Occupational dust exposure as a risk factor for MPO-ANCA-positive interstitial pneumonia

Background: There are recent reports that silica exposure is linked with the production of myeloperoxidase-anti-neutrophil cytoplasmic antibodies (MPO-ANCA). Purpose: To investigate the involvement and effects of dust exposure on patients with MPO-ANCA-positive interstitial pneumonia, and to elucidate the clinical differences between exposed and non-exposed groups. Subjects and Methods: The sex, age at the time of the initial diagnosis, occupational history, smoking history, initial symptoms, imaging findings, diagnosis of microscopic polyangiitis, clinical course, and cause of death were investigated in 28 patients with MPO-ANCA-positive interstitial pneumonia that presented at our hospital between 1994 and 2018. Results: Fifteen of 28 patients (54%) had a history of occupational dust exposure. The dust-exposed group (68.3 ± 8.6 years) consists of all men with a history of smoking, the majority of whom initially presented with respiratory symptoms, with 8 patients diagnosed with MPA. Thirteen patients in the non-exposed group (72.7 ±5.7 years) included five men and eight women, seven of whom were smokers. The number of patients complicated with fever and renal dysfunction in terms of initial symptoms were higher in the non-exposed group than that in the exposed group, and nine were diagnosed with MPA. The five-year survival rate was approximately 35% for both groups, and there were no significant differences. Conclusion: Approximately half of the patients with MPO-ANCA-positive interstitial pneumonia at our hospital had a history of occupational dust exposure. Patients in the exposed and non-exposed groups were characterized by different backgrounds and clinical courses.