Comorbidity of autoimmune diseases in patients with autoimmune pulmonary alveolar proteinosis

Autoimmune diseases coexisting with autoimmune pulmonary alveolar proteinosis (APAP) are rare. Therefore, the clinical characteristics of complications of these diseases are not well known.

We examined clinical data of APAP patients with autoimmune diseases as a retrospective study in a single center.

Among 100 APAP patients, ten (10.0%) had autoimmune diseases including rheumatoid arthritis (n = 3), polymyalgia rheumatica (n = 1), adult-onset Still's disease (n = 1), polymyositis (n = 1), immune thrombocytopenia (n = 1), autoimmune hepatitis (n = 1), dermatomyositis (n = 1), and psoriasis vulgaris (n = 1). Autoimmune diseases preceded the onset of APAP in nine patients (90.0%). At the onset of APAP, pulmonary lesions were diagnosed with interstitial lung disease (n = 8), secondary pulmonary alveolar proteinosis (n = 1), and pneumocystis pneumonia (n = 1). Compared with APAP patients without autoimmune diseases (n = 90), patients with autoimmune diseases (n = 10) were predominantly female (80.0 vs. 37.8%, P = 0.021) and significantly older at the time of diagnosis of APAP (mean 65.8 vs. 54.0 years old, P < 0.001). Eight patients (80.0%) had received immunosuppressive therapy when they were diagnosed with APAP. The chest CT findings of APAP improved after withdrawal of prednisolone in two patients. During the observation periods, one patient died (10.0%) and pulmonary fibrosis developed in three patients (30.0%).

In patients with autoimmune diseases, APAP at its onset can be misdiagnosed as other pulmonary diseases, specifically interstitial lung disease. The use of immunosuppressive drugs may be associated with worsening APAP.