Histopathological approach to patterns of interstitial pneumonia in patient with connective tissue disorders

It is well established that some patients with connective tissue disorders will suffer from pulmonary disease at some stage in their disease progression. This article concentrates on the interstitial pneumonias, seen in association with most types of connective tissue disorder, particularly in the ligh of non-specific interstitial pneumonia (NSIP) being recognised as a distinct histological pattern. Most published articles on this subject precede recognition of NSIP and, as such, the relative incidence of patterns of interstitial pneumonia, as defined by the International Consensus Classification Committee for Interstitial Lung Disease (ICCILD), as well as the clinical and prognostic significance of these patterns is undergoing further scrutiny. In this review, the recognised histological patterns, namely usual interstitial pneumonia (UIP), non-specific interstitial pneumonia (NSIP), diffuse alveolar damage (DAD), organising pneumonia (OP), reactive pulmonary lymphoid hyperplasia, desquamative interstitial pneumonia (DIP) and respiratory bronchiolitis-associated interstitial lung disease (RBILD) are reviewed systematically in relation to the various subgroups of connective tissue disorders. As yet, there are few published studies, but current evidence suggests that many cases previously classified as fibrosing alveolitis are likely to show a pattern of NSIP rather than UIP, particularly in relation to systemic sclerosis. The histological pattern of usual interstitial pneumonia, the most frequently seen pattern in biopsies from patients with idiopathic pulmonary fibrosis/cryptogenic fibrosing alveolitis, appears to be comparatively rare. Furthermore, any biopsy showing a combination of histological patterns, a pattern of non-specific interstitial pneumonia or a pattern of lymphoid interstitial pneumonia/follicular bronchiolitis should be thoroughly investigated for a background connective tissue disorder, if previously unsuspected. Finally, the recently published prognostic data relating to these histological patterns in idiopathic disease should not be extrapolated to patients with connective tissue disorders.