Endocrine Abstracts (2019) 62 P05 | DOI: 10.1530/endoabs.62.P05

A rare cause of hyponatraemia

Usman Javaid, Yaasir Mamoojee, Nicola Leech & Andy James

Department of Endocrinology, The Royal Victoria infirmary, Newcastle Hospitals NHS Foundation Trust, Newcastle-upon-Tyne, UK.

Case history: We describe a case of 35 year old female who presented with abdominal pain, nausea and lower backache. She was initially treated with Trimethoprim for a urinary tract infection. 5 days later, she re-attended hospital with feeling more unwell, ongoing lower abdominal pain and vomiting. On examination, she was haemodynamically stable. She had suprapubic tenderness on abdominal palpation, and the rest of her systemic examination was normal.

Investigations: Biochemistry showed significant hyponatraemia of 122 mmol/l. Her inflammatory markers and renal function were normal. Her Chest X-ray did not show any abnormalities. Cortisol and Thyroid function tests were also satisfactory. Abdominal CT scan showed dilated bowel loops suggestive of ileus. She was started on intravenous fluids (0.9% saline) and her sodium dropped to 115 mmol/l. His serum osmolality was 251 mmol/kg, urine osmolality 383 mmol/kg and urinary sodium was 78 mmol/l. He required an infusion of 1.8% Hypertonic saline on the intensive care unit. Her sodium incremented to 121 mmol/l in 24 hours.

Results and treatment: Although patient’s clinical history suggested dehydration, her serum and urine biochemistry revealed a degree of fluid overload with SIADH. This prompted the team to investigate for porphyria given the abdominal symptoms. Fluid restriction was commenced along with a urinary porphyria screen. Her sodium improved transiently with fluid restriction, but dropped again in the next few days to 115 mmol/l. She started having more back pains then. By that time, her urinary porphobilinogen/creatinine ratio result came back elevated at 93.1 μmol/mmol (NR 0-15), confirming the diagnosis of Acute Intermittent Porphyria. She was treated with IV Haeme arginate (Hemin) for 4 consecutive days and glucose loading. This improved her serum sodium gradually.

Conclusions and points for discussion: Hyponatraemia is common in acute intermittent porphyria, due to SIADH or gastrointestinal/renal sodium loss. The diagnosis of AIP is challenging due to non-specific symptoms, a wide list of differentials and unfamiliarity of many clinicians with appropriate testing and interpretation of results. Our case highlights the importance of keeping a high index of suspicion for acute porphyrias, in the evaluation of young patients with unexplained hyponatraemia and abdominal pain. Early diagnosis and treatment of symptomatic AIP can prevent long-term and life-threatening complications. Avoiding exacerbating factors (medications, diet and hormonal changes) plays an important role in preventing future attacks, and also in treating acute attacks. Advice from specialist porphyria services is available to clinicians 24/7.

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