Sodium polystyrene sulfonate-associated colonic perforation

Electrolyte Disordersmedium

A 57-year-old man with CKD stage 3b, and GERD is admitted for elective right knee arthroplasty. He has had several days of constipation. Surgery is uncomplicated (minimum BP 92/68 mm Hg). Postoperative potassium is 6.1 mEq/L, treated with insulin, dextrose, and two doses of sodium polystyrene sulfonate. Hospital medications include cefazolin, insulin, famotidine, oxycodone, and prophylactic heparin. On day 3 he develops severe lower abdominal pain, decreased bowel sounds, and BP 95/40 mm Hg. Hemoglobin falls from 9.2 to 7.5 g/dL; lactate is normal. Abdominal x-ray shows free air under the diaphragm. What is the most likely diagnosis?

  1. A.Perforated duodenal ulcer
  2. B.Mesenteric ischemia
  3. C.Perforated colonCorrect
  4. D.Clostridium difficile colitis

Explanation

The most likely diagnosis is a perforated colon from sodium polystyrene sulfonate (SPS)-associated colonic necrosis. He received two doses of SPS for postoperative hyperkalemia in the setting of several days of preexisting constipation, postoperative opioid therapy (oxycodone), and reduced bowel motility after surgery. Two days later he developed severe lower abdominal pain, ileus, hypotension, a fall in hemoglobin, and free intraperitoneal air. SPS crystals can adhere to and injure the colonic mucosa, causing transmural necrosis, ulceration, bleeding, and perforation, most often in the cecum, right colon, or sigmoid. Risk factors include the postoperative state, constipation or ileus, opioids, uremia, hypovolemia, and administration with sorbitol. Histology shows basophilic, rhomboid crystals with a fish-scale pattern in necrotic mucosa. Mortality is high, and treatment is urgent surgical resection. These risks, combined with SPS's slow, unpredictable effect, are why newer binders (patiromer or sodium zirconium cyclosilicate) are preferred, and why SPS should be avoided in postoperative patients and those with bowel dysmotility. Mesenteric ischemia can cause severe pain, ileus, and perforation, but it typically occurs with atrial fibrillation, low-flow states, or vascular disease and is accompanied by elevated lactate. His lactate is normal, and there is a clearer drug-related cause. Clostridioides difficile colitis may follow cefazolin exposure, but it presents with diarrhea, leukocytosis, and fever. Perforation occurs only with fulminant colitis or toxic megacolon, and he is constipated. A perforated duodenal ulcer causes sudden epigastric pain with free air, but he is taking famotidine, the pain is in the lower abdomen, and the temporal association with SPS points to the colon.

Why each option

A.
A perforated duodenal ulcer causes sudden epigastric pain, whereas his pain is lower abdominal, he takes famotidine, and onset followed SPS.
B.
Mesenteric ischemia usually occurs with low-flow states or atrial fibrillation and raises serum lactate, which is normal here.
C.
Correct. Lower abdominal pain, ileus, hemoglobin drop, and free air after SPS in a constipated postoperative patient on opioids indicate SPS-induced colonic perforation.
D.
C. difficile colitis presents with diarrhea, fever, and leukocytosis; perforation requires fulminant colitis, and he is constipated.

Reference: Harel Z, Am J Med 2013 (gastrointestinal adverse events with sodium polystyrene sulfonate: a systematic review)

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