Infectious Disease · Viral Infections
The facts most likely to be tested
Primary HSV-1 infection typically presents as herpetic gingivostomatitis characterized by vesicular lesions on the oral mucosa and cervical lymphadenopathy in children.
Recurrent HSV-1 infection manifests as herpes labialis, commonly known as cold sores, which typically present as a prodrome of tingling or burning followed by clustered vesicles on an erythematous base at the vermilion border.
HSV-1 is the most common cause of sporadic fatal encephalitis in the United States, classically presenting with focal neurologic deficits, seizures, and altered mental status involving the temporal lobe.
The gold standard diagnostic test for HSV encephalitis is PCR of the cerebrospinal fluid (CSF), which demonstrates high sensitivity and specificity for HSV DNA.
Herpetic whitlow is a painful, erythematous infection of the finger or thumb caused by direct inoculation of HSV-1, frequently seen in healthcare workers or children with oral herpes.
Eczema herpeticum is a severe, disseminated HSV infection occurring in patients with pre-existing atopic dermatitis, presenting with monomorphic punched-out erosions.
The first-line treatment for severe HSV-1 infections, including encephalitis, is intravenous acyclovir to prevent significant morbidity and mortality.
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A 24-year-old medical student presents to the emergency department with a 3-day history of fever, headache, and personality changes. Physical examination reveals disorientation and expressive aphasia. A lumbar puncture is performed, and CSF analysis shows lymphocytic pleocytosis, elevated protein, and normal glucose. An MRI of the brain demonstrates hyperintensity in the temporal lobes.
What is the most appropriate next step in management?
Initiation of intravenous acyclovir
The clinical presentation of temporal lobe involvement and lymphocytic pleocytosis is classic for HSV encephalitis, which requires immediate empiric treatment with IV acyclovir to prevent permanent neurological damage.
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Etiology / Epidemiology
Highly contagious DNA virus transmitted via direct contact with infected secretions; seroprevalence exceeds 60% in adults.
Clinical Manifestations
Presents as grouped vesicles on an erythematous base; herpetic whitlow and herpes gladiatorum are classic presentations.
Diagnosis
PCR is the gold standard for detection; Tzanck smear shows multinucleated giant cells.
Treatment
Valacyclovir is the first-line treatment; avoid in patients with severe renal impairment.
Prognosis
Lifelong latent infection in sensory ganglia; recurrence triggered by stress, UV light, or immunosuppression.
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Epidemiology & Etiology
HSV-1 is primarily transmitted via saliva or direct contact with lesions. Most primary infections occur in childhood and remain asymptomatic. Asymptomatic shedding is a major driver of transmission in the general population.
Pertinent Anatomy
The virus establishes latency in the trigeminal ganglia. Reactivation travels down the sensory nerve axons to the dermatome, explaining the localized nature of outbreaks.
Pathophysiology
Primary infection involves viral entry into epithelial cells, causing local replication and cell lysis. The virus then migrates via retrograde axonal transport to the sensory nerve root. Reactivation occurs when the virus travels anterograde to the skin, causing the characteristic dewdrop on a rose petal appearance.
Clinical Manifestations
Primary infection often presents as gingivostomatitis in children. Recurrent outbreaks manifest as herpes labialis (cold sores). Herpes keratitis is a medical emergency presenting with a dendritic ulcer on fluorescein staining; avoid topical steroids as they worsen the infection.
Diagnosis
PCR is the most sensitive and specific diagnostic test. A Tzanck smear is a rapid, bedside test revealing multinucleated giant cells, though it lacks the sensitivity of PCR. Viral culture is rarely used due to low sensitivity.
Treatment
Oral Valacyclovir is the preferred agent for acute outbreaks. For severe or disseminated disease, intravenous Acyclovir is required. Acyclovir-induced nephrotoxicity is a risk; ensure adequate hydration. Topical antivirals are generally ineffective for oral lesions.
Prognosis
Most patients experience periodic recurrences. Eczema herpeticum is a severe, life-threatening complication in patients with atopic dermatitis. Long-term suppression with Valacyclovir may be indicated for patients with >6 recurrences per year.
Differential Diagnosis
Aphthous ulcers: lack vesicles and are not contagious
Hand, foot, and mouth disease: involves palms and soles
Impetigo: honey-colored crusts, not vesicles
Syphilitic chancre: painless, indurated ulcer
Varicella-Zoster: dermatomal distribution, not localized to lips