Continuous effect with long-term safety in zoledronic acid therapy for polyostotic fibrous dysplasia with severe bone destruction.

Polyostotic fibrous dysplasia (PFD) is a rare non-inherited genetic disorder characterized by osteolytic lesions in multiple bones causing bone pain, deformity, and pathological fracture. As an anti-osteolytic agent, the new generation bisphosphonate zoledronic acid (ZOL) restricts lesion progression by inhibiting osteoclastic activity. Although ZOL is more effective than pamidronate, its efficacy and safety in long-term therapy in PFD is unknown. We report a case of PFD advanced to extensive bone destruction in the skull and ribs and evaluate the efficacy and long-term safety of early first-line ZOL in PFD with severe bone disease, recommending possible future treatments. The annual infusion of 5 mg ZOL was intravenously administered, cumulatively 20 mg over four courses, with oral supplementation of calcium, vitamin D, and potassium. No long-term use side effect was observed, and mild transient symptoms were easily resolved. Significant radiological improvement was seen in filling of destroyed bone and cortical thickening. ZOL decreased both serum collagen type 1 cross-linked C-telopeptide and type 1 procollagen N-terminal (P1NP) from extremely high baseline levels. An unexpected direct increase in P1NP after long-term therapy could indicate discontinuation of ZOL to observe its prolonged effect. Early first-line ZOL therapy is effective in PFD with severe bone destruction and is safe for long-term therapy. The use of bisphosphonates in FD remains off-label, and regular monitoring is highly advised.