An interesting cause of hyponatremia

HOSP # WARD Red Cross Hospital Oncology ward
CONSULTANT   Dr Amith Ramcharan / Dr Jody Rusch DOB/AGE 11y Female

Abnormal Result

Persistent hyponatremia

2018 supracellar JPA (Astrocytoma)

Seizures – phenobarb.

Chemo @ 8 y of age.

Vincristin and Carboplatin administration

Craniospinal radiation – leptospinal

Presenting Complaint

Seizures – controlled with Phenobarbital

History

This is an 11 year old patient with a suprasellar JPA (Juvenile Pilocytic Astrocytoma). The tumour was diagnosed at 8y of age, upon which chemotherapy with Vincristine and Carboplatin was initiated. The pituitary was close to the area of radiation therapy as well.

Examination

The patient’s hydration status was normal and there was no cerebral edema.

Laboratory Investigations

2018 – Electrolytes relatively stable
2018-2019 – Hyponatremia and hypomagnesemia developing

The patient was found to have hypothyroidism and started on T4 replacement 50ug mane.

Other Investigations

Urine electrolytes on 23/02/2021:

  • Na 54 mM
  • K 31.3 mM
  • Cl 110 mM
  • Osmol 554 mOsmol
  • Fractional reabsorption of phosphate: 85%

Final Diagnosis

Unknown – but likely indicates a tubular loss of sodium due to the chemotherapeutic agent(s).

Take Home Message

Chemotherapeutic agents does cause tubulopathy.

TMP/GFR is likely a better indicator of renal phosphate handling than only fractional reabsorption of phosphate. This can be calculated mathematically or read from a nomogram.