30 Jun 2022

11/23/20: Metastatic Adenocarcinoma with Tumor Induced Osteomalacia

PGY3 Julian McLain presented a case of a 60 year old female with history of seropositive rheumatoid arthritis and uterine leiomyomas who presents with 5 days of progressive bilateral leg swelling and decreased urine output.  She also has noted reduced oral intake due to feeling “uncomfortable” when she eats quickly followed by the need to move her bowels.  Denies any abdominal/pelvic pain or vaginal bleeding and has been post-menopausal for the last 6 years.  Home medications include ibuprofen 400mg PRN pain, Famotidine 20mg qday, Acetaminophen 1g PRN pain and “natural remedies”.  Family history significant for brother with renal cancer and mother with CKD.  Denies any history of alcohol/tobacco/drug use.

Vitals: T 36.8, HR 114, RR 20, BP 113/78, O2 sat 98% on RA

Physical Exam significant for cachectic Hispanic female, resting comfortably in bed, tachycardic but regular, no elevated JVD, normal pulmonary exam, +hepatosplenomegaly, firm nontender lower abdominal mass and 2+ bilateral lower extremity edema up to the knees.

CBC: WBC 16.1> Hb 11/Hct 34 <Plt 474 (MCV 90, RDW 20.6%)


Na 114/K 5.3/Cl 76/HCO3 14/BUN 29/Cr 0.49 <Glucose 78

ALP 388>T.protein 6.1/Albumin 3.1/AST 241/ALT 50/Tbili 7.4/Dbili 6.0

Ca 9.9, Mg 2.1, Phos 1.2

Coags: PT 18.3, INR 1.53

Infectious workup done with negative Bcx, UA, UCx, and Procalcitonin.

With the abdominal exam findings, imaging was performed with findings of innumerable hepatic masses and enlarged, multilobuated leiomyomatous uterus:

Given the hyponatremia, hypercalcemia and persistent hypophosphatemia, a renal workup was done:

  • UA: trace protein, trace ketones, moderate bili and small leuks (WBC 4-10/HPF)
  • Sosm: 242 mOsm/kg (normal 275 – 295)
  • Uosm: 369 mOsm/kg
  • Una: <20 mmol/L
  • Upotassium: 36 mmol/L
  • Uchloride: 58 mg/dL
  • Ucr: 58 mg/dL
  • Uurea: 630 mg/dL
  • Uuric acid: 78.5 mg/dL
  • Uphosphorous: 99.1 mg/dL (normal: 0.97 –  1.45)
  • Ucalcium: 2.5 mg/dL
  • PTH: 6 (normal: 15 – 65)
  • Vit D 25 OH: <5 (normal 30 – 100)
  • Vit D 1, 25 OH: <8 (normal 18 – 72)

Given the results from the renal workup and persistent phosphorous renal wasting, a FGF23 level was sent and resulted elevated at 4518 (normal <180).

Biopsy was performed on one of the hepatic lesions, resulting in metastatic adenocarcinoma, likely origin is colorectal.

Treatment: Nephrology was immediately consulted and started the patient on salt tabs, diuretics, demeclocycline along with aggressive IV PO4 repletion.  Once metastatic adenocarcinoma was confirmed via biopsy, the patient was set up with oncology for outpatient follow-up and patient was discharged.

Teaching points:

  1. Treatment of FGF23 tumor induced osteomalacia: find the tumor.  Surgically remove the tumor if able.  If unable to fully resect the tumor, vit-D 1,25 and phosphate repletion and anti-FGF23 monoclonal antibodies (Burosumab).

Phosphate Homeostasis

Workup of hypophosphatemia


Minisola, S. et al. (2017) Tumour-induced osteomalacia. Nat. Rev. Dis. Primers doi:10.1038/nrdp.2017.44

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