First Aid for the USMLE Step 2 CS

Section 4. Practice Cases

Case 40. 6-Month-Old Girl with Diarrhea


Opening Scenario

The mother of Theresa Wheaton, a 6-month-old female child, calls the office complaining that her child has diarrhea.

Examinee Tasks

1. Take a focused history.

2. Explain your clinical impression and workup plan to the mother.

3. Write the patient note after leaving the room.

Checklist/SP Sheet

Patient Description

The patient’s mother offers the history.

Notes for the SP

Show concern about your child’s health, but add that you don’t want to come to the office unless you have to because you do not have transportation.

Challenging Questions to Ask

“How sick is my baby?”

Sample Examinee Response

“It is hard for me to give you an accurate answer over the phone. I would like you to bring your baby here so that I can examine her and perhaps run some tests. After that, I should be able to give you a more accurate assessment.”

Examinee Checklist

Building the Doctor-Patient Relationship Entrance

 Examinee introduced self by name.

 Examinee identified his/her role or position.

 Examinee correctly used patient’s name and identified caller and relationship of caller to patient.

Reflective Listening

 Examinee asked an open-ended question and actively listened to the response.

 Examinee asked the SP to list his/her concerns and listened to the response without interrupting.

 Examinee summarized the SP’s concerns, often using the SP’s own words.

Information Gathering

 Examinee elicited data efficiently and accurately.

 Examinee showed compassion for the SP and her child.

Connecting with the Patient

□ Examinee recognized the SP’s emotions and responded with PEARLS.

Physical Examination



 Examinee discussed initial diagnostic impressions.

 Examinee discussed initial management plans:

□ Follow-up tests.

 Examinee asked if the SP had any other questions or concerns.

Sample Closure

Ms. Wheaton, from the information you have given me, I am concerned that your child may be dehydrated. She hasn’t urinated since yesterday, and she is weak and drowsy. It is very hard for me to assess her over the telephone, and I do not want to jeopardize her health in any way. For this reason, I am going to ask you to bring her in for a physical exam and a full assessment, and we will then proceed according to what we find on the exam. I understand that you may have problems with transportation, but we are fortunate to have a social worker here who can help you handle these issues. After we are done on the phone, I will transfer your call to him, and he can help you. Do you have any questions for me?


HPI: The source of information is the patient's mother. The mother of a 6-month-old F c/o her child having 1 day of diarrhea, weakness, and drowsiness. The child has had 6 watery brown bowel movements per day. There was no blood in her stool, but she has not urinated since yesterday. She received Tylenol without improvement. The mother reports the child's temperature as 100.5°F and adds that her mouth is dry. The child has no known sick contacts but is in day care. The mother denies any vomiting, lethargy, excessive sleeping, abnormal behavior, or recent URIs. The child had a normal checkup with her pediatrician 2 weeks ago and is up to date on her immunizations. She has a diet of formula with iron and rice cereal at night with occasional juice.

ROS: Negative.

Allergies: NKDA.

Medications: None.

PMH: Uncomplicated spontaneous vaginal delivery.

PSH: None.

FH: Noncontributory.

Physical Examination


Differential Diagnosis


Patient Note Differential Diagnoses

 Viral gastroenteritis: This is the most common cause of pediatric acute infectious diarrhea. Rotavirus was the most likely cause until the introduction of rotavirus vaccine into the routine infant immunization schedule. Viral gastroenteritis cases are now caused by other viruses (primarily norovirus).

 Bacterial diarrhea: The most common types of bacterial diarrhea are Shigella, Salmonella, Campylobacter jejuni, Aeromonas, and Yersinia enterocolitica. E coli and Clostridium species are normal intestinal flora, but pathogenic strains are capable of causing bacterial diarrhea.

 Malabsorption: This condition may result from a baby’s consumption of juice and may be the culprit in the current patient’s case. It is important to counsel parents that juice should not be introduced into the diet of babies in this age group. Some children may have milk intolerance as well. However, milk intolerance would probably not present as acutely as is seen here.

Additional Differential Diagnoses

 UTI: Diarrhea in infants may be a nonspecific response to an infection such as UTI or pyelonephritis.

 Intussusception: Given the severe nature of this disease, intussusception must be considered in the differential. The classic presentation includes abdominal pain, vomiting, and bloody (“currant jelly”) stools. Some 75% of patients with intussusception have only two of these findings. Intussusception is also associated with recent viral illness and low-grade fever.

 Bacteremia: Bacteremia/sepsis should be ruled out in any child with high fever, drowsiness, and no urine output.

Diagnostic Workup

 Rotavirus enzyme immunoassay/norovirus PCR: Rotavirus can be detected through the rotavirus enzyme immunoassay. Norovirus, previously known as the Norwalk virus, can be detected through PCR amplification. Serum titers for norovirus can be positive within two weeks of initial symptoms.

 Electrolytes: Children with diarrhea frequently have metabolic acidosis or other electrolyte abnormalities, such as hyponatremia.

 Stool leukocytes, culture, ova and parasitology, and pH: WBCs in the stool would suggest an infectious etiology, and culture may reveal a bacterial pathogen. Microscopy may reveal ova or parasites such as Giardia, an infection that is common among day care attendees. Stool pH can distinguish a secretory from an osmotic cause of diarrhea by revealing a pH of > 6 or < 5, respectively.

 UA: To assess for pyelonephritis or UTI.

 AXR: A plain film abdominal radiograph should pick up characteristics of bowel obstruction in intussusception.

 Blood cultures: To rule out bacteremia.

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