Derm Dx: A diffuse erythematous rash that blanches with pressure


  • CA0311ScarletFever_Tongue

  • CA0311ScarletFever_Chest

  • CA0311ScarletFever_Abdomen

  • CA0311ScarletFever_Arm

  • CA0311ScarletFever_Back

An 8-year-old child presents with a diffuse erythematous made up of punctate popular elevations the size of pinheads that blanche with pressure. The rash began with flushing of the cheeks and forehead and rapidly spread to the trunk and extremities, where it is most marked on the inguinal, axillary, antecubital and abdominal areas.

Rash onset occurred about one day after the child developed pharyngitis accompanied by a high-grade fever and flu-like symptoms. What’s your diagnosis?

Submit your answer and read the full explanation below. If you like this activity or have a suggestion, tell us about it in the comment box at the bottom of the page.

Scarlet fever is a diffuse erythematous eruption mediated by pyrogenic exotoxin that is produced and circulated following a pharyngeal infection with group A streptococci. Fewer than 10% of "strep throat" cases result in scarlet fever.Although most cases of scarlet fever...

Submit your diagnosis to see full explanation.

Scarlet fever is a diffuse erythematous eruption mediated by pyrogenic exotoxin that is produced and circulated following a pharyngeal infection with group A streptococci. Fewer than 10% of “strep throat” cases result in scarlet fever.

Although most cases of scarlet fever occur after group A beta-hemolytic streptococcal replication in the throat and tonsils, clinically indistinguishable forms of the rash can develop after streptococcal infection of the skin and soft tissue, surgical wounds or the uterus.

Group A streptococcal scarlet fever is contagious, and person to person transmission can occur from a patient overtly infected or an asymptomatic carrier via airborne fomites.

Patients who have been infected experience a one-to-four day incubation period followed by sudden onset of fever accompanied by symptoms including sore throat, headache, nausea, vomiting, abdominal pain, myalgias, and malaise. The characteristic rash appears 12 to 48 hours after fever, first as erythematous patches below the ears, on the chest and axilla and disseminates to the trunk and extremities over the course of 24 hours.

Fever peaks on the second day and can last as long as a week in untreated patients, but generally abates in one to two days with antibiotic treatment.

As the rash progresses it may resemble sunburn with goosepimples and the skin may have a rough, sandpaperlike texture. Patient may have circumoral pallor. Miliary sudamina can occur on the abdomen, hands, and feet in severe cases. The rash resolves in one week and is followed by desquamation that can last as long as seven weeks.

Scarlet Fever is most common in children aged 4 to 8 years. By the age of 10 years, 80% of children develop type-specific immunity to the prevalent serotypes. The course of illness is most often benign; however certain rare nephritogenic strains of group A beta-hemolytic streptococci can result in glomerulonephritis or toxic streptococcal syndrome.

Other complications can include rheumatic fever, cervical lymphadenitis, otitis media, peritonsillar abscess, sinusitis, bronchopneumonia, meningitis, brain abscess, intracranial venous sinus thrombosis, septicemia, hepatitis, vasculitis and uveitis.


Throat culture is the gold standard for confirming upper respiratory group A streptococcal infection, with an approximate 90% sensitivity for detecting the bacteria in the pharynx. Rapid antigen tests are also available with about a 95% specificity, and a 70% to 90% sensitivity.


Scarlet fever can be treated with penicillin or a first generation cephalosporin to shorten the course of illness, reduce the spread of illness, and to prevent rheumatic fever and suppurative complications. Clinicians can prescribe erythromycin as an alternative therapy for patients who are allergic to penicillin. Children with scarlet fever can return to school 24 hours after beginning antibiotics.


1. Freedberg IM, Isin AZ, Wolff K, et al. Fitzpatrick’s Dermatology in General Medicine (5th ed.). 1999. New York: McGraw-Hill.

2. Gerber MA et al. Circulation. Mar 24 2009;119(11):1541-51.

3. Bass JW. Pediatr Infect Dis J. Oct 1991;10(10 Suppl):S43-9. 

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