Interstitial pneumonia may trigger the production of anti-neutrophil cytoplasmic antibodies (ANCA) and lead to a kind of vasculitis called microscopic polyangiitis, a case report shows.
The finding suggests that interstitial pulmonary fibrosis may be a cause, rather than a consequence, of ANCA-associated vasculitis.
Interstitial lung diseases (ILD) — those that cause scarring of lung tissue — often are observed in patients with ANCA-associated vasculitis (AAV). However, studies assessing the relationship between both diseases have produced conflicting results.
While some believe ILD may be the cause of AAV, others suggest that myeloperoxidase (MPO) autoantibodies — a hallmark of AAV — cause the fibrotic tissue to proliferate.
Japanese researchers presented the case of a 72 year-old woman who developed rapidly progressing kidney inflammation (glomerulonephritis) during the course of idiopathic (unexplained) interstitial pneumonia.
Doctors first suspected interstitial pneumonia during a health checkup when she was 69. Additional analysis did not show any cause for the scarring tissue and the patient was diagnosed with idiopathic interstitial pneumonia. The patient was negative for MPO antibodies.
At age 71, the patient complained of joint pain and was suspected of having rheumatoid arthritis, after her rheumatoid factor came up elevated in blood analysis. MPO levels also were high.
While anti-inflammatory and immunosuppressive treatment reduced her symptoms, her condition continued to progress, and she was again admitted to the hospital one year later. At this point, she had swollen legs, but no other noticeable physical changes.
New blood work revealed signs of inflammation and kidney failure. Also, MPO autoantibodies were even higher than in prior analysis. An analysis of the kidneys revealed damaging glomerulonephritis, which supported a final diagnosis of microscopic polyangiitis (MPA).
Meanwhile, researchers reviewed her lung analysis and found that the pulmonary fibrosis had been progressing slowly for years.
She started treatment with methylprednisolone, followed by high-dose prednisolone and intravenous cyclophosphamide. Four months later, inflammation markers were close to normal and her kidney function had improved.
“Along with progression of idiopathic interstitial pneumonia, the test for MPO-ANCA was converted to be positive, and subsequently ANCA-associated renal vasculitis, namely MPA, developed,” the researchers wrote.
This is the tenth known case of patients who develop MPA disease after an initial idiopathic interstitial pneumonia diagnosis. The team believes that “interstitial pulmonary fibrosis may be a cause, rather than a result, of the production of ANCA, and may even be a cause of MPA.”