Urticarial Rash Following Sore Throat
A urticarial rash developing after a sore throat is most likely caused by a streptococcal pharyngitis infection, and you should obtain a throat culture and streptococcal antibody testing (Streptozyme) to confirm the diagnosis, then treat with appropriate antibiotics if positive. 1
Likely Etiology
The temporal association between sore throat and urticaria strongly suggests an infectious trigger:
Streptococcal pharyngitis is a well-documented cause of acute urticaria, with studies showing that 13 of 32 screened cases (approximately 40%) had either positive throat cultures or significant streptococcal exoenzyme antibodies. 1
The streptococcal infection may not always be clinically apparent at the time urticaria develops, making laboratory confirmation essential rather than relying solely on clinical pharyngitis symptoms. 1
Viral infections are also common triggers of acute episodic urticaria in both children and adults, representing one of the most frequent causes alongside allergic reactions to foods and drugs. 2
Diagnostic Approach
For acute urticaria following sore throat, perform targeted testing rather than extensive workups:
Obtain a throat culture for Group A Streptococcus. 1
Measure streptococcal exoenzyme antibodies (Streptozyme test) to detect recent or ongoing streptococcal infection. 1
No additional laboratory investigations are required for typical acute urticaria unless the history suggests specific triggers such as food allergens, drug reactions, or physical stimuli. 3, 4
The diagnosis of urticaria itself is primarily clinical, characterized by pruritic wheals that last 2-24 hours per individual lesion and resolve without scarring. 4
Management Strategy
First-line treatment consists of:
Non-sedating second-generation H1 antihistamines at standard doses are the cornerstone of acute urticaria management. 4, 5, 6
If streptococcal infection is confirmed, initiate appropriate antibiotic therapy (typically penicillin or amoxicillin for streptococcal pharyngitis). 1
Adjunctive measures when needed:
A short course of oral corticosteroids can shorten the duration of acute episodes, though this should be brief (e.g., 3 days at appropriate dosing). 4
Topical cooling agents such as calamine lotion or 1% menthol in aqueous cream provide symptomatic itch relief. 4
Avoid aspirin and NSAIDs, as these can provoke mast cell degranulation and worsen urticaria through leukotriene formation and histamine release. 3, 4
Critical Pitfall to Avoid
Do not discontinue antibiotic therapy if urticaria develops during treatment of confirmed streptococcal infection. One case report suggests that stopping antibiotics when urticaria appears, even though it may seem necessary, is likely inappropriate. 1 The urticaria can be managed symptomatically with antihistamines while continuing the necessary antimicrobial therapy.
When to Escalate Care
Immediate intramuscular epinephrine is required if:
Laryngeal angioedema develops (swelling of lips, tongue, or throat with difficulty breathing). 4, 2
Signs of anaphylaxis appear (respiratory distress, hypotension, or multi-system involvement). 4, 2
Parenteral hydrocortisone may be added as an adjunct for severe laryngeal edema, though its effect is delayed. 4