AIP found to be cause of woman’s abdominal pain, SiADH: Case study

Confounding symptoms can often hamper and delay diagnosis of AIP

Joana Vindeirinho, PhD avatar

by Joana Vindeirinho, PhD |

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A woman with unexplained abdominal pain and syndrome of inappropriate antidiuretic hormone secretion (SiADH) was eventually diagnosed with acute intermittent porphyria (AIP) after initial testing and misdiagnoses, a new case study reports.

In SiADH, overproduction of antidiuretic hormone (ADH) causes the kidneys to reduce filtration significantly and retain more water, creating an imbalance of fluid and salts in the body. Although SiADH can be a feature of an AIP attack, the rarity of the disease and the lack of diagnosis made it harder for doctors to connect the woman’s SiADH to an AIP attack.

“This case highlights AIP as a rare but important cause of abdominal pain and as a cause for unexplained SiADH,” the researchers wrote.

The case study, “Acute intermittent porphyria: A rare cause of syndrome of inappropriate antidiuretic hormone secretion,” was published in the Journal of the Royal College of Physicians of Edinburgh.

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AIP often overlooked as potential cause of patient’s symptoms

AIP is a type of acute porphyria, caused by mutations in the HMBS gene. These mutations affect the production of heme, a key molecule that is required for oxygen transport in cells, causing a buildup of heme precursors, such as porphyrias, in tissues that can become toxic.

A timely diagnosis is important to prevent AIP-related complications but, because its symptoms are often nonspecific, AIP is frequently overlooked as a potential cause of a patient’s condition.

In this report, researchers described the case of a 31-year-old woman who visited an emergency department in the U.K. complaining of abdominal pain, constipation, and vomiting that had been going on for 10 days. She also had pain in her lower back and thighs.

Her medical history was unremarkable, save for some kidney and urinary tract infections, for which she had recently been treated with antibiotics. She also reported dieting to lose weight in the preceding month, and she had taken laxatives to help with weight loss, but had not done so recently.

On first examination, the woman did not have any signs of excess fluid buildup or dehydration. However, doctors considered her to be dehydrated because of her vomiting and recent reduced intake. She had high blood pressure and slightly high blood sugar levels. Sodium levels were very low in her blood, but very high in her urine.

This case highlights AIP as a rare but important cause of abdominal pain and as a cause for unexplained SiADH [syndrome of inappropriate antidiuretic hormone secretion].

Woman had CT scans, laboratory tests, and treatment for hypovolemic

The woman underwent several CT scans to rule out a possible malignancy, with normal results. She was initially treated for hypovolemia, a condition that occurs when the body does not have enough fluids, and received replacement fluids administered into the vein (intravenously). However, this caused her blood sodium levels to continue dropping for the next two days.

Her doctors changed tactics and restricted her fluid intake for the following three days. At this point, they determined that she was not hypovolemic, but had normal fluid volume accompanied by low blood sodium levels and very high urine sodium levels. This led them to suspect SiADH, which was confirmed by laboratory test results.

Fluid restriction was tightly controlled, and the woman received salt tablets to help restore sodium levels. However, her sodium levels dropped even further the following day. She started receiving an intravenous solution rich in sodium and treatment with the antibiotic demeclocycline, which can be used to help treat SiADH.

Her blood sodium levels continued to decline, and she started hallucinating as a result. To improve treatment with the sodium-rich solution, doctors started administering it through a catheter inserted into a central vein (usually one in the neck, inner thigh, or under the arm).

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Urine test results point to AIP diagnosis

After 48 hours, her sodium levels rose, and her neurological symptoms eased. Once her sodium levels stabilized and her condition continued to improve, the woman was discharged from the hospital, but with scheduled monitoring to ensure her safety.

Urine tests done during her hospital stay showed that she had very high values of both porphyrin/creatinine ratio and porphobilinogen/creatinine ratio, indicating a buildup of porphyrins and their precursors. These elevated values, along with her other symptoms, pointed to a diagnosis of AIP, which was later confirmed.

AIP is known to cause SiADH by stimulating the production of ADH and water retention in the intestines. However, because of its rarity, AIP can be overlooked as a possible cause. In this case, the woman had no previous AIP diagnosis, and this was her first AIP attack. For every AIP attack, it is important to understand what might have triggered it.

“Interestingly in this case the patient had recently been prescribed pivmecillinam [an antibiotic] and had described recent attempts to lose weight, both of which could have been relevant triggers,” the researchers wrote.