Rare Classroom: Tumor-Induced Osteomalacia

Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:

Tumor-Induced Osteomalacia

This rare disease is also known as oncogenic osteomalacia.

What is Tumor-Induced Osteomalacia?

  • A rare paraneoplastic form of renal phosphate wasting that results in severe hypophosphatemia, a defect in vitamin D metabolism, and osteomalacia
  • Symptoms usually nonspecific and often progressive. Can include bone pain, muscle weakness, fatigue and a softening of the bones
  • Prevalence of the disease is not known. Since the association between phosphate reabsorption and tumor was first made, about 300 cases of TIO have been reported in the literature worldwide
  • Treatment options include tumor resection surgery depending on the location. Phosphate supplements and calcitriol (vitamin D supplement) are other options.
  • Tumors can occur anywhere in the body making it often extremely difficult to diagnosis since tumors can be too small for detection by conventional radiological method​s.

How Do You Get It?

What Are The Symptoms?

  • Bone and muscle pain (especially in the ankles, legs, hips and back)​
  • Muscle weakness​
  • Reduced height​
  • Fatigue​
  • Osteomalacia (softening of the bones typically through a deficiency of vitamin D or calcium.)​
  • Multiple fractures (primarily in the ribs, vertebral bodies and femoral neck)​

How Is It Treated?

  • The goal of treatment is to cure TIO with resection of tumor or supplementation
  • Current treatment methods for TIO are tumor resection and phosphate supplements and active vitamin D supplements
  • Barriers to treatment include lack of knowledge which prolongs the length of time from onset of symptoms until diagnosis.
    • Symptoms presented are reminiscent of how patients would present advanced primary hyperparathyroidism
  • Health care team consists of rheumatologist, nephrologist and endocrinologist
  • Prognosis depends on detecting the tumor and resection with wide margin to insure complete removal, as recurrences have been reported. Typically benign in most of the cases. Symptoms disappear and the healing of the bones begin after resection. 
  • Follow-up should continue because delayed metastasis can occur as it was described in few cases.

Treatment for tumor-induced osteomalacia can be categorized into two different options.

  • Option 1: Resection (removal) of the tumor
    • Resection of the tumor (if it can be localized) with wide margins to ensure complete removal, is considered the “gold standard“ However it can be associated with considerable morbidity depending on the location
    • In some instances, the tumor recurs locally and in other, rare instances, tumors metastasize
    • Most patients feel better within days to weeks after removal. Bone healing starts immediately, but depending on the severity of the disease, it may take up to a year for a more significant clinical improvement to be seen
  • Option 2: Supplements and Medication
    • Phosphate supplements and calcitriol or alfacalcidol (vitamin D supplement) are given if the tumor cannot be located
    • Octreotide and cinacalcet are alternative forms of medical therapy​.

Where Can I Learn More???

  • Check out our cornerstone on this disease here.

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