Criteria for Performing PCR in Cases of Suspected Herpes Encephalitis

We applaud the effort of Tang et al. to establish criteria for the optimal utilization of PCR for the diagnosis of herpes simplex virus (HSV) encephalitis (4). However, we are hesitant to utilize their criteria because of the rare presentation of HSV encephalitis in patients with normal cerebrospinal fluid parameters (estimated to be 2 to 3% of cases) (3). Failure to perform PCR on a patient with this presentation would put the laboratorian in an adverse medicolegal position. Furthermore, patients with early encephalitis, and presumably with normal cerebrospinal fluid parameters, are the patients in whom early intervention could provide the potential for optimal outcome.

The criterion at Charity Hospital in New Orleans, La., for referring specimens for PCR is that clinical suspicion of HSV encephalitis is high enough that the patient has been empirically started on acyclovir. Generally, therapy based on clinical suspicion of HSV encephalitis is recommended (2). A negative HSV PCR result with cerebrospinal fluid could be used in the appropriate clinical setting to support the discontinuation of acyclovir. The laboratory director consults with the primary care physician upon receipt of a request for performance of PCR, to explain the criterion. This policy ensures that therapy is instituted early in the course of the disease, when the likelihood of an optimal outcome is better. In the past 6 months, we have referred only 10 of 24 specimens for performance of PCR for HSV, saving the hospital $2,800.00.

Ed. Note: The authors of the published article did not respond.