From the Research
Yes, a patient with a bilateral leg rash can still have shingles despite a negative VZV PCR test. While shingles typically presents as a unilateral rash following dermatome distribution, bilateral presentations can occur, especially in immunocompromised patients 1. VZV PCR tests have a sensitivity of 95-100% in vesicular lesions but may yield false negatives in crusted lesions or if sample collection is inadequate. The timing of testing is crucial, with optimal results when performed on fresh vesicular fluid within 3 days of rash onset.
Some key points to consider in the diagnosis and management of shingles include:
- Clinical presentation: Shingles is characterized by a painful, unilateral rash that follows a dermatomal distribution, although bilateral presentations can occur, especially in immunocompromised patients 1.
- Diagnostic testing: VZV PCR is a sensitive test for diagnosing shingles, but false negatives can occur, especially if the test is performed on crusted lesions or if sample collection is inadequate.
- Alternative diagnostic approaches: Direct immunofluorescence assay, viral culture, or Tzanck smear can be used to diagnose shingles if VZV PCR is negative.
- Treatment: Antiviral medications such as acyclovir, valacyclovir, or famciclovir can be effective in treating shingles, especially if started early in the course of the disease 2, 3.
In the context of a patient with a bilateral leg rash and a negative VZV PCR test, clinical judgment remains important, and treatment with antiviral medications should be considered if clinical suspicion is high despite negative testing, particularly in immunocompromised patients or those with severe presentations 4. The most recent and highest quality study 4 supports the use of antiviral medications in the treatment of shingles, even in cases with negative diagnostic testing.