Abdominal pain is a concerning clinical sign in peritoneal dialysis (PD) and often raises suspicion for peritonitis as the primary diagnosis. Peritonitis, typically presenting with abdominal symptoms and cloudy dialysis effluent [1], is the most common infectious complication in PD patients. It generally responds well to antibiotic therapy without requiring surgery. However, other abdominal conditions can mimic or coexist with peritonitis and should be considered, especially when peritonitis is refractory to antibiotics. These include surgical peritonitis due to organ perforation, pancreatitis, cholecystitis, and acute appendicitis [2]. Abdominal computed tomography (CT) and laparoscopy are particularly useful in the diagnosis and the management of such cases [3].

In this context, we report a rare case of a PD patient who developed acute appendicitis associated with peritonitis.

We present the case of a 39-year-old male with end-stage renal disease of unknown origin who had been undergoing CAPD since 2021.

Four months after initiating dialysis, he developed his first episode of peritonitis due to methicillin-sensitive Staphylococcus aureus, which was successfully treated with intraperitoneal (IP) cefazolin for 21 days based on the results of antibiotic susceptibility testing. The treatment resulted in full recovery without recurrence.

Two years later, the patient presented with abdominal pain and cloudy dialysis effluent, without fibrin or drainage abnormalities.

Clinical examination revealed a blood pressure of 160/100 mmHg and tachycardia at 118 beats per minute. There were no signs of fluid overload, and the patient was afebrile.

Peritonitis in PD patients is a common complication but is generally well treated with IP antibiotics. However, in this context, acute appendicitis represents a significant diagnostic challenge due to the attenuation of clinical symptoms specific to peritonitis. PD patients often present with atypical symptoms in cases of acute appendicitis due to the effect of peritoneal lavage: Frequent dialysate exchanges reduce bacterial load and delay abscess formation, thus masking typical signs such as localized pain or rebound tenderness[4][5]. Additionally, the use of IP antibiotics alters the inflammatory response and delays the diagnosis [5][6]. Persistent abdominal pain despite 48 hours of appropriate antibiotic treatment may indicate a secondary cause, such as appendicitis [1][2], while polymicrobial peritonitis involving enteric or anaerobic organisms serves as another warning sign [8]. In these cases, complementary exams play a crucial role: Abdominal CT, although often inconclusive, is essential for revealing the possibility of appendicitis or for ruling out other causes [9], while laparoscopy, recommended in cases of doubt, allows direct visualization and surgical management [10].

Appendicitis in PD patients can lead to peritoneal adhesions and catheter obstruction, as observed in our patient and supported by other cases in the literature where pelvic organs or inflamed appendices trap the catheter [9,11]. Delaying laparoscopy in these situations may increase morbidity and mortality [7][12]. Early surgical intervention, via laparoscopy or laparotomy, is essential to treat the appendicitis and reposition or replace the catheter if necessary. Resumption of PD at low volume is often possible after the procedure, although conversion to hemodialysis may sometimes be required[12][13].

Similarly, cases of acute appendicitis in PD patients presenting atypically are found in the literature. One case contains a description of catheter dysfunction caused by its insertion into adhesions in the lower right quadrant. The inflamed appendix, covered with fibrinopurulent exudate, was trapped against the catheter, which had to be repositioned in the pelvis after a successful appendectomy [2]. Another case involved a 23-year-old diabetic patient on PD who presented with Escherichia Coli BLSE peritonitis and who, 10 days after discontinuing the antibiotics, developed abdominal pain and turbid dialysate. The CT scan revealed perforated acute appendicitis with multiple abscesses and signs of intestinal obstruction, requiring appendectomy, adhesiolysis, and catheter removal. Despite these interventions, the patient died a few hours after surgery, highlighting the severity of these situations when not promptly managed [5].

In conclusion, acute appendicitis in patients on peritoneal dialysis poses a significant diagnostic challenge due to the symptom-masking effects of frequent dialysate exchanges and intraperitoneal antibiotics. Heightened vigilance is essential in the presence of persistent abdominal pain or catheter dysfunction, even in the absence of classical signs of peritonitis.

Radiological investigations, especially CT scanning, and early surgical intervention, via laparoscopy or laparotomy, perform an essential role in confirming the diagnosis and minimizing complications. These cases highlight the importance of rapid, multidisciplinary management to improve prognosis, although mortality remains high in complicated forms.