A case of skin exam

Q: Which disease comes to mind with the following characteristics of skin rash?

• associated with pharyngitis
• diffuse erythema that blanches with pressure
• sandpaper quality to the skin 
• usually starts in the groin and armpits 
• a strawberry tongue
• palms and soles are usually spared
• Pastia's lines

Answer: Scarlet fever 

The other common name for scarlet fever is scarlatina. It is a diffuse erythematous eruption that requires prior exposure to S. pyogenes. It is a delayed-type skin reactivity to pyrogenic/erythrogenic toxin, usually types A, B, or C).

It appears as numerous small (1 to 2 mm) papular elevations with all the qualities described in the question above. The rash expands quickly to the trunk, followed by the extremities, and ultimately desquamates.

The rash is most marked in the inguinal, axillary, antecubital, and abdominal skin folds and at pressure points. Pastia's lines are linear petechial characters in the antecubital fossae and axillary folds.

With so many tips given, this question aims to emphasize that the diagnosis of scarlet fever is made clinically. However, rapid strep testing and throat culture are required to establish the association.

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References:

1. Basetti S, Hodgson J, Rawson TM, Majeed A. Scarlet fever: a guide for general practitioners. London J Prim Care (Abingdon). 2017 Aug 11;9(5):77-79. doi: 10.1080/17571472.2017.1365677. PMID: 29081840; PMCID: PMC5649319.

2. Lau SK, Woo PC, Yuen KY. Toxic scarlet fever complicating cellulitis: early clinical diagnosis is crucial to prevent a fatal outcome. New Microbiol. 2004 Apr;27(2):203-6. PMID: 15164635.

3. Hurst JR, Brouwer S, Walker MJ, McCormick JK. Streptococcal superantigens and the return of scarlet fever. PLoS Pathog. 2021 Dec 30;17(12):e1010097. doi: 10.1371/journal.ppat.1010097. PMID: 34969060; PMCID: PMC8717983.