Fast Five Quiz: How Much Do You Know About Appendicitis?

Jaime Shalkow, MD


December 09, 2016

The classic history of anorexia and periumbilical pain followed by nausea, RLQ pain, and vomiting occurs in only 50% of cases. Nausea is present in 61%-92% of patients; anorexia is present in 74%-78% of patients. Neither finding differs statistically from findings in patients who present to the emergency department with other etiologies of abdominal pain.

In addition, when vomiting occurs, it nearly always follows the onset of pain. Vomiting that precedes pain is suggestive of intestinal obstruction, and the diagnosis of appendicitis should be reconsidered. Diarrhea or constipation is noted in as many as 18% of patients and should not be used to rule out appendicitis.

The most common symptom of appendicitis is abdominal pain. Typically, symptoms begin as periumbilical or epigastric pain migrating to the RLQ of the abdomen. This pain migration is the most discriminating feature of the patient's history, with a sensitivity and specificity of approximately 80%, a positive likelihood ratio of 3.18, and a negative likelihood ratio of 0.5.

The pain migration is explained by the fact that the visceral peritoneum is innervated by thin, low-myelin nerve fibers, which conduct stimuli slowly (0.3 m/sec), thus rendering the brain incapable of accurately localizing the pain. When the appendix is inflamed, the brain is able to know only that such stimuli come from somewhere in the midgut, and the pain is felt around the umbilicus. As disease progresses and the full thickness of the appendix gets inflamed, the parietal peritoneum is affected. The latter is innervated by thick, myelin-rich fibers, which conduct stimuli very fast (120 m/sec). Thus, the brain is able to specifically pinpoint the anatomical origin of the pain in the RLQ.

Patients usually lie down, flex their hips, and draw their knees up to reduce movement and to avoid worsening their pain. Later, the patient describes a worsening progressive pain, along with vomiting, nausea, and anorexia. Usually, fever is not present at this stage.

For more on the presentation of appendicitis, read here.


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