MON-067 A Perplexing Case of Hyponatremia and Abdominal Pain

Abstract

Previously healthy 20-year-old female presented with diffuse lower abdominal pain, cramping in nature, multiple episodes of emesis as well as urinary frequency. On day 2 of symptoms, she was treated for a urinary tract infection with antibiotics, as well as NSAIDs and opiates for pain relief. Her serum sodium was 133 mmol/L at this time. On day 3 of symptoms, a CT scan of the abdomen was performed however did not reveal pathology. Her serum sodium was 129 mmol/L at this time. She presented to our ED, on day 5 of symptoms, where serum sodium was down to 122 mmol/L. Despite IV fluids, her sodium continued to decrease to a nadir of 117 mmol/L. Further testing, including a serum osmolality of 242 mOsm/kg, urine osmolality of 540 mOsm/kg, and urine sodium of 207 mmol/L, was consistent with a diagnosis of SIADH. Given persistence of abdominal symptoms along with SIADH further imaging studies, including US abdomen, CT brain and Chest XR, were ordered and returned unremarkable. The constellation of SIADH along with persistent abdominal pain, with negative imaging, lead to consideration of acute intermittent porphyria as a diagnosis. Random urine porphobilinogen was found to be elevated to 147.2 mcmol/L (≤ 2.4) leading to the presumptive diagnosis of acute intermittent porphyria presenting as a neurovisceral attack. Biochemical and genetic testing is being pursued to confirm her diagnosis.Acute intermittent porphyria is an autosomal dominant hematologic disorder characterized by deficiency in porphobilinogen deaminase, an enzyme in the heme synthesis cascade. Acute attacks are caused by accumulation of porphyrin resulting in autonomic and peripheral neuropathy which can present as abdominal pain, urinary retention, polyneuropathy, dark urine and psychiatric disturbance. Hyponatremia is present in 25–60% of cases which is caused by SIADH or sometimes renal and gastrointestinal sodium loss. Triggers for acute attacks include medications, starvation, infections, hormonal changes and alcohol. Treatment includes avoidance of triggers, IV dextrose and high carbohydrate diet. In severe attacks, IV hemin is used.Our patient’s urinary tract infection likely triggered her acute symptoms, which was further exacerbated by treatment with NSAIDS and opiates. She developed SIADH which improved with hypertonic saline and fluid restriction.This case illustrates the need to consider acute intermittent porphyria in the differential diagnosis of SIADH presenting with abdominal pain of unknown etiology.