Exanthematous Viral Diseases
Viral exanthems are systemic infections in which a widespread skin rash (exanthem) appears together with, or after, prodromal symptoms such as fever, upper respiratory infection and swollen lymph nodes. They are caused by many virus families, including paramyxoviruses, togaviruses, parvoviruses, herpesviruses and enteroviruses.
The rash is not only the result of virus multiplying inside keratinocytes (a cytopathic effect); much of it reflects a T-cell mediated immune response to viral antigens in the small blood vessels of the dermis. At Haute-Derma, carefully identifying the rash's morphology, the sequence in which it appears and any mucosal signs (enanthem) is key to telling a viral cause apart from drug reactions (DRESS or maculopapular drug exanthem) and bacterial infections.
How Viruses Cause Skin Rashes
Spread Through the Body and Two Ways the Skin Becomes Inflamed
After entering through the respiratory or digestive tract, the virus multiplies in regional lymph nodes and causes primary and secondary viremia. Depending on the virus, the skin lesions arise through two main mechanisms:
- Direct cytopathic effect: The virus multiplies directly in epidermal cells and in the lining of small skin vessels, causing spongiosis, keratinocyte death and fluid leakage that forms vesicles or blisters (for example, varicella-zoster virus and enteroviruses).
- Immune-mediated response: CD4+ and CD8+ T cells recognize viral antigens presented by Langerhans cells and endothelial cells. Release of pro-inflammatory cytokines (IFN-γ, TNF-α, IL-1) dilates dermal vessels, makes them leaky and draws lymphocytes around them, producing a measles-like (morbilliform or maculopapular) rash (for example, measles, rubella and parvovirus B19).
Characteristic Rash Patterns
- Morbilliform (maculopapular): Pink-red flat or slightly raised spots, 2–5 mm, that tend to merge into larger patches with islands of normal skin in between.
- Scarlatiniform: Diffuse deep red rash with a rough, sandpaper-like feel that blanches under a glass slide.
- Vesiculobullous: Scattered blisters on red skin, with clear fluid that turns cloudy and crusts over when they break.
- Reticular (lace-like, livedoid): Redness arranged in a net-like pattern, mostly on the upper arms and thighs.
Our Diagnostic Approach at Haute-Derma
History and Exposure Risk:
- Vaccination history (MMR, varicella).
- Contact with a sick person in the previous 2–3 weeks.
- Medications taken in the past 8 weeks (to rule out DRESS or a maculopapular drug exanthem).
Full Clinical Examination:
- Initial assessment: Vital signs, signs of meningitis and signs of respiratory distress.
- Skin examination:
- Lesion type: maculopapular, vesicular or purpuric.
- Direction of spread: centripetal or centrifugal.
- Inside the mouth: Koplik spots, Forchheimer spots or ulcers.
Supporting Tests:
- Rapid tests and cytology: A Tzanck smear (for blistering rashes) looks for multinucleated giant cells, which confirm VZV or HSV infection.
- Microbiology and immunology:
- Serology: Tests for virus-specific IgM antibodies; a positive IgM confirms acute infection.
- Real-time RT-PCR: Amplifies viral genetic material from throat swabs, blister fluid or blood; the gold standard for diagnosing EV71, parvovirus B19 and measles.
Management and Treatment at Haute-Derma
Most viral rashes are self-limiting. Treatment is mainly supportive: relieving symptoms, preventing secondary bacterial infection and isolating the patient to stop spread.
Supportive Treatment and Skin Care
- Fever and pain control:
- Acetaminophen (paracetamol): 10–15 mg/kg per dose, every 4–6 hours for fever ≥38.5°C, up to 60 mg/kg/day.
- CONTRAINDICATED: Never give aspirin to children or teenagers with a viral infection (especially measles or chickenpox) because of the risk of Reye syndrome, which has a high death rate (acute liver failure and brain injury).
- Itch control and skin care:
- Bathe daily in clean warm water or a mild antiseptic (chlorhexidine 0.5%), pat dry gently and avoid rubbing blisters open.
- Apply a topical antiseptic (methylene blue, chlorhexidine) to broken blisters to prevent secondary staphylococcal or streptococcal infection.
- Use calamine lotion or an oral H1 antihistamine (levocetirizine, desloratadine) to relieve itch.
Antivirals and Specific Supplements
- Measles: High-dose vitamin A by age is essential (under 6 months: 50,000 IU; 6–12 months: 100,000 IU; over 12 months: 200,000 IU/day for 2 consecutive days) to help the eyes and airways recover and lower the risk of death.
- Chickenpox (varicella):
- Healthy children under 12: supportive care.
- Adults, teenagers 13 and older, or people with underlying skin disease (such as atopic dermatitis): valacyclovir 1,000 mg three times daily or acyclovir 800 mg five times daily for 7 days, ideally started within the first 24–48 hours of the rash.
