Approach to viral exanthems (pediatrics): Clinical sciences

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Introduction0:00–0:26

A viral exanthem is a widespread rash due to a viral infection. Most viral exanthems in children are associated with mild, self-limited illnesses, but some may indicate a serious or chronic disease.
They can be categorized based on the rash morphology, which can be maculopapular, reticulated, papular, or vesicular. When a child presents with a chief concern suggesting a viral exanthem, obtain a focused history and physical exam.

Focused H&P0:26–1:21

Ask about known exposures to sick individuals, and review their immunization records. As patients or caregivers describe the rash, be sure to ask where the first lesions were seen; whether the rash is painful, pruritic, or asymptomatic; and determine the pattern in which it has spread.
Finally, ask about other symptoms, like fever, malaise, rhinorrhea, or sore throat. On exam, assess the appearance and distribution of the skin lesions, and look for mucous membrane involvement, lymphadenopathy, or conjunctival injection.
With this information, consider a viral exanthem and assess rash morphology. Let’s first look at maculopapular rash.

Maculopapular rash1:21–1:45

Maculopapular rashes consist of flat red spots called macules, as well as small raised bumps, called papules. They should make you consider measles, rubella, roseola, HIV, and infectious mononucleosis.

Measles1:45–3:22

Let’s start with measles, also called rubeola. This highly contagious infection typically occurs in under-immunized individuals.
It usually begins with the 3 C’s, which are cough, coryza, and conjunctivitis but some also report photophobia. Later on, there’s a high fever and a rash that starts behind the ears and spreads down toward the toes.
The exam will reveal a morbilliform rash, which is a bright red maculopapular rash that becomes confluent as it spreads caudally, and it may involve the palms and soles.
An early finding in measles is Koplik spots on the buccal mucosa, which consist of tiny bluish-gray spots with a white or pale center, on an erythematous base.
You won’t always see them because Koplik spots disappear when the rash appears. Based on these findings, order a measles serology or RNA PCR.
Positive measles IgM or PCR confirms the diagnosis. Here’s a clinical pearl!
Complications associated with measles range from mild to severe. Common ones include otitis media, pneumonia, and diarrhea.
More serious neurologic complications, such as acute disseminating encephalomyelitis, present during or just after an acute infection; while others, like subacute sclerosing panencephalitis, may appear several years after the infection.

Rubella3:22–4:23

Let’s switch gears and discuss Rubella. These patients are typically under-immunized, and most experience a mild illness lasting 3 to 5 days.
Symptoms usually begin with a low-grade fever, headache, and upper respiratory infection symptoms, followed by a rash on the face that spreads downward to the trunk.
The exam reveals a faint, generalized, maculopapular rash that spares the palms and soles; and possibly posterior auricular and suboccipital lymphadenopathy, which might appear before the rash.
Keep in mind that patients are most infectious when the rash is present. There might be mild conjunctival injection, or tiny palatal petechiae, called Forchheimer spots.
Next, order a rubella serology. A positive rubella IgM confirms the diagnosis.

Roseola4:23–5:14

Next up, roseola infantum is an infection caused by human herpesvirus 6. Affected children are typically between 6 and 18 months of age.
History reveals 3 to 5 days of high fever, which often triggers febrile seizures. Occasionally, patients have mild upper respiratory infection symptoms, but many are asymptomatic.
After the fever resolves, they develop a rash. On exam, there is a diffuse, pink to red maculopapular rash that starts on the trunk and progresses to the neck and extremities.
With these findings, you can make a clinical diagnosis of roseola infantum, also called exanthem subitum. Let’s move on to acute HIV infection.

HIV5:14–6:23

These patients might develop a flu-like illness with fever, headache, malaise, and sore throat. Some might report nausea, vomiting, and diarrhea, or even a history of chronic candidiasis.
Physical exam typically reveals generalized lymphadenopathy and a diffuse, non-pruritic, erythematous maculopapular rash.
Based on these findings, order HIV ELISA antibody testing; p24 antigen; and an HIV RNA PCR. If ELISA antibodies are negative, the p24 antigen is positive, and PCR reveals more than 50,000 copies of HIV RNA per milliliter, that’s acute HIV infection.
Here’s a clinical pearl! HIV may cause a rash during early infection when ELISA antibodies are still undetectable.
After 3 to 4 weeks of infection, the ELISA antibodies will also be positive. Last up is infectious mononucleosis, which is caused by Epstein-Barr virus, or EBV.

Infectious mononucleosis6:23–7:38

Affected patients are often adolescents who report fever, profound fatigue, sore throat, and possibly known exposure. Physical exam reveals pharyngeal erythema and enlarged tonsils with exudate, sometimes with visible palatal petechiae.
Additionally, you’ll often find anterior and posterior cervical lymphadenopathy, splenomegaly, and a diffuse maculopapular rash, although occasionally the rash is urticarial.
In this situation... order a monospot test and EBV anti-VCA IgM levels, which if positive, confirm the diagnosis of infectious mononucleosis.
Here’s another clinical pearl! Administering ampicillin or amoxicillin to patients with EBV infection can also induce a diffuse, pruritic, reddish-brown maculopapular rash, which does not indicate a true drug hypersensitivity reaction.

Reticulated rash/Erythema infectiosum7:38–9:00

Let’s now look at reticulated and papular rashes. Okay, time to discuss reticulated rashes that appear as flat, lacy, net-like patches on the skin.
This rash should make you consider Erythema infectiosum, which is caused by parvovirus B19. Patients might have prodromal symptoms, like fever, headache, malaise, and myalgia, followed by a rash.
Physical exam reveals a "slapped cheek" appearance with circumoral pallor in the early stage of infection. After the facial rash fades, they usually develop a classic lacy, reticulated rash on the trunk and extremities, which may last for weeks.
The exam might reveal conjunctivitis and pharyngitis. Based on these findings, make a clinical diagnosis of erythema infectiosum, which is commonly called fifth disease.
Here’s a high-yield fact! In patients with sickle cell disease or other disorders of red blood cell production, parvovirus can trigger transient aplastic anemia, while in pregnant individuals, it can cause fetal hydrops or fetal loss.
In these cases, you may decide to confirm parvovirus infection with serum IgM levels or viral DNA testing. Let’s switch gears and discuss papular rashes, which consist of small raised bumps.

Papular rash/Gianotti-Crosti syndrome9:00–10:15

In this case, consider Gianotti-Crosti syndrome, which is also called papular acrodermatitis. History typically reveals a recent viral infection, such as EBV or hepatitis B known as HBV, after which the child developed a diffuse pruritic rash lasting for several weeks.
Physical exam reveals red or flesh-colored papules on the face, buttocks, and extensor surfaces of the extremities, in a symmetrical pattern.
These findings are highly suggestive of Gianotti-Crosti syndrome. You can consider ordering EBV or HBV serology.
Elevated viral titers support a diagnosis of Gianotti-Crosti syndrome. Here’s a high-yield fact!
Another common rash that presents with papules is Molluscum contagiosum. This highly contagious but benign skin infection is caused by a poxvirus, and presents as small flesh-colored, umbilicated papules, most often in toddlers or young children.

Vesicular rash10:15–10:22

Alright, let’s discuss vesicular rashes, which are characterized by small fluid-filled blisters. Starting with varicella infection or chickenpox, which is usually seen in under-immunized or incompletely immunized children after exposure.

Varicella10:22–12:00

Caregivers may report a prodrome of fever and malaise, followed by an intensely pruritic rash. Skin lesions begin as small red papules which evolve into vesicles containing clear fluid that becomes cloudy.
The rash typically spreads in a centripetal progression, from the trunk outward to the extremities. Physical exam reveals a classic "dew drop on a rose petal" rash, with clusters of vesicles in multiple stages of healing.
And sometimes, you may find lymphadenopathy. With these findings, make a clinical diagnosis of primary varicella infection.
If you’re not sure, you can send vesicular fluid for a varicella-zoster virus DNA PCR, which if positive, confirms your diagnosis.
Time for some more clinical pearls! Primary varicella infection is often complicated by secondary bacterial skin infections, such as impetigo and staphylococcal scalded skin syndrome.
In rare cases, varicella can infect the central nervous system and cause encephalitis or meningitis. For all suspected or confirmed cases of varicella, avoid aspirin use, as it can trigger Reye syndrome in patients with active infection.
Let’s finish with hand-foot-mouth disease, which is caused by coxsackievirus. This illness usually occurs in toddlers and young school-age children and presents with mildly to moderately painful mouth lesions.

Hand-foot-mouth disease12:00–13:11

Additionally, some children develop a vesicular rash on the palms of their hands and the soles of their feet. Now that name “hand foot mouth” starts to make a lot of sense.
Examination of the oral mucosa reveals shallow ulcers on an erythematous base, and you may detect a vesicular rash on the hands, feet, and occasionally, on the buttocks, but they left that out of the title.
If you see these findings, that’s hand-foot-mouth disease. Here’s one final clinical pearl!
Herpetic gingivostomatitis presents with an enanthem consisting of oral vesicles and ulcers, which can mimic the mouth lesions in hand-foot-mouth disease.
However, oral ulcers are usually limited to the oral mucosa and are exquisitely painful, with affected patients often exhibiting drooling and decreased oral intake.
Alright, as a quick recap… A viral exanthem is a widespread rash due to a viral infection. Maculopapular rashes suggest infections like measles, rubella, roseola, acute HIV infection, or infectious mononucleosis.

Review13:11–13:43

A reticulated rash suggests erythema infectiosum, while a papular rash may indicate Gianotti-Crosti syndrome. Finally, vesicular rashes could indicate primary varicella or hand-foot-mouth disease.