Parafollicular hair bulge in human GVHD: a stem cell-rich primary target.

We sought to determine the frequency of parafollicular hair bulge involvement in human GVHD of the skin. The parafollicular bulge was recently shown by Murphy to be a target of GVHD in the minor histoincompatible mouse GVHD model. We sought a crude estimate of this frequency by studying 541 skin biopsy reports from a 5-month period at our bone marrow transplant center. We selected 170 slides for review on the basis of a prior histological diagnosis of GVHD. Of these 41 had potentially evaluable pilar units and were recut. Three cases were considered unevaluable but the remaining 38 cases all showed positive evidence of involvement of the parafollicular hair bulge. The data confirm that the parafollicular hair bulge is involved with very high frequency in acute GVHD in humans.