Do antineutrophil cytoplasmic antibodies (ANCA) play a key role in neutrophilic dermatoses? A case of propylthiouracil-induced neutrophilic dermatosis with positive perinuclear ANCA.

We report a case of neutrophilic dermatosis caused by propylthiouracil (PTU), with positive perinuclear antineutrophil cytoplasmic antibodies (p-ANCA). PTU is well known to cause vasculitis associated with positive ANCA titres, and this typically occurs late in the treatment (after months to years). PTU rarely causes neutrophilic dermatoses (three case reports). In the three cases described, ANCA was positive at the outset. Our patient's initial ANCA testing was negative and her positive p-ANCA evolved. This may be because PTU binds to myeloperoxidase (MPO) inside neutrophils, altering its configuration and thus causing antibody formation to this abnormal MPO-PTU configuration, which would not be detected by standard laboratory techniques. ANCA has been implicated in spreading neutrophil activation and thus its pathogenic effect and clinical significance may extend beyond the realm of vasculitis alone.