What could cause a rash to occur two weeks after having strep (streptococcal) throat?

Rash Occurring Two Weeks After Strep Throat: Causes and Management

A rash occurring two weeks after strep throat is most likely post-streptococcal glomerulonephritis (PSGN), a non-suppurative complication of group A streptococcal pharyngitis that typically manifests after a latency period of a few weeks. 1

Common Post-Streptococcal Complications

Non-Suppurative Complications

• Acute rheumatic fever: Occurs 2-3 weeks after pharyngeal infection with group A streptococcus 2
• Post-streptococcal glomerulonephritis: Follows group A streptococcal pharyngitis after a latency period of 1-3 weeks 1, 3
• Post-streptococcal reactive arthritis: Typically occurs within 10 days of group A streptococcal infection 4

Clinical Presentation of Post-Streptococcal Rashes

• Maculopapular rash that may become petechial 1
• Erythema marginatum (characteristic of acute rheumatic fever) 2
• Erythematous skin rash (particularly common in patients with mononucleosis who receive amoxicillin) 5

Pathophysiology

• PSGN is an immune complex-mediated disease where streptococcal antigens trigger immune complex deposition in glomerular tissue 3
• Immune complexes activate the alternate complement pathway, resulting in inflammation 6
• The latency period (1-3 weeks) represents the time needed for antibody formation and immune complex deposition 3, 6

Diagnostic Considerations

Laboratory Findings

• Low C3 complement levels (hallmark finding of PSGN) 3
• Elevated anti-streptolysin O (ASO) titers 3
• Urinalysis showing hematuria and proteinuria in PSGN 3

Clinical Assessment

• Evaluate for features of acute nephritic syndrome (hematuria, proteinuria, hypertension, edema) 3, 6
• Check for other post-streptococcal complications (cardiac manifestations, arthritis) 1, 2
• Assess for hypertension and signs of fluid overload 3

Management Approach

Immediate Management

• Treat with penicillin (or erythromycin if penicillin-allergic) even if no active infection is present to decrease antigenic load 3
• If penicillin V is indicated, administer twice or three times daily for 10 days 1

For Post-Streptococcal Glomerulonephritis

• Restrict dietary sodium intake 3
• Manage hypertension with diuretics and antihypertensive medications 3
• Monitor for fluid overload and treat with diuretics if necessary 3
• Regular assessment of kidney function, blood pressure, proteinuria, and hematuria 3

For Acute Rheumatic Fever

• Prevention depends on effective control of group A streptococcal pharyngitis 1
• Secondary prophylaxis with antibiotics is important for patients at high risk 1, 7

Special Considerations

• Concomitant occurrence of both acute rheumatic fever and PSGN is rare because they typically result from different serotypes of Group A beta-hemolytic Streptococcus 7, 8
• Patients with a history of valvular heart disease or rheumatic fever are at increased risk for complications 1
• Most cases of PSGN in children make a full recovery, but some may develop persistent proteinuria, hypertension, or progress to chronic kidney disease 6

Prognosis

• Complications of group A β-haemolytic streptococcal pharyngitis are generally rare in both children and adults 1
• PSGN typically has good outcomes with appropriate supportive care 3, 6
• Pharyngeal carriers of group A streptococci show an extremely low risk of post-streptococcal complications 1