Sequential assessment of an antidrug antibody response in a patient with a systemic delayed-onset sulphonamide hypersensitivity syndrome reaction

A 19-year-old man was treated with trimethoprim-sulphamethoxazole intermittently over 4 weeks. He developed a rash and fever. Despite treatment with low-dose methylprednisolone, his condition worsened. He developed a confluent erythematous macular eruption, elevated liver enzymes, lymphadenopathy, polyserositis and eosinophilia. A tentative diagnosis of sulphonamide hypersensitivity syndrome reaction (SHSR) was made and a serum sample (acute) was obtained to screen for antibodies associated with SHSR. Intravenous methylprednisolone sodium succinate (250 mg every 6 h for 48 h) was administered. The patient's condition improved, and he was discharged with oral prednisone. A convalescent serum sample was obtained 14 weeks later. By Western blotting and enzyme-linked immunosorbent assay (ELISA), antisulphamethoxazole IgG antibodies were detected in the acute serum sample, supporting the clinical diagnosis of SHSR. Contrary to expectations, antibodies were not detected in the convalescent serum sample by immunoblotting. Antisulphamethoxazole antibodies were detected by ELISA in the convalescent serum, but the titre was decreased approximately 45-fold. One possible explanation for the decrease in antibody concentration in the convalescent sample was the administration of high-dose glucocorticoids to the patient following collection of the acute serum sample.