What is the differential diagnosis and management for a pediatric patient presenting with a sandpaper rash?

Differential Diagnosis of Pediatric Sandpaper Rash

Scarlet fever is the primary diagnosis to consider when a child presents with a sandpaper-textured rash, caused by group A streptococcal toxins (superantigens) that typically affects children aged 5-15 years. 1, 2

Life-Threatening Conditions to Rule Out First

Rocky Mountain Spotted Fever (RMSF)

• Petechial or purpuric elements on a sandpaper-like rash demand immediate doxycycline administration, regardless of age, as mortality increases from 0% when treated by day 5 to 33-50% when delayed to days 6-9. 3, 4
• Palm and sole involvement is pathognomonic and requires urgent action 3, 4
• Thrombocytopenia, elevated hepatic transaminases, and hyponatremia support this diagnosis 3, 4
• Up to 40% report no tick bite history 4

Meningococcemia

• Petechial or purpuric rash with systemic toxicity (hypotension, altered mental status, respiratory distress) constitutes a medical emergency 3, 4
• Half of children are sent home at first presentation, making 24-hour reassessment mandatory for any febrile child with rash 5, 3

Most Common Diagnosis: Scarlet Fever

Clinical Presentation

• Sandpaper-textured, erythematous, papular rash that develops on the upper trunk then spreads throughout the body, characteristically sparing palms and soles 1, 6, 2
• Associated with sore throat, fever, and strawberry tongue 1
• Caused by group A streptococcal superantigens in children aged 5-15 years 1, 2

Diagnostic Workup

• Throat culture or rapid strep test 1
• If red flags present: CBC with differential, CRP, comprehensive metabolic panel, blood culture before antibiotics 3, 4

Treatment

• Penicillin or amoxicillin for 10 days (first-line) 7
• Azithromycin or cephalosporins for penicillin-allergic patients 7
• Early treatment prevents serious complications including acute rheumatic fever, glomerulonephritis, bacteremia, pneumonia, endocarditis, and meningitis 1

Other Differential Diagnoses

Atopic Dermatitis (Eczema)

• Chronic, relapsing inflammatory condition with itchy skin and scratching behavior 5, 8
• Requires three of: history of itchiness in skin creases, history of asthma/hay fever in first-degree relatives, general dry skin, visible flexural eczema, onset in first two years of life 5, 8
• Deterioration in stable eczema suggests secondary bacterial infection (look for crusting/weeping) or contact dermatitis 5, 8
• Staphylococcus aureus infection commonly complicates eczema 5

Impetigo

• Highly contagious superficial bacterial infection caused by β-hemolytic Streptococcus and/or S. aureus 8, 7
• Presents as discrete purulent lesions, most commonly affecting face and extremities 8, 6
• Requires topical or oral antibiotics (mupirocin, cephalosporins, or beta-lactamase-stable penicillins) 7

Viral Exanthemas

• Roseola: High fever for 3-4 days followed by rose-pink maculopapular rash appearing precisely when fever breaks 4, 6
• Erythema infectiosum (fifth disease): "Slapped cheek" appearance with viral prodrome 6
• These often mimic drug reactions when medications are given during viral illness 9

Immediate Management Algorithm

Step 1: Assess for Life-Threatening Features

• If petechiae/purpura, palm/sole involvement, or systemic toxicity present: Start doxycycline immediately (even in children <8 years), obtain blood cultures, and hospitalize urgently 3, 4

Step 2: Evaluate for Scarlet Fever

• Examine for sandpaper rash sparing palms/soles, pharyngitis, and strawberry tongue 1, 6
• Obtain throat culture/rapid strep test 1
• Start penicillin or amoxicillin if positive 7

Step 3: Consider Secondary Bacterial Infection

• Look for crusting, weeping, or purulent lesions suggesting impetigo or infected eczema 5, 8
• Send bacterial swabs if infection suspected 5
• Treat with appropriate antibiotics (beta-lactamase-stable penicillins or cephalosporins) 7

Step 4: Mandatory Reassessment

• Schedule follow-up within 24 hours for any child sent home, as serious infections are frequently missed at first presentation 5, 3

Critical Pitfalls to Avoid

• Never dismiss a sandpaper rash without considering scarlet fever and RMSF 3, 1
• Do not delay doxycycline if RMSF is suspected—each day of delay dramatically increases mortality 3, 4
• Absence of tick bite history does not exclude RMSF 4
• Viral exanthema and drug reactions are diagnoses of exclusion after ruling out bacterial causes 9
• Deteriorating eczema requires evaluation for secondary infection, not just increased steroids 5, 8