Inflammatory Pseudotumor Containing Kayexalate Crystals: A Case Report and Review of the Literature

Abstract

Introduction: Kayexalate or sodium polystyrene sulfonate has long been used for the treatment of hyperkalemia. Inflammatory pseudotumor (IP) is a benign inflammatory mass, and occurs secondary to infection or foreign body. We present a case of an extra-intestinal IP containing Kayexalate crystals. Case Report: A 62-year-old woman with history of type II DM and CKD presented with abdominal pain. Surgical history included a partial colectomy with colostomy for diverticulosis. Her medication regiment included Kayexalate. She was febrile upon presentation, and had tenderness over the right side of the abdomen. A CT scan revealed a mass below the liver and near the ostomy(Fig 1A). She was started on antibiotics and underwent surgical evacuation of the mass, with cultures positive for E. coli. A repeat CT scan showed a residual mass in the same location, but smaller in size. Biopsy of the mass showed spindle and stellate cells mixed with histiocytes and inflammatory cells. Occasional polygonal crystals with a “fish scale” appearance were found (Fig 1B). The crystals were highlighted by PAS stains.Figure 1: A) CT Abdomen with mass in the RLQ. B) Polygonal crystals with “fish scale” appearance.Discussion: Kayexalate is used to treat hyperkalemia, promoting excretion of potassium ions into the intestine. It is often administered with sorbitol to prevent impaction. Sorbitol has been known to cause intestinal necrosis, resulting in mild GI bleeding to perforation. Sorbitol-induced intestinal necrosis is thought to be from increased prostaglandin activity and vasospasm. Identification of Kayexalate crystals is considered the hallmark of Kayexalate toxicity. These crystals have a polygonal and “fish scale” appearance that display a red color on PAS stains. IP is often considered to be a benign mass, and composed of spindled myofibroblasts set in dense collagen and inflammatory cells. Their etiology is thought to be a reactive process in response to infection or foreign body. Our patient developed ischemic colitis, which is found in previously-reported cases of GI complications to Kayexalate, and formed an abscess. Following evacuation, the abscess likely evolved into an IP. We hypothesize the IP is attributed to an infectious etiology, with the Kayexalate crystals coming to reside in the lesion, consistent with other case reports. Regardless, the presence of Kayexalate in this case is unique in its location and association with an IP.