# Case Report: Phosphaturic mesenchymal tumor presenting solely as knee pain without hypophosphatemia

## TL;DR

A rare tumor causing bone pain typically involves low phosphate levels, but this case report describes a patient with knee pain only, without phosphate issues.

## Contribution

This case report highlights a unique presentation of phosphaturic mesenchymal tumor without hypophosphatemia or osteomalacia.

## Key findings

- The patient exhibited knee pain without hypophosphatemia or tumor-induced osteomalacia.
- Post-surgery follow-up showed complete resolution of knee swelling and pain.
- Imaging and biochemical tests one year post-surgery were normal.

## Abstract

Phosphaturic mesenchymal tumor (PMT) is a rare tumor disease that often leads to tumor-induced osteomalacia (TIO). The typical manifestations of this disease include hypophosphatemia and osteomalacia. The main symptom in most PMT patients is diffuse pain throughout the body. However, we report a PMT patient with typical histological features but without hypophosphatemia and TIO. This patient only presented with pain in the right knee joint. At 6 months and 1 year after surgery, follow-up revealed that the patient’s swelling and pain in the right knee joint had disappeared. Moreover, the imaging and biochemical examinations conducted at the local hospital showed normal results.