Infectious Disease · Viral Exanthems
The facts most likely to be tested
Varicella presents with a diffuse, pruritic, vesicular rash in asynchronous stages of development (papules, vesicles, and crusts present simultaneously).
The classic distribution of the rash is centripetal, starting on the face and trunk before spreading to the extremities.
Transmission occurs via respiratory droplets or direct contact with vesicular fluid, and patients are infectious until all lesions have crusted over.
The most common complication in children is secondary bacterial skin infection (usually Staphylococcus aureus or Group A Streptococcus).
Varicella pneumonia is the most serious complication in adults and immunocompromised patients, requiring prompt treatment with intravenous acyclovir.
Post-exposure prophylaxis for susceptible, high-risk individuals (e.g., pregnant women, immunocompromised) is varicella-zoster immune globulin (VZIG).
The live-attenuated varicella vaccine is routinely administered in two doses at 12–15 months and 4–6 years of age.
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A 6-year-old boy is brought to the clinic by his mother due to a rash that started 2 days ago. The patient has a low-grade fever and malaise. Physical examination reveals a diffuse, pruritic rash consisting of vesicles on an erythematous base in various stages of evolution, including fresh vesicles and dry crusts, primarily located on the trunk and face. The patient has not received his scheduled childhood vaccinations. He is otherwise hemodynamically stable.
What is the most appropriate management for this patient?
Supportive care (calamine lotion, antihistamines, and hygiene)
The patient presents with the classic asynchronous rash of varicella; in an immunocompetent child, the condition is self-limiting and requires only supportive care to prevent secondary bacterial infection.
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Etiology / Epidemiology
Caused by Varicella-Zoster Virus (VZV); highly contagious via respiratory droplets. Primarily affects unvaccinated children.
Clinical Manifestations
Classic dewdrop on a rose petal rash; asynchronous lesions in various stages of development.
Diagnosis
Clinical diagnosis; PCR is the gold standard for confirmation if presentation is atypical.
Treatment
Acyclovir for high-risk patients; avoid aspirin due to Reye syndrome risk.
Prognosis
Generally self-limiting; bacterial superinfection (Staph/Strep) is the most common complication.
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Epidemiology & Etiology
VZV is a highly transmissible DNA virus. Transmission occurs via respiratory secretions or direct contact with vesicular fluid. Peak incidence occurs in late winter and early spring among unvaccinated pediatric populations.
Pertinent Anatomy
The virus exhibits neurotropism, establishing latency in the dorsal root ganglia. Reactivation later in life manifests as herpes zoster (shingles) along a specific dermatome.
Pathophysiology
Initial infection occurs in the nasopharynx, followed by primary viremia and seeding of the reticuloendothelial system. Secondary viremia leads to the characteristic cutaneous eruption. The immune response eventually clears the virus from the skin but leaves latent reservoirs in sensory nerve ganglia.
Clinical Manifestations
Prodrome of fever and malaise precedes the rash. The hallmark is the dewdrop on a rose petal appearance: vesicles on an erythematous base. Lesions appear in crops and are asynchronous, meaning macules, papules, vesicles, and crusts coexist. Red flags include secondary bacterial skin infection, pneumonia, or encephalitis.
Diagnosis
Diagnosis is primarily clinical based on the classic rash. If confirmation is required, PCR of vesicular fluid is the gold standard. Tzanck smear showing multinucleated giant cells is historical but lacks sensitivity compared to modern molecular testing.
Treatment
Supportive care (calamine lotion, antihistamines) is sufficient for healthy children. Acyclovir is indicated for high-risk groups (adolescents, adults, chronic skin/lung disease, or those on long-term salicylate therapy). Aspirin is strictly contraindicated due to the risk of Reye syndrome.
Prognosis
Most cases resolve within 10 days. Bacterial superinfection (Group A Strep or Staph aureus) is the most common complication. Rare but severe complications include varicella pneumonia and cerebellar ataxia.
Differential Diagnosis
Impetigo: honey-colored crusts, not asynchronous
Herpes Simplex: localized, grouped vesicles
Hand-Foot-Mouth: Coxsackie virus, involves palms/soles
Contact Dermatitis: localized to exposure site
Insect bites: usually pruritic papules, not vesicular