Which condition is a paraneoplastic cause of renal phosphate wasting leading to osteomalacia?

Which condition is a paraneoplastic cause of renal phosphate wasting leading to osteomalacia?

• A. Tumor-induced osteomalacia (TIO).
• B. X-linked hypophosphatemic rickets.
• C. Autosomal dominant hypophosphatemic rickets.
• D. Vitamin D deficiency.

Answer: (A)

Renal phosphate wasting with osteomalacia caused by a tumor is the classic paraneoplastic syndrome, driven by tumors that secrete phosphatonins such as FGF23. This excess FGF23 acts on the kidney to reduce phosphate reabsorption in the proximal tubule and suppresses 1α-hydroxylase, leading to low or inappropriately normal calcitriol. The result is hypophosphatemia with osteomalacia due to impaired phosphate availability for bone mineralization. Tumor-induced osteomalacia is resolved when the tumor is removed, after which phosphate handling and vitamin D activation improve. Inherited hypophosphatemic conditions like X‑linked or autosomal dominant forms involve genetic mutations causing phosphate wasting but are not driven by a tumor produce a paraneoplastic effect. Vitamin D deficiency causes osteomalacia through low intestinal absorption of calcium and phosphate rather than tumor-driven renal phosphate wasting.

Renal phosphate wasting with osteomalacia caused by a tumor is the classic paraneoplastic syndrome, driven by tumors that secrete phosphatonins such as FGF23. This excess FGF23 acts on the kidney to reduce phosphate reabsorption in the proximal tubule and suppresses 1α-hydroxylase, leading to low or inappropriately normal calcitriol. The result is hypophosphatemia with osteomalacia due to impaired phosphate availability for bone mineralization. Tumor-induced osteomalacia is resolved when the tumor is removed, after which phosphate handling and vitamin D activation improve.

Inherited hypophosphatemic conditions like X‑linked or autosomal dominant forms involve genetic mutations causing phosphate wasting but are not driven by a tumor produce a paraneoplastic effect. Vitamin D deficiency causes osteomalacia through low intestinal absorption of calcium and phosphate rather than tumor-driven renal phosphate wasting.