Background Epstein-Barr virus (EBV)-associated T/natural-killer lymphoproliferative disorders form a group of diseases that includes classical and systemic hydroa vacciniforme (HV) and hypersensitivity to mosquito bites (HMB). Patients with systemic HV (sHV) and HMB often have a poor prognosis, although little is known about the prognostic factors. Objectives To elucidate the prognostic factors of HV and HMB. Methods We studied clinicopathological manifestations, routine laboratory findings, anti-EBV titres, EBV DNA load and EBV-encoded gene expression, including expression of BZLF1, in 50 patients with classical HV (cHV), sHV, HMB only and HMB with HV (HMB + HV), and further analysed 30 patients who were available for follow-up. Results The median age of disease onset was 5 years (range 1-74). A follow-up study indicated that fatal outcomes were observed in three of eight patients with sHV, two of six patients with HMB only, and two of five patients with HMB + HV. The main causes of death were complications from haematopoietic stem-cell transplantation and multiorgan failure. There were no fatalities among the 11 patients with cHV. Univariate analysis revealed two poor prognostic indicators: (i) onset age > 9 years and (ii) the expression of an EBV-encoded immediate-early gene transcript, BZLF1 mRNA, in the skin lesions (P < 0·001 and P = 0·003, respectively). Conclusions No prognostic correlation was observed in EBV-infected lymphocyte subsets, anti-EBV antibody titres or EBV DNA load. Late onset and EBV reactivation are both related to more severe phenotypes of the disease, and thus may predict a poor prognosis.
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