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Recurrent Exit-Site Infection Due to Staphylococcus lugdunensis—A Virulent Coagulase-Negative Staphylococcus

(While on CAPD, her calcium and phosphorus levels were normal, except once, 2 years before presentation, when serum calcium was 2.9 mmol/L; Ca×P never exceeded 5 mmol2/L2). She performed CAPD 4 times daily using 2 L of 1.5% glucose solution until 2 months before admission, when her regimen was reduced to 3 times daily (also with 2 L of 1.5% glucose solution). The solution contained 1.75 mmol/L calcium and 0.5 mmol/L magnesium. The stone in the case described by Antoniou et al. (1) and the stone in our patient were similar: each had a soft core with a crust, and both were brown, oval, and made of calcium and phosphorus. Antoniou et al. suggested that the catheter intraluminal stone in their patient could be a result of calcium and phosphorus disorder attributable to uncontrolled secondary hyperparathyroidism (1). However, our patient had normal parathyroid hormone levels and no peritonitis or exit-site infection from the very start of dialysis. So what is the underlying cause of the intraluminal stone here? Of the cases of peritoneal calcification described in patients on CAPD, most have been attributed to a high incidence of peritonitis, peritoneal sclerosis, uncontrolled secondary hyperparathyroidism, and long-term PD (2–5). None of those factors was present in our patient. It should be noted that, 5 months before the event reported here, our patient participated in a study in which we measured intraperitoneal concentrations of interleukin 6 (IL-6). Her effluent level of IL-6 (9.6 pg/mL) was above the group average (7.87 pg/mL); IL-6 is a strong marker of local peritoneal inflammation. In conclusion, it seems that chronic intraperitoneal inflammation or less-frequent PD fluid exchanges may contribute to the formation of stones in the peritoneal catheter. However, formation of stones in the peritoneal catheter is a very rare complication of PD. If the stone is larger (as in the case described by Antoniou et al., 3.9×3.0 mm), it can cause failure and removal of the catheter. In this case, the stone was small and could be extracted (the Tenckhoff catheter radius is 2.6 ± 0.1 mm), maintaining normal catheter function.