The decision to biopsy, treat, or wait in suspected herpes encephalitis.

The availability of vidarabine for the therapy of suspected herpes simplex encephalitis presents a difficult decision for a physician as to whether to do brain biopsy, to treat blindly, or to withhold specific therapy in a patient. The choice is made more difficult because the physician must weigh four likelihoods simultaneously: namely, of the disease, of a life-threatening complication from biopsy, of a beneificial effect from vidarabine, and of a serious adverse effect from the drug. Using decision analysis, we have derived a series of threshold probabilities whereby the physician can select his own estimates of these likelihoods to arrive at a rational approach to management. When reasonable assessments are made of the risks of biopsy and of vidarabine therapy, brain biopsy is likely to be the optimal approach in the majority of patients suspected of having herpes simplex encephalitis.