What is the overview of viral exanthem, including its causes, symptoms, diagnosis, treatment, and prevention?

Viral Exanthems: Comprehensive Overview

Viral exanthems are common skin rashes caused by various viral infections, typically presenting as maculopapular eruptions that may be difficult to distinguish from other infectious and non-infectious causes. 1, 2

Causes

• Human herpesvirus 6 (HHV-6B) and HHV-7 are primary causes of exanthem subitum (roseola infantum), with approximately 90% of children infected by age 1 and nearly 100% by age 3 3
• Enteroviruses (coxsackievirus and echovirus) are common causes of viral exanthems that can present with petechial manifestations 2, 4
• Other viral causes include respiratory viruses, Epstein-Barr virus, parvovirus B19, measles, rubella, and human immunodeficiency virus 4, 5
• Emerging and re-emerging viral exanthems include COVID-19, chikungunya, hand-foot-and-mouth disease, and mpox 6

Clinical Presentation

Symptoms

• Fever is typically the initial symptom, often high-spiking (39-40°C) and may persist for several days before rash appearance 1
• Associated symptoms may include headache, malaise, myalgia, and upper respiratory symptoms 1
• In roseola, high fever typically lasts 3-5 days and resolves abruptly as the rash appears 3

Rash Characteristics

• Morphology varies widely and can be macular, maculopapular, papular, urticarial, vesicular, or a combination 6, 5
• Distribution patterns differ by causative virus:
  • Enteroviral rashes are typically generalized and less likely to involve palms and soles 2
  • Roseola presents with a maculopapular eruption that appears as fever resolves 3
  • Some viral exanthems may mimic bacterial infections like Rocky Mountain Spotted Fever or meningococcemia 1, 2

Age-Specific Considerations

• Certain exanthems are more common in specific age groups, which can help narrow the differential diagnosis 5
• Roseola primarily affects infants and young children under age 3 3
• Hand-foot-and-mouth disease typically affects young children but can occur at any age 6

Diagnosis

Clinical Approach

• Diagnosis is primarily clinical, based on age, distribution and morphology of the rash, and associated symptoms 5
• The timing of rash relative to fever onset can provide diagnostic clues (e.g., roseola rash appears as fever resolves) 1, 3

Laboratory Testing

• Most viral exanthems do not require laboratory confirmation in immunocompetent patients with typical presentations 5
• Consider laboratory testing in:
  • Atypical presentations
  • Immunocompromised patients
  • Pregnant women
  • Severe or prolonged illness 7
• Available tests include:
  • Serological tests for specific viral antibodies (IgM, IgG)
  • PCR detection of viral DNA/RNA in blood, throat swabs, or skin lesions 3
  • Complete blood count may show characteristic patterns (e.g., leukopenia in certain viral infections) 1

Differential Diagnosis

Infectious Causes

• Bacterial infections: meningococcemia, Rocky Mountain Spotted Fever, scarlet fever, streptococcal pharyngitis 1
• Other tickborne diseases 1
• Mycoplasma pneumoniae infection 1

Non-Infectious Causes

• Drug hypersensitivity reactions 1
• Kawasaki disease 1
• Stevens-Johnson syndrome 1
• Immune thrombocytopenic purpura 1

Treatment

General Approach

• Most viral exanthems are self-limited and require only supportive care 5
• Treatment focuses on symptom management:
  • Antipyretics for fever control
  • Adequate hydration
  • Rest 4

Specific Antiviral Therapy

• Antiviral therapy is generally not indicated for most common viral exanthems in immunocompetent hosts 3
• In immunocompromised patients with severe HHV-6 infection, ganciclovir or foscarnet may be considered 3
• Influenza-associated exanthems may benefit from early neuraminidase inhibitor therapy if identified within 48 hours of symptom onset 1

Prevention

• No vaccines are available for most causes of viral exanthems except for measles, mumps, rubella, and varicella 3
• Prevention of exposure is generally not feasible for common viral exanthems due to their ubiquity 3
• Hand hygiene and respiratory etiquette can help reduce transmission 6

Special Considerations

Red Flags Requiring Urgent Evaluation

• Rapidly progressive petechial rash (concerning for meningococcemia) 2
• High fever with petechial rash and altered mental status 1
• Mucosal involvement with severe erosions or target lesions (concerning for Stevens-Johnson syndrome) 1
• Rash with significant palmar/plantar involvement in the setting of fever (consider Rocky Mountain Spotted Fever) 1

Pregnant Women

• Certain viral exanthems pose specific risks during pregnancy, particularly parvovirus B19, rubella, measles, and varicella 8
• Prompt evaluation and specific testing are warranted in pregnant women with fever and rash 8

Immunocompromised Patients

• May present with atypical or more severe manifestations 7
• Lower threshold for diagnostic testing and consideration of specific antiviral therapy 7