Who stole the salt: an atypical cause of severe hyponatraemia — ASN Events
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Who stole the salt: an atypical cause of severe hyponatraemia (#433)

Abidev Kuhasri 1 , Mohammad Raiyan Khan 1 , Namson S Lau 1 2
  1. Department of Diabetes & Endocrinology, Liverpool Hospital, Liverpool, NSW, Australia
  2. South West Sydney Clinical School, UNSW Medicine, Sydney, NSW, Australia

Objectives:

Acute Intermittent Porphyria (AIP) is a rare genetic disorder of haem production, resulting in accumulation of its precursor, porphyrins. We describe a newly diagnosed case, presenting with seizures due to acute severe hyponatraemia from their acute intermittent porphyria.

Summary:

A 20-year-old female university student presented with a 7-day history of right iliac fossa abdominal pain, nausea and vomiting. Her background was significant for a history of depression, medicated with Mirtazapine. After an initial presumed diagnosis of urinary tract infection, the patient deteriorated with a new onset severe headache and recurrent seizures. Her initial neuroimaging and lumbar puncture were unremarkable, however the seizure work-up revealed new severe hyponatraemia to 103mmol/L. The patient was clinically euvolemic with a serum osmolality of 218mmol/L, urine Na of 150mmol/L and urine osmolality of 476mmol/L and in the absence of thyroid or adrenal diseases, this was presumed to be due to Syndrome of Inappropriate Antidiuretic Hormone (SIADH) with acute treatment of hypertonic saline.

As part of the SIADH workup, serum, urine and faecal porphyrins were completed and returned significantly elevated after a prolonged turnaround time. The pattern of elevation was consistent with AIP. 

The patient was treated acutely with Hemin, to replenish her haem stores, and has subsequently had four further flares requiring treatment. She remains under consideration for an RNA therapeutic, Givosiran, for chronic treatment. However, this is not currently PBS-listed and would need be accessed under compassionate access.

Conclusion:

The diagnosis of AIP ultimately explained her constellation of symptoms including severe abdominal pain, hyponatraemia, seizures and depression. Hyponatraemia is a common manifestation of porphyria flares, occurring in 25-60% of cases. This highlights that contrary to Occam’s razor; rare conditions may be the cause of very common presentations; here the severity of hyponatraemia was the clue that this may not be SIADH.