Pseudoappendicitis can describe any condition mimicking appendicitis. Acute right lower quadrant abdominal pain with anorexia and point tenderness (McBurney's sign) are characteristic symptoms of appendicitis. The more specific definition of pseudoappendicitis is associated with Yersinia enterocolitica infections. This bacteria is associated with the infective and inflammatory intestinal condition known as yersiniosis. Most cases of Y. enterocolitica, however, are asymptomatic and self-limiting.
Yersinia is a gram-negative bacillus of the Enterobacteriaceae family. There are 11 subtypes of Yersinia with only 3 that are pathologic to humans. Yersinia pestis, Yersinia pseudotuberculosis, and Y. enterocolitica can all cause diseases in man. Y. enterocolitica can be found in all species of animals including mammals such as dogs, pigs, cattle, deer and rodents, many types of birds, and even reptiles. It is harbored in their intestinal tract until passed along to humans. This bacteria can also be isolated in ponds and the soil. It is usually passed on to humans by direct contact with a contaminated material such as contaminated water or milk. Eating undercooked pork is a very common route of human infection.
Immunocompromised patients are more susceptible to infections from Y. enterocolitica. They are also prone to developing more severe sequelae of the disease. Sequelae include sepsis and splenic and hepatic abscesses from dissemination of the bacteria from the gut to these organs and the bloodstream. Individuals with hereditary hemochromatosis are more prone to acquiring Y. enterocolitica infections. This condition is associated with higher than normal total iron levels in the blood. Y. enterocolitica is a siderophilic (iron-loving) bacteria, in fact, Y. enterocolitica is the most commonly found bacteria in contaminated units of stored packed red blood cells. Most otherwise healthy patients who contract these bacteria exhibit self-limiting gastrointestinal symptoms, but the very young, elderly or very sick are more likely to acquire this infection and are more likely to develop symptoms. People who exhibit poor personal hygiene may also be at an increased risk of infection. Patients who have recently received a blood transfusion who develop symptoms not characteristic for transfusion reactions such as generalized malaise, gastrointestinal (GI) symptoms, fever, and abdominal pain should be worked up for Y. enterocolitica bacteremia. This is because of the correlation between infected stored blood products and Y. enterocolitica. 
Y. enterocolitica is mainly a disease of the GI tract. It results from direct contact and ingestion of contaminated material, water, and food. It is carried and harbored by virtually all species of animals, water, and soil. After it is ingested, it resides and replicates in the terminal ileum of humans. It then progresses to mesenteric lymph nodes causing mesenteric lymphadenitis. Often this will mimic acute appendicitis, thus the term pseudoappendicitis. This disease is usually self-limiting in healthy individuals. The most common complaint being GI symptoms such as diarrhea, fever, and abdominal pain, but it can progress to more severe symptoms such as bloody diarrhea, dehydration, and severe abdominal pain. More advanced cases may develop sepsis, bacteremia, and abscesses of the liver and spleen. 
Y. enterocolitica can be isolated from infected tissues, blood, stool, water, and almost any contaminated materials. It causes varying degrees of enteritis with inflammation of the mucosa of the GI tract. Histologic findings similar to salmonella and Shigella infections are usually present. Mesenteric lymph nodes will show signs of inflammation and adenitis. Y. enterocolitica bacteria can also be cultured from these sources.
Y. enterocolitica is serotyped into around 60 serogroups by their O lipopolysaccharide surface antigens. Most subtypes are nonpathologic to humans. Serogroups that are harmful to humans are O:3 and O:9, which are most common in Europe, and serogroup O:8 which is most prominent in the United States. Animals and humans who are infected with this bacteria and who never develop symptoms or convalesce from a symptomatic episode may become carriers and will harbor the Y. enterocolitica bacteria in their GI tract. 
Most patients who contract Y. enterocolitica never develop symptoms. Often mild symptoms of diarrhea and abdominal pain may occur during yersiniosis. More advanced signs of this infection include watery or bloody diarrhea, fever, chills, and increased abdominal pain. If mesenteric adenitis is also present patients will have moderate to severe right lower quadrant abdominal pain. This is easily mistaken for acute appendicitis. They may exhibit abdominal guarding and rebound tenderness with McBurney's sign (point tenderness one-third of the way between the umbilicus and the anterior superior iliac crest). Localized adenitis causes this at the terminal ileum where most of the bacteria are concentrated. Extreme watery or bloody diarrhea is often misdiagnosed as salmonellosis, shigellosis, or Giardia enteritis. Patients with advanced infections especially those left untreated will present with signs of sepsis, dehydration, and shock. 
Lab and radiologic tests are done more for excluding other etiologies such as appendicitis, Meckel's diverticulitis, or inflammatory bowel diseases. Stool cultures should be done to make the diagnosis of Y. enterocolitica. If this particular bacteria is suspected, the microbiology department should be notified because isolation of this organism from stool requires the use of a special Cefsulodin-Irgasan-Novobiocin (CIN) agar. In severe progressive cases, especially in immunocompromised patients, CT imaging may be needed to confirm or rule out intrahepatic or splenic abscesses. 
Most Y. enterocolitica infections are self-limiting and require no treatment. Patients with more pronounced symptoms of diarrhea and dehydration should first be treated symptomatically. They will need to be resuscitated with intervenous fluids and stabilized. Appropriated lab tests and x-rays should be ordered to rule out other possible surgical etiologies of their symptoms. As this is often a self-limiting condition, antibiotics are usually not required, but in more advanced cases, cases that do not respond to symptomatic therapy or cases of immunocompromised patients, antibiotics should be initiated. Because this is a beta-lactamase producing bacteria, penicillins, and first and second generation cephalosporins are ineffective and should not be used. The recommended antibiotic therapy for Y. enterocolitica is a combination of doxycycline and an aminoglycoside. Other antibiotics that have been proven effective in treating this condition are trimethoprim-sulfamethoxazole, fluoroquinolones, chloramphenicol, and third-generation cephalosporins. Immunocompromised patients with splenic or hepatic abscesses may respond to percutaneous drainage of these abscesses. Long-term intervenous antibiotics should also be administered. 
Appendicitis is probably the most well-known misdiagnosis of patients with Y. enterocolitica infections thus the term pseudoappendicitis. Other differential diagnoses to rule out would be inflammatory bowel disease, Meckel's diverticulitis, mesenteric lymphadenitis, ischemic colitis and sigmoid diverticulitis. There are many infective causes of similar symptoms that must be ruled out. These include various parasitic infections, Giardiasis, salmonellosis, shigellosis, and Clostridium difficile colitis. 
This disease is most often self-limiting. Treating the symptoms with fluids, rest, and fever control is usually sufficient, and patients recover fully after 24 to 48 hours. Immunocompromised patients or patients with the more systemic disease will have a poorer prognosis. 
There are no identifiable long-term sequelae of this disease. Some studies speculated that patients with prolonged courses of this condition might develop autoimmune thyroid disease or other auto-immune pathology; however, this has not been proven. 
Often patients are misdiagnosed with appendicitis and undergo an appendectomy. The diagnosis of Y. enterocolitica is never made because their symptoms subside without treatment and they feel better just by receiving intravenous antibiotics during the perioperative period. This condition is undoubtedly underdiagnosed. 
Collecting an accurate history usually leads to the correct diagnosis of pseudoappendicitis. Knowledge of the epidemiology and treatment of this condition could spare the ill patient an unnecessary surgery. The clinician must also be patient, as the appropriate treatment of this condition is supportive care. Awareness of the self-limiting nature of this disease is mandatory for the treating staff and patient.
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