Oncogenic osteomalacia secondary to phosphaturic mesenchymal tumour

Case contributed by Dr Harshad Arvind Vanjare


A middle aged lady presented with progressive generalised bone pain for 6 years and weakness for 2 years. At presentation she required support for walking.

Patient Data

Age: 45 years
Gender: Female

Frontal chest radiograph showing diffuse osteopenia

Annotated image

Magnified image of left femoral neck

Left femur neck with osteopenia, coarse trabeculations, thinning of cortex with presence of looser zone

Bone scan demonstrating increased tracer uptake in multiple ribs and vertebral bodies suggestive of multiple fractures. 

Increased uptake seen in multiple large joints. 

She was also found to have hypophosphatemia. Her serum calcium level was normal.


  • middle-aged woman
  • progressive bone pains with difficulty in walking
  • on imaging, severe osteopenia with multiple fractures
  • on blood investigations, hypophosphatemia

Provisional diagnosis:

  • adult-onset hypophosphatemic osteomalacia

The patient went on to be evaluated to try and ascertain the underlying cause. Workup included vitamin D deficiency/resistance, renal tubular acidosis and malabsorption all of which were negative. 

To evaluated for a paraneoplastic cause and blood pool scintigraphy was done. 

Nuclear medicine

Blood pool scintigraphy

Blood pool scintigraphy demonstrating pooling of tracer in the region of right anterior skull base. 


CT was done to look for any obvious anterior skull base abnormality

CT scan did not demonstrate any abnormality in the anterior skull base region.

In addition, nasal endoscopy also did not show any lesion. 

The patient was started on phosphate, calcium and vitamin D supplementation and requested to follow up in the outpatient department. 


Patient presented after 2 years with inability to walk

Fractures involving bilateral femoral necks.


Underwent bilateral hip replacement

Patient underwent bilateral hip replacement. 

She continued supplementation with phosphate and calcium. 

Unfortunately, the patient was lost to follow up for 6 years. At presentation, she was now predominantly bed bound with significant bone pain and depressed mood.  

She was found to be hypophosphatemic in spite of supplementation.

Nuclear medicine

Blood pool scintigraphy was repeated

Compared to the previous 'blood pool scintigraphy' done 8 years ago, the present study demonstrated increased tracer pooling the region of anterior skull base. 

MRI scan was done for further evaluation. 

MRI brain shows a well defined lobulated, solid cystic mass in the left basifrontal region with extension into the olfactory groove. There is surrounding mass effect with midline shift to the right. 

Case Discussion

At this stage the differentials considered were:

  1. haemangiopericytoma
  2. esthesioneuroblastoma
  3. phosphaturic mesenchymal tumour

The patient underwent left frontal craniotomy and total excision of the left anterior skull base mass. 


phosphaturic mesenchymal tumour, mixed connective tissue type



Oncogenic osteomalacia or tumour induced osteomalacia, is an acquired para-neoplastic syndrome.

Cases typically are diagnosed in 6th decade of life.

Tumours that can lead to this syndrome are classified histologically as:

  1. phosphaturic mesenchymal tumours with mixed connective tissue (70 -80%)
  2. osteoblastoma like tumours
  3. ossifying fibrous like tumours
  4. nonossifying fibrous like tumours

These tumours are often small in size and difficult to localize. The average time between the onset of symptoms and tumour localization is approximately 7 years.

These tumours often express somatostatin receptors. Therefore, scintigraphy using somatostatin analogue can be used for tumour localisation.

Cases can also have elevated serum Fibroblast Growth Factor 23 (FGF-23) levels which can be used for diagnosis or to assess disease progression. 

FDG-PET scan is increasingly been used for tumour localisation.


Tumour resection is the preferred treatment option.

Post-surgery FGF-23 levels fall off drastically.

Serum phosphate and 1,25-dihydroxy vitamin D levels return to normal levels within days after tumour resection.

Long-term skeletal changes reverse within months.



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Case information

rID: 58373
Case created: 14th Feb 2018
Last edited: 24th Feb 2018
Inclusion in quiz mode: Included

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