Genetically Confirmed Hyperphosphatemic Tumoral Calcinosis: A Case Report

Familial hyperphosphatemic tumoral calcinosis is a rare autosomal recessive disorder characterized by periarticular deposition of calcium-phosphate material in soft tissues.We describe the case of a 15-year-old Gabonese patient presenting with multifocal involvement of the left hip, elbow, and shoulder, evolving for four years.The condition was initially misdiagnosed as a giant cell tumor of soft tissues, and a definitive diagnosis was established by histological examination after excision of the elbow mass.Biological workup revealed isolated hyperphosphatemia at 66.0 mg/L and 25-hydroxyvitamin D deficiency at 16.7 ng/mL, with an otherwise unremarkable laboratory profile.Genetic testing identified a homozygous pathogenic variant in the GALNT3 gene (NM_004482.4:c.484C>T,p.Arg162Ter), confirming familial hyperphosphatemic tumoral calcinosis type 1. MRI of the left shoulder demonstrated multiple calcified nodules within the subcoracoid bursa extending into the surrounding musculature.After histological and genetic confirmation of the diagnosis, management consisted of surgical excision, combined with phosphate-lowering therapy and cautious vitamin D supplementation under biochemical monitoring.This case is particularly noteworthy for its multifocal nature, young age of onset, and initial diagnostic delay.