Endocrine Abstracts

Case History: A 27 year-old lady, seven weeks gestation presented to ED during her second pregnancy with abdominal pain, vomiting, constipation and hyponatraemia (Na = 114mmol/l). She had attended twice earlier during her pregnancy with presumed hyperemesis gravidarum. Because urinary sodium was elevated at 181mmol/l, dehydration was deemed unlikely and she was initially treated as SIADH with 1.2L fluid restriction and 2.7% 200mls of hypertonic saline. Sertraline was held. Repeat sodium next day had dropped further to 112mmol/l, following which a further 2.7% NS bolus was given. Sodium remained refractory to this, despite being followed up by a 500ml 1.8% saline infusion at 50mls/hr. An abdominal ultrasound was obtained for persistent generalised abdominal pain which was unremarkable. Laxatives were given as bowels hadn’t opened in more than one week. Starvation ketosis without acidosis was noted and dietetic input was requested. Intravenous Pabrinex was given. A porphyria screen was requested at this stage, which was suggestive of acute intermittent porphyria. Biochemistry was consulted and the patient was sent to HDU for haem arginate infusion 3 mg/kg daily for 4 days. Fluid restriction was lifted and the patient was given 0.9% NS for the remainder of her admission and sodium normalised. No neurological or respiratory deficit was noted during her admission.

Investigations: Abdominal Ultrasound: Biliary sludge Chest X-ray: Normal

Results and Treatment: Osmolality(serum)= 237 mOsm/kg [Ref.275-295 (mOsm/kg)] Osmolality(urine)= 587 mOsm/kg Urea = 1.4mmol/l (2.5-7.8mmol/l) Urine(Na)= 181mmol/l Ketones= 3.6mmol/l Urine porphobilinogen= 559.8 (0-10.7 umol/l) PBG/Creatinine= 64 (<1.5umol/mmol) Porphyrin/Creatinine= 796 (0-40nmol/mmol)

Conclusion and Points for Discussion: Acute intermittent porphyria is rare autosomal dominant condition characterised by partial deficiency of the enzyme hydroxymethylbilane synthase, which results in the accumulation of porphyrin precursors in the body. It can be triggered by various factors such as pregnancy and other hormonal changes, fasting, infections, medications and alcohol consumption. It can present with abdominal pain, constipation, tachycardia, hypertension, behavioural changes, seizures and peripheral neuropathy or paralysis. Drugs that may precipitate acute intermittent porphyria include: anabolic steroids, antidepressants (MAOI, TCA), hormonal contraceptives, antifungals, sulphonylureas and taxanes. A safe drug list can be found on the UKPMIS website. Although acute intermittent porphyria is a very rare disorder, this case highlights the need to consider porphyria as a differential diagnosis in a patient with abdominal pain and refractory or unexplained hyponatraemia.