Brittle Bones, Late Diagnosis

I received a call about 4 months ago from a family physician, who wanted me to perform a USG or CT guided biopsy for a mass in the anterior compartment of the right thigh in a 47-years old woman. He did not give me any more details and said the patient would get in touch with me.

I forgot about this, until a month later, when I was going through some histopathology reports of biopsies done by my ultrasonologist and chanced upon a report that described a hemangiopericytoma in the thigh with a comment saying that this was consistent with a phospaturic mesenchymal tumor.

Image

Fig. 1: Ultrasound shows the mass in the anterior compartment of the right thigh (red arrow) with the biopsy needle (blue arrow)

I called for more details and then realized that this was the same patient that the family physician, a month ago, had called about. Different people in our department do ultrasound and CT-guided biopsies and the patient went straight to the ultrasonologist, who in turn, went ahead and performed a core biopsy of the mass in the anterior compartment of the thigh (Fig. 1).

A phosphaturic mesenchymal tumor is a rare condition and typically secretes FGF-23 (fibroblastic growth factor) that produces osteomalacia. This combination is called oncogenic osteomalacia or tumor-induced osteomalacia (TIO).

I then asked the patient to get all the reports and details.

Image

Fig. 2: Radiograph shows an insufficiency fracture (arrow) of the base of the proximal right 3rd metatarsal bone.

Image

Fig. 3: Radiograph shows an insufficiency fracture (arrow) of the mid-left 5th metatarsal bone.

It had taken 5 years to get to this diagnosis. She started with an insufficiency fracture, five years ago, in the right 3rd metatarsal bone (Fig. 2), followed a month later by another fracture in the left 5th metatarsal bone (Fig. 3). She received symptomatic treatment and went from doctor to doctor with variable diagnoses of osteoporosis and perhaps osteomalacia.

This went on for 4 years, until one day, she was unable to get up from bed. She was admitted to a hospital and a skeletal survey showed fractures of the necks of both humeri (Fig. 5) and femurs (Fig. 6) with biconcave vertebrae (Fig. 7). Finally she received a diagnosis of osteomalacia and was worked up.

Her serum calcium was normal, vitamin D was normal, serum phosphorus was very low and her 24-hours urine phosphorus was elevated with a normal serum parathormone level and a raised serum alkaline phosphatase level. She did not fit into vitamin D related causes or phosphate deficiency conditions and what was left was a potential diagnosis of oncogenic osteomalacia.

Fig 4

Fig. 4: Radiographs of both shoulders show fractures (red arrows) of the necks of both humeri

Fig 5

Fig. 5: Radiograph of the bones of the pelvis and both hips show fractures (red arrows) of the necks of both femurs.

Lateral radiograph of the spine shows biconcave vertebrae

Fig. 6: Lateral radiograph of the spine shows biconcave vertebrae

Thus started the search for an FGF-secreting tumor that produces phosphaturia, hypophosphatemia and osteomalacia. A PET/CT then showed a mass with low FDG uptake in the anterior compartment of the thigh (Fig. 7), which was then biopsied. The common tumors that produce FGF are hemangiopericytoma, hemangioma, giant cell tumor and non-ossifying fibroma.

Contrast enhanced CT scan shows a hypervascular lesion (arrow) in the anterior compartment of right thigh, with mild FDG uptake (arrow) on the PET study.

Fig. 7: Contrast enhanced CT scan shows a hypervascular lesion (arrow) in the anterior compartment of right thigh, with mild FDG uptake (arrow) on the PET study.

She was operated and the tumor removed. Most patients show dramatic recovery of their phosphorus levels, but the skeletal changes and fractures take time to heal. The patient is slowly getting better symptomatically.

The most common reason for delayed diagnosis (in her case 5 years with an average time of 4.7 years from start of symptoms to final diagnosis) is due to lack of awareness and the inability to find the tumor.

This case was recently presented by our DNB resident Dr. Parang Sanghavi in the Teaching Files Case Presentation meeting in Mumbai, where it won the first prize in the 3rd year residentsā€™ category.

%d bloggers like this: