigation.

Two additional points are worth highlighting. First, although the basic metabolic panel and vitamin D levels were unremarkable, ordering serum phosphorus and alkaline phosphatase can provide important diagnostic clues when evaluating bone pain and overall bone health. Second, it is notable that the MRI findings were not particularly contributory in this case, underscoring the importance of integrating clinical judgment with imaging and laboratory data.

References:
Kamenicky P, Beck-Peccoz P, Linglart A, et al. X-linked hypophosphataemia. Lancet. 2024;404(10455):887-901. doi:10.1016/S0140-6736(24)00000-0

Carpenter TO, Imel EA, Holm IA, Jan de Beur SM, Insogna KL. A clinician's guide to X-linked hypophosphatemia. J Bone Miner Res. 2011;26(7):1381-1388. doi:10.1002/jbmr.340

Beck-Nielsen SS, Mughal Z, Haffner D, et al. FGF23 and its role in XLH-related morbidity. Orphanet J Rare Dis. 2019;14(1):58. doi:10.1186/s13023-019-1013-5

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