This condition typically presents in the setting of Streptococcus pyogenes pharyngitis, or strep throat, and is spread via mucosal transfer in close proximity such as classrooms and nurseries. The dermatologic symptoms are a result of the endotoxin produced by S. pyogenes, which is part of the group A Strep bacteria. Clinically, the presentation can be differentiated from an allergic eruption by its relation to acute pharyngitis, insidious onset, and lack of confluence of the lesions. Diagnosis is supported by a throat culture and rapid strep test, although a rapid test lacks reliability in older patients who are less commonly affected and likely to be carriers. First-line treatment is penicillin or amoxicillin, but first-generation cephalosporins, clindamycin, or erythromycin are sufficient if the patient is allergic to penicillins. Prognosis worsens as time between onset and treatment increases, but is overall excellent now with the introduction of antibiotics and improved hygiene.
Scarlet fever is among a list of many common childhood rashes, and it can be difficult to differentiate between these pathologies on clinical presentation. A few notable childhood dermatologic eruptions include erythema infectiosum (fifth disease), roseola (exanthema subitum or sixth disease), and measles. These cases can be distinguished clinically by the age of the patient, distribution, and quality of the symptoms. Laboratory testing may be used to confirm the diagnosis.
Dr. Donna Bilu Martin
Erythema infectiosum is known as fifth disease or slapped-cheek rash because it commonly presents on the cheeks as a pink, maculopapular rash in a reticular pattern. The disease is caused by parvovirus B19 and is accompanied by low fever, malaise, headache, sore throat, and nausea, which precedes the erythematous rash. The facial rash appears first and is followed by patchy eruptions on the extremities. Appearance of the rash typically indicates the patient is no longer contagious, and patients are treated symptomatically with NSAIDs and antihistamines for associated pruritus.
Roseola infantum is commonly caused by human herpesvirus 6 and is usually found in children 3 years and younger. The defining symptom is a high fever, which is paired with a mild cough, runny nose, and diarrhea. A maculopapular rash appears after the fever subsides, starting centrally and spreading outward to the extremities. Although this rash is similar to measles, they can be differentiated by the order of onset. The rash caused by measles begins on the face and mouth (Koplik spots) and moves downward. Additionally, the patient appears generally healthy and the disease is self-limiting in roseola, while patients with measles will appear more ill and require further attention. Measles is caused by the measles virus of the genus Morbillivirus and is highly contagious. It is spread via respiratory route presenting with fever, cough, coryza, and conjunctivitis followed by the rash. Fortunately, the measles vaccine is in widespread use, so cases have declined over the years.
Our patient had a positive strep test. Influenza and coronavirus tests were negative. She was started on daily amoxicillin and the rash resolved within 2 days of taking the antibiotics.
This case and photo were submitted by Lucas Shapiro, BS, Nova Southeastern University, Tampa, and Dr. Bilu Martin.
Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at mdedge.com/dermatology. To submit a case for possible publication, send an email to dermnews@mdedge.com.
References
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Moss WJ. Lancet. 2017 Dec 2;390(10111):2490-502.
Mullins TB and Krishnamurthy K. Roseola Infantum, in “StatPearls.” Treasure Islan, Fla.: StatPearls Publishing, 2022.
Pardo S and Perera TB. Scarlet Fever, in “StatPearls.” Treasure Island, Fla.: StatPearls Publishing, 2022.