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USMLE® Step 1 Question of the Day: Abdominal Pain

Osmosis Team
Published on Feb 17, 2021. Updated on Feb 16, 2021.

Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics and help you prepare for the boards. Today's case involves an 8-year-old girl who's experiencing abdominal pain, fever, nausea, and vomiting. Can you figure out the cause?

An 8-year-old girl is brought to the emergency department by her parents due to worsening abdominal pain, fever, nausea, and vomiting for the last two days. Her parents report she has also had mild non-bloody diarrhea and the pain does not improve with defecation. When asked to localize the pain, the patient points to the right lower quadrant of her abdomen. She rates the pain as a 9 on a 10-point scale. Her medical history is non-contributory. Her temperature is 38.7 °C (101.7 °F), pulse is 86/min, respirations are 24/min, and blood pressure is 102/64 mmHg. On examination, palpation of the left lower quadrant of the abdomen elicits pain in the right lower quadrant. Laboratory tests are obtained and reveal a leukocyte count of 16,000/mm3. Which of the following is most likely associated with this patient’s condition? 

A. Noncaseating granulomas

B. Ectopic gastric tissue 

C. Lymphoid hyperplasia 

D. Gram-negative bacterial infection

E. “Target sign” on ultrasound

Scroll down to find the answer!


The correct answer to today's USMLE® Step 1 Question is...

C. Lymphoid hyperplasia

Before we get to the Main Explanation, let's look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

The incorrect answers to today's USMLE® Step 1 Question are...

A. Noncaseating granulomas

Incorrect: Noncaseating granulomas can be seen in the affected bowel segments of patients with Crohn's disease. Crohn's disease typically presents with chronic fatigue, crampy abdominal pain, bloody diarrhea, and low-grade fever. Moreover, non-caseating granulomas are also classically seen in sarcoidosis. However, this condition rarely causes gastrointestinal symptoms.

B. Ectopic gastric tissue

Incorrect: Ectopic gastric tissue is associated with Meckel's diverticulum, a congenital gastrointestinal anomaly which results from failure of involution of the omphalomesenteric (vitelline) duct. Patients with Meckel's diverticulum would present with abdominal pain and hematochezia. In this case, however, appendicitis is a much more likely diagnosis.

D. Gram-negative bacterial infection 

Incorrect: Yersinia enterocolitica, a gram-negative bacteria, can cause mesenteric lymphadenitis, which is also known as pseudoappendicitis due its similar presentation. Moreover, patients may experience bloody diarrhea. The pathogen is transmitted via undercooked foods, contaminated water, and contact with infected animals and their feces. In contrast, this patient has nonbloody diarrhea and no history of risk factors that may expose her to the pathogen.

E. “Target sign” on ultrasound

Incorrect: A “target sign” on ultrasound is associated with intussusception, which is defined as telescoping of one segment of the bowel into an adjacent segment. Patients with intussusception would present with colicky abdominal pain and currant jelly stools. Moreover, a sausage-shaped mass may be palpable on physical examination. 

Main Explanation 

This 8-year-old girl presents with greater than 24 hours of fever, nausea, vomiting, positive Rovsing sign (right lower quadrant pain that is elicited with palpation of the left lower quadrant), and worsening right lower quadrant abdominal pain. She most likely has appendicitis.

Appendicitis is caused by an initial obstruction of the appendix, which leads to buildup of intestinal fluid, mucous, and gut flora (primarily Escherichia coli and Bacillus fragilis) in the obstructed appendix. In children, the most common cause of appendiceal obstruction is lymphoid hyperplasia. In adults, the most common cause of obstruction is fecalith impaction. Other rarer causes include carcinoid tumor of the appendix, pinworm, eosinophilic appendicitis, and actinomycosis. 

As a result of the obstruction and subsequent buildup, the appendix grows in size and compresses the nearby afferent visceral nerves, which are carried to the T10 segment of the spinal cord, resulting in the initial periumbilical pain. The inflammation can then spread to the serosa of the appendix and the parietal peritoneum of the abdomen. Irritation of the parietal peritoneum, which is innervated by somatic nerves that also supply the overlying skin, results in migration of the pain to the right lower quadrant of the abdomen. 

The spread of this inflammation ultimately leads to weakening of the appendix wall, which can lead to appendiceal rupture. Bacteria can then escape into the peritoneum, leading to peritonitis and abscess formation. 


Major Takeaway 

Appendicitis is defined as inflammation of the appendix. In children, it typically results from lymphoid hyperplasia that obstructs the appendix. In adults, the obstruction is often the result of a fecalith. Patients present with acute-onset fever, nausea, vomiting, and right lower quadrant abdominal pain.

References

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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB.