A 28-year-old woman presents with severe vesicular rash on the genitals, fever, and dysuria for 3 days. She has a history of similar episodes. Tzanck smear shows multinucleated giant cells. Which is the most appropriate confirmatory investigation?

Explanation

## Investigation of Choice for HSV Confirmation ### Why PCR is the Gold Standard **Key Point:** PCR (polymerase chain reaction) for HSV-1 and HSV-2 is the most sensitive and specific confirmatory test for genital herpes, especially in recurrent episodes. It can differentiate between HSV-1 and HSV-2, which has prognostic and counselling implications. **High-Yield:** PCR has >95% sensitivity and specificity, works on multiple specimen types (vesicular fluid, swabs, CSF, tissue), and provides rapid results (within 24–48 hours in most labs). ### Why Other Options Are Suboptimal | Investigation | Limitation | |---|---| | **Viral culture** | Requires 3–7 days; less sensitive in recurrent disease; labour-intensive; not routinely available | | **DFA** | Rapid (2–4 hours) but less sensitive (~80%) than PCR; operator-dependent; cannot differentiate HSV-1 from HSV-2 | | **Serology (IgM/IgG)** | IgM unreliable in recurrent episodes; IgG indicates past infection, not acute disease; cannot confirm active infection | **Clinical Pearl:** In recurrent genital herpes (as suggested by "history of similar episodes"), IgM is often negative because the patient is already seropositive. Serology is useful only for primary HSV infection or epidemiological screening. **Tip:** Tzanck smear is a rapid screening tool (shows multinucleated giant cells, ballooning degeneration) but is NOT confirmatory — it cannot differentiate HSV from VZV. Always follow with PCR or DFA for definitive diagnosis.