A 24-year-old woman, gravida 1 para 0, at 31 weeks gestation comes to urgent care due to a rash on her back. Her mother first noticed a small rash on the patient's back a week ago, and it has spread despite the use of a topical cream. The patient has had no prenatal care. Vital signs are normal. Fetal heart rate is 150 /min. Fundal height is 28 cm. The rash extends across her trunk and extremities, including the palms of the hands and the soles of the feet. The lesions do not bleed, and there are no excoriations. The rash is seen in the image below, with similar lesions on the palms and soles:
Show Explanatory Sources
Which of the following is the most likely diagnosis in this patient?
Syphilis manifestations | |
Primary |
|
Secondary |
|
Latent |
|
Tertiary |
|
CNS = central nervous system. | |
This patient's maculopapular rash involving the trunk, extremities, and soles is most likely due to secondary syphilis. Primary syphilis typically causes a painless genital chancre (ie, inoculation site) that can often go unnoticed. Untreated, primary syphilis progresses within weeks to months to secondary syphilis, which typically causes a diffuse maculopapular rash due to the widespread circulation of Treponema pallidum. The rash usually begins along the skin-cleavage lines of the trunk and extends to the extremities, including the palms and soles.
Because T pallidum crosses the placenta, patients are at increased risk for obstetric complications, including fetal growth restriction, as possibly demonstrated by this patient's lagging fundal height of 28 cm at 31 weeks gestation. Other complications include congenital infection and possible intrauterine fetal demise. Therefore, all pregnant patients are screened for syphilis at the initial prenatal visit; repeat third-trimester screening is indicated in patients with risk factors (eg, HIV) or limited or no prenatal care, such as this patient. Those testing positive are treated with intramuscular penicillin G benzathine.
(Choice A) Intrahepatic cholestasis of pregnancy can present in the third trimester with generalized pruritus that is worse on the palms and soles. Although these patients can have excoriations from scratching, there is no rash.
(Choice B) Pityriasis rosea is a pruritic, papulosquamous rash that often follows a viral illness. Although it can begin on the back and spread in a similar pattern along the lines of skin-cleavage, it does not involve the palms or soles.
(Choice C) Polymorphic eruption of pregnancy can present as pruritic, erythematous papules in the third trimester; however, this rash starts within the abdominal striae, and the palms and soles are spared.
(Choice E) Tinea versicolor, a fungal skin infection caused by Malassezia species, can present with hypo- or hyperpigmented macules on the trunk or extremities; however, the palms and soles are typically spared.
Educational objective:
Secondary syphilis causes a diffuse maculopapular rash along the skin-cleavage lines of the trunk (ie, Christmas tree pattern) that extends to the extremities, including the palms and soles.