A 17-year-old, previously healthy boy is brought to the emergency department due to a 3-day history of abdominal pain and diarrhea. The patient initially developed watery, loose stools with periumbilical pain that has since moved to the right lower quadrant. Over the past 24 hours, he has had 12 mucus-containing, loose bowel movements as well as nausea and fever. His younger brother has also had diarrhea, which has contained some streaks of blood, for the past few days but is now improving. Temperature is 38.8 C (101.8 F), blood pressure is 110/70 mm Hg, and pulse is 110/min. Examination shows mild diaphoresis. Right lower quadrant tenderness is present; there is no rebound or rigidity. Laboratory analysis shows a white blood cell count of 13,700/mm³ with 80% neutrophils. What is the most likely diagnosis?

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11ec25c8_d5e3_b675_bc81_596d905a4cad_MD0003_00 This patient has acute-onset fever, right lower quadrant (RLQ) pain, and leukocytosis with a neutrophilic predominance. These findings, in addition to vomiting and mild diarrhea, are often seen in acute appendicitis; however, appendicitis is not classically associated with profuse watery and now mucoid diarrhea and would not explain the presence of another sick contact with gastrointestinal symptoms (Choice A). The most likely cause of this presentation is infectious ileocecitis, which is often called pseudoappendicitis. Infectious ileocecitis is caused by organisms that have a predilection for infecting the ileocecal region, specifically Yersinia enterocolitica and Campylobacter jejuni. Most patients develop RLQ pain, although migratory abdominal pain, as seen in this patient, can occur in the setting of Campylobacter jejuni because it may initially infect the jejunum before spreading to the ileum and cecum. In addition to watery, mucoid, or bloody stools, other symptoms include fever, nausea, and vomiting. Imaging studies (eg, ultrasound, CT scan) may demonstrate ileocecal inflammation and mesenteric lymphadenopathy with sparing of the appendix. Stool studies (eg, multiplex PCR, culture) are diagnostic. Infectious ileocecitis often self-resolves but may require antibiotics in severe cases. In contrast to acute appendicitis, surgery is not typically required in infectious ileocecitis. (Choice C) Cecal diverticulitis causes RLQ pain, fever, and leukocytosis. Although mild diarrhea can occur, profuse or mucoid diarrhea is not seen. In addition, diverticulitis is exceedingly rare in children, making infectious ileocecitis far more likely in this 17-year-old patient. (Choice D) Although Escherichia coli O157:H7 causes abdominal pain and watery diarrhea, most patients develop hematochezia within 1-3 days of symptom onset. Moreover, fever >38.5 C (101.3 F) rarely occurs with this infection. (Choice E) Norovirus is a common cause of viral gastroenteritis and presents with watery diarrhea; stools with mucus are not seen. In addition, the white blood cell count is usually normal, and vomiting is a prominent symptom not seen in this patient. Educational objective: Infectious ileocecitis (ie, pseudoappendicitis) and acute appendicitis can present similarly with right lower quadrant pain, fever, and leukocytosis. However, the presence of profuse watery/mucoid diarrhea is highly suggestive of infectious ileocecitis; the most common causes are Yersinia enterocolitica and Campylobacter jejuni. References: Campylobacter infections in children. (http://www.ncbi.nlm.nih.gov/pubmed/30385582) Campylobacter. (http://www.ncbi.nlm.nih.gov/pubmed/30725718)

A 17-Year-Old, Previously Healthy Boy Is Brought to the Emergency