USMLE® Step 1 Question of the Day: Maternal infection

USMLE® Step 1 Question of the Day: Maternal infection

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This week, we are sharing another USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case focuses on a 28-month-old with unusual clinical features. Can you identify the most likely cause behind the disseminated rash, hepatosplenomegaly, and distinctive facial and skeletal abnormalities?Test your diagnostic skills with this USMLE Step 1 question.

A 28-month-old boy is brought to the pediatrician for a routine evaluation. The patient was born via vaginal delivery at 38-weeks of gestational age. The patient’s mother received minimal antenatal care. During the third trimester of pregnancy, the mother had developed a disseminated maculopapular rash involving the palms and soles and arthralgias. The patient’s weight is at the 25th percentile, and head circumference is at the 50th percentile. Vitals are within normal limits. Abdominal examination reveals hepatosplenomegaly. A depressed nasal bridge, notched incisors, and bowing of the tibia are also observed. Cardiovascular examination is unremarkable. Which of the following is the most likely cause of this patient’s condition? 

A. Spirochete bacteria

B. Obligate intracellular protozoan

C. Enveloped, double-stranded DNA virus

D. Enveloped, single-stranded RNA virus

E. Gram-positive cocci in chains

Scroll down for the correct answer!

The correct answer to today’s USMLE® Step 1 Question is…

A. Spirochete bacteria

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

B. Obligate intracellular protozoan

Incorrect: Congenital toxoplasmosis is caused by the protozoan Toxoplasma gondii. The condition can lead to chorioretinitis, hydrocephalus, microcephaly, and intracranial calcifications. In contrast, the facial features and bone abnormalities seen in this patient are not typically associated with congenital toxoplasmosis.

C.  Enveloped, double-stranded DNA virus 

Incorrect: Cytomegalovirus (CMV) is an enveloped, double-stranded DNA virus. Congenital CMV infection can lead to hepatosplenomegaly, microcephaly, periventricular calcifications, and hearing loss. The characteristic facial features in this patient are not present in individuals with congenital CMV infection.

D. Enveloped, single-stranded RNA virus 

Incorrect: Maternal infection with rubella can present with a self-limited maculopapular rash and arthralgias. However, congenital rubella is characterized by cataracts, sensorineural hearing loss, and congenital heart defects. The absence of these findings in this patient makes the diagnosis of congenital rubella syndrome unlikely.

E. Gram-positive cocci in chains

Incorrect: Neonates infected with group B streptococcus (GBS), which appears microscopically as chains of Gram-positive cocci, can present with sepsis, meningitis, and encephalitis. Fetuses can acquire GBS via exposure to vaginal bacteria during the childbirth process. However, GBS infection would not account for this patient’s facial and tibial deformities.

Main Explanation

This infant has a depressed nasal bridge, notching of the incisors, bowing of the tibia, and hepatosplenomegaly. These findings are consistent with the clinical manifestations of congenital syphilis. Furthermore, the mother has a history of a maculopapular rash and arthralgias, indicating a maternal infection with secondary syphilis. 

Syphilis is a sexually transmitted disease caused by the spirochete Treponema pallidum. During pregnancy, maternal syphilis infection produces symptoms similar to those in a non-pregnant adult. Symptoms may include a painless papule (primary syphilis), maculopapular rash, pharyngitis, mucocutaneous lesions (secondary syphilis), as well as cardiovascular and neurological involvement (tertiary syphilis).

Syphilis can be vertically transmitted via the placenta, resulting in congenital syphilis. Most neonates are asymptomatic at birth but can subsequently develop manifestations of congenital syphilis. Early symptoms (<2 years of age) include generalized lymphadenopathyfever, and a maculopapular rash affecting the palms and soles. Later symptoms of congenital syphilis include dental deformities (Hutchinson teeth), skeletal abnormalities (anterior bowing of the tibia), hepatosplenomegaly, saddle nose deformity, and sensorineural hearing loss. Fortunately, congenital syphilis can be prevented via early screening, identification of maternal infection, and treatment with penicillin.  

table of congenital torch infections

Major Takeaway

Congenital syphilis is caused by transplacental transmission of the spirochete Treponema pallidum. Clinical manifestations of congenital syphilis include rashskeletal and dental abnormalities, and sensorineural hearing loss. The condition can be prevented via early screening, maternal infection identification, and penicillin treatment. 

References

Rathbun, K.C. (1983) Congenital syphilis. Sexually Transmitted Diseases. 10(2), 102-107. Doi: 10.1097/00007435-198304000-00009.

Ricci, J.M., Fojaco, R.M., O’Sullivan, M.J. (1989) Congenital syphilis: The University of Miami/Jackson Memorial Medical Center experience, 1986-1988. Obstetrics and Gynecology. 74(5), 687-693. PMID: 2812644.

Woods, C.R. (2005) Syphilis in children: Congenital and acquired. Seminars in Pediatric Infectious Diseases. 16(4), 245-257. Doi: 10.1053/j.spid.2005.06.005. 

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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. 


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