Approach to viral exanthems (pediatrics): Clinical sciences

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. 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 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.

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.

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.

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. 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.