How does lower respiratory tract involvement manifest clinically and radiographically in Granulomatosis with polyangiitis? What is the pathology?
Clinical evidence of pulmonary disease is common on presentation (50%) in GPA, ultimately affecting 85% to 90% of patients. Approximately one-third of these patients, despite having radiographically evident pulmonary disease, do not have lower respiratory tract symptoms. Patients with relatively normal chest radiographs may have abnormal computed tomography scans showing lesions not visible on the chest x-ray. The clinical manifestations of pulmonary involvement are highly variable but can be explained by the underlying pathologic process.
Chronic inflammation results in the characteristic lesion of GPA, the granuloma, typically occurring in the extravascular interstitium of the alveolar septa, but also within vessel and airway walls. This may lead to the formation of nodules and/or fixed infiltrates on chest radiographs. The nodules may cavitate centrally. If this process is extensive, subacute or chronic respiratory insufficiency may result.
Acute inflammation results in infiltration of neutrophils and other inflammatory cells in vessel walls, extravascular interstitium, and alveolar spaces. A clinically important manifestation of acute inflammation is capillaritis, characterized by acute neutrophilic infiltration and fibrinoid necrosis within alveolar capillaries and septa, which may result in life-threatening alveolar hemorrhage.
Fibrosis may result from healing of acute or chronic inflammation. If fibrosis is diffuse, the patient may experience chronic respiratory insufficiency. Fibrosis is an uncommon manifestation of lower respiratory tract involvement.
