Abstract: 【Abstract】 Objective To analyze the clinical characteristics of Pneumocystis pneumonia （PCP） in patients with drug-induced hypersensitivity syndrome （DIHS）, and to identify factors influencing the development of PCP in patients with DIHS. Methods Patients with DIHS accompanied by PCP who were hospitalized at Department of Dermatology, Peking Union Medical College Hospital from January 2019 to August 2024 were collected, and their demographic characteristics, clinical manifestations, laboratory tests, and treatment data were retrospectively analyzed. A matched control group of DIHS patients without PCP was selected based on sex, age （± 3 years）, and disease severity at a ratio of 2∶1. Comparisons between groups were made using the independent samples t-test, Mann-Whitney U test, and Fisher's exact test. Results Eight patients with DIHS accompanied by PCP were enrolled, aged 62.38 ± 20.74 years, including 5 males and 3 females. All DIHS cases were categorized as severe, and high-dose corticosteroids were applied in the treatment of DIHS, with 7 cases additionally receiving intravenous immunoglobulins, immunosuppressants, biologic agents, or Janus kinase inhibitors. During the corticosteroid tapering, 8 patients experienced recurrences of DIHS, and 6 patients exhibited reactivation of viruses, with cytomegalovirus （CMV） as the most common virus. All the patients presented with cough and dyspnea when PCP occurred, and the diagnosis of PCP was confirmed by the presence of Pneumocystis jirovecii DNA in sputum or bronchoalveolar lavage fluid. Seven patients improved with anti-PCP treatment, while one succumbed due to disease progression. Univariate analysis indicated that, compared to DIHS patients without PCP, DIHS patients with PCP received longer treatment with prednisone equivalent > 20 mg/d, had lower peripheral lymphocyte counts, CD4+ T lymphocyte counts, and albumin levels, and had a higher frequency of DIHS recurrence and CMV reactivation during the disease course （all P < 0.05）. Conclusions Cough and dyspnea are common manufestations of PCP in patients with DIHS. Prolonged use of high-dose corticosteroids, decreased peripheral lymphocytes, decreased CD4+ T lymphocytes, DIHS recurrence, CMV reactivation, and decreased albumin levels may be the influencing factors for concurrent PCP in DIHS patients.

Key words: Drug hypersensitivity syndrome, Drug eruptions, Pneumonia, Pneumocystis, Glucocorticoids, Oxazoles