The patient who presents with lethargy poses a diagnostic challenge. The many life-threatening conditions that can cause lethargy in a child must be considered based on signs, symptoms, time course of the disease, and the patient’s age.
The mnemonic for altered level of consciousness in children is AEIOUTIPS:
Insulin/Intussusception/Inborn errors of metabolism
Given the symptoms of abdominal pain, vomiting, and diarrhea, intussusception and dehydration are high on the differential.
If the cause of lethargy had been dehydration, the patient’s mental status would have improved after 40 mL/kg of normal saline. Because it did not, intussusception is more of a concern.
If the patient had had vomiting and lethargy without diarrhea, other items on the differential would be more concerning. If the patient had not had diarrhea, an intracranial mass, meningitis, encephalitis, and possibly toxic ingestion would be higher on the differential.