Widespread unilateral pain associated with herpes simplex virus infections

We describe a patient group with unexplained widespread pain on one side of the body and pain exacerbations during active labial or genital herpes and during herpetic central nervous system infections. The patients had no visible lesion of the central nervous system on magnetic resonance imaging or abnormality in electrophysiological studies. To understand the nature of the pain and its possible relation to herpes simplex virus (HSV) infections, a clinical neurological examination was performed and quantitative sensory testing and skin biopsies were assessed in 17 patients. The levels of serum total immunoglobulins and IgG subclasses and the frequencies of the immune response genes at the IGH@, HLA-A, -B, -DRB1, C4A, and C4B loci were analyzed in the patients and in control subjects. The patients manifested a uniform clinical syndrome with unilateral pain that was best described as neuropathic and that was exacerbated by HSV reactivations. Low plasma IgG3 concentrations, the presence of either low plasma IgG1 or IgG3 or both, and high anti-HSV-2-IgG titers were more common in the patients than in the control subjects, which rendered the patients more vulnerable to HSV recurrences. Perspective: We suggest that low immunoglobulin subclass levels and certain MHC alleles render the patients susceptible to recurring HSV infections. HSV reactivations and the accompanying inflammatory process cause dysfunction of the central nervous system that manifests as neuropathic pain. Studies using functional brain imaging are needed to clarify this syndrome. (C) 2008 by the American Pain Society.