Varicella-zoster virus infections: The Daily PANCE Blueprint
A 65-year-old man presents to the clinic with a painful, vesicular rash on his left thoracic region that wraps around to the midline. He reports that the rash started as a burning sensation 3 days ago before the vesicles appeared. He has a history of chickenpox as a child but no significant medical history otherwise. He denies any recent illness or immunosuppressive therapy. Which of the following is best for confirming herpes zoster infection?
A. PCR testing of vesicle fluid
B. Complete blood count with differential
C. Skin biopsy
D. Tzanck smear
E. MRI of the affected dermatome
Answer and topic summary
The answer is A. PCR testing of vesicle fluid
PCR (Polymerase Chain Reaction) testing of vesicle fluid is the most accurate diagnostic method for confirming herpes zoster infection. Herpes zoster, also known as shingles, is caused by the reactivation of the varicella-zoster virus (VZV). PCR testing is highly sensitive and specific for detecting VZV DNA in vesicle fluid, making it a valuable tool for confirming the diagnosis in clinically ambiguous cases or when specific antiviral treatment is considered, especially in immunocompromised patients.
B. Complete blood count with differential – While a CBC with differential can help assess the overall health status and detect signs of infection or immunosuppression, it is not specific for diagnosing herpes zoster infection.
C. Skin biopsy – A skin biopsy can be useful for histopathological examination to confirm herpes zoster infection, especially in atypical cases. It can demonstrate changes associated with VZV infection but is more invasive than PCR testing of vesicle fluid and not typically the first diagnostic step.
D. Tzanck smear – The Tzanck smear can be used to detect multinucleated giant cells typical of herpesvirus infections, including herpes simplex and varicella-zoster virus. However, it lacks specificity and sensitivity compared to PCR testing and cannot distinguish between different types of herpesvirus infections.
E. MRI of the affected dermatome – MRI is not a standard diagnostic tool for herpes zoster. It may be used in rare cases to assess complications or involvement of the central nervous system, but it is not part of the routine workup for a suspected herpes zoster infection.
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Covered under ⇒ PANCE Blueprint Dermatology ⇒ ⇒ =>
Also covered as part of the Pediatric EOR and Internal Medicine EOR topic lists
