Endocrine Abstracts

Background: Acute intermittent porphyria (AIP) is an inherited autosomal dominant disorder characterized by hepatic deficiency of hydroxymethylbilane synthase (HMBS)/porphobilinogen deaminase (PBGD), the third enzyme of the heme synthesis pathway. Hyponatremia is one of the main presenting symptoms and it is thought to be related to an inadequate secretion of ADH (SIADH). Since AIP is an uncommon disease, there is little information about how AIP related hyponatremia responds to standard treatment.

Case presentation: We report the case of a 51−year−old woman who got admitted to the emergency room for acute abdominal pain and dizziness. Physical examination and laboratory tests showed a severe euvolemic hyponatremia with serum sodium (SNa) 119 mEq/l, urine osmolarity 933 mOsm/l and urine Na 149 mEq/l, all of them compatible with SIADH. A sodium chloride 3% infusion at 0.5 ml/kg/h was started. SNa rose to 121 mEq/l after 24 h. In the following days SNa stabilized at 121–122 mEq/l despite water intake restriction, and tolvaptan was started. Following our standard treatment protocol for SIADH related hiponatremia, we started with a tolvaptan dose of 7.5 mg. SNa increased to 122 mEq/l at 24 h and tolvaptan was increased to 15 mg/day on the second day. Without further dose increment, SNa progressively reached normal values within five days. As the patient complained of abdominal pain, AIP was suspected and a Hoesch test confirmed the diagnosis. Treatment with hemin was started, which improved the patient ’s clinical signs and normalized the δ-aminolaevulinic acid (ALA) and porphobilinogen (PBG). SNa further increased to 142 mEq/l and tolvaptan was progressively decreased and finally discontinued, with SNa manteined in normal range thereafter.

Discussion and conclusion: As treatment of acute porphyria attacks is mainly based on intravenous administration of glucose 10% and/or human hemin, previous correction of hyponatremia is of paramount importance to avoid further decrease of SNa caused by large amounts of glucose solutions. In our case, the time frame for response to tolvaptan and the dose needed to achieve eunatremia were similar to those for SIADH-associated hyponatremia from a different origin. Thus, tolvaptan is an effective option to guarantee a desired serum sodium increase during acute porphyria attack to safely permit handling high volumes of glucose solutions. Standard protocols for treatment of SIADH related hyponatremia with tolvaptan can be applied to AIP; however, the treatment will only be maintained for the duration of the acute condition.