Anti-neutrophil cytoplasmic antibody-negative microscopic polyangiitis: A case report and literature review.

The aim of this study was to investigate the clinical characteristics, diagnosis and treatment of anti-neutrophil cytoplasmic antibody (ANCA)-negative microscopic polyangiitis (MPA). We described the case of a patient with ANCA-negative MPA and conducted analyses and a review of the relevant literature. Based on the collected data, the epidemiology, diagnosis and treatment of ANCA-negative MPA were discussed. The patient, a 69-year-old male, was initially diagnosed with pneumonia and interstitial lung disease (ILD) based on his clinical symptoms. The patient was ANCA-negative. The follow-up and consultations with the relevant departments after the ANCA testing led to a diagnosis of MPA being considered. The administration of glucocorticoids and immunosuppressant drugs was found to improve the symptoms of the patient. The clinical symptoms of MPA are unspecific. The majority of MPA cases are ANCA-positive, but misdiagnosis should be considered as a possibility in ANCA-negative cases. When patients are suspected to have MPA, therefore, ANCA tests should be immediately performed. Test results should be analyzed for the early diagnosis of MPA in order to enable the provision of immediate treatment, improve patient prognosis and reduce mortality rate.