Osteitis deformans in neoplastic diseases, unsp lower leg

This diagnosis code signifies Paget's disease of bone occurring in the context of a neoplastic process, specifically affecting an unspecified lower leg. It describes a chronic bone remodeling disorder characterized by localized areas of increased bone turnover, leading to enlarged and weakened bones, when a malignancy is also present.

Use this code when documentation clearly indicates a diagnosis of Paget's disease of bone in the lower leg (e.g., tibia, fibula, ankle) and there is an associated neoplastic disease. The physician's notes should explicitly link the osteitis deformans to a co-existing malignancy, even if the malignancy is not directly causing the Paget's.

• Ensure the documentation specifies "unspecified lower leg" if the laterality (right/left) is not documented.
• Always code the underlying neoplastic disease first, as this code indicates a manifestation in neoplastic diseases.
• Distinguish from Paget's disease without an associated neoplasm (M88.-) and pathological fractures due to neoplasm (M84.5-).