Brief observation

Nonspecific interstitial pneumonitis as the sole histologic expression of hypersensitivity pneumonitis☆

The purpose of this analysis is to provide evidence-based and consensus-derived guidance for clinicians to improve individual diagnostic decision-making for hypersensitivity pneumonitis (HP) and decrease diagnostic practice variability.

Approved panelists developed key questions regarding the diagnosis of HP using the PICO (Population, Intervention, Comparator, Outcome) format. MEDLINE (via PubMed) and the Cochrane Library were systematically searched for relevant literature, which was supplemented by manual searches. References were screened for inclusion, and vetted evaluation tools were used to assess the quality of included studies, to extract data, and to grade the level of evidence supporting each recommendation or statement. The quality of the evidence was assessed using the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) approach. Graded recommendations and ungraded consensus-based statements were drafted and voted on using a modified Delphi technique to achieve consensus. A diagnostic algorithm is provided, using supporting data from the recommendations where possible, along with expert consensus to help physicians gauge the probability of HP.

The systematic review of the literature based on 14 PICO questions resulted in 14 key action statements: 12 evidence-based, graded recommendations and 2 ungraded consensus-based statements. All evidence was of very low quality.

Diagnosis of HP should employ a patient-centered approach and include a multidisciplinary assessment that incorporates the environmental and occupational exposure history and CT pattern to establish diagnostic confidence prior to considering BAL and/or lung biopsy. Criteria are presented to facilitate diagnosis of HP. Additional research is needed on the performance characteristics and generalizability of exposure assessment tools and traditional and new diagnostic tests in modifying clinical decision-making for HP, particularly among those with a provisional diagnosis.

Uncommon forms of idiopathic interstitial pneumonia include idiopathic nonspecific interstitial pneumonia, acute interstitial pneumonia, lymphoid interstitial pneumonia, and idiopathic pleuroparenchymal fibroelastosis, with many additional patients having unclassifiable interstitial lung disease. In this chapter, we provide an overview of the clinical, radiologic, and pathologic features of these disorders as well as a brief discussion about clinical course, management, and prognosis of each entity.

Exposure related interstitial lung diseases (ILD) are often underrecognized as they require consideration of exposure in the differential diagnosis of disease. Although pneumoconioses including asbestosis, coal worker’s pneumoconiosis and silicosis are most frequently cited, other exposure related ILDs continue to be identified. The clinico-radiographic-pathologic patterns seen in idiopathic interstitial pneumonias, where causation is supposedly unknown, have been associated with specific exposures. Identifying relevant exposures to identify pneumoconioses and similar diseases, require a comprehensive exposure history. When trying to establish new disease exposure relationships, collaboration between clinicians, the workplace, local health departments, and occupational health agencies can be critical. Respiratory surveillance programs along with personal protection equipment, including respirators, and local engineering controls are key to primary and secondary prevention programs.

Interstitial lung diseases encompass a broad range of numerous individual conditions, some of them characterized histologically by fibrosis, especially idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, chronic hypersensitivity pneumonia, interstitial lung disease associated with connective tissue diseases, and unclassifiable interstitial lung disease. The diagnostic approach relies mainly on the clinical evaluation, especially assessment of the patient's demographics, history, smoking habits, occupational or domestic exposures, use of drugs, and on interpretation of high-quality HRCT of the chest. Imaging is key to the initial diagnostic approach, and often can confirm a definite diagnosis, particularly a diagnosis of idiopathic pulmonary fibrosis when showing a pattern of usual interstitial pneumonia in the appropriate context. In other cases, chest HRCT may orientate toward an alternative diagnosis and appropriate investigations to confirm the suspected diagnosis. Autoimmune serology helps diagnosing connective disease. Indications for bronchoalveolar lavage and for lung biopsy progressively become more restrictive, with better considerations for their discriminate value, of the potential risk associated with the procedure, and of the anticipated impact on management. Innovative techniques and genetics are beginning to contribute to diagnosing interstitial lung disease and to be implemented routinely in the clinic. Multidisciplinary discussion, enabling interaction between pulmonologists, chest radiologists, pathologists and often other healthcare providers, allows integration of all information available. It increases the accuracy of diagnosis and prognosis prediction, proposes a first-choice diagnosis, may suggest additional investigations, and often informs the management. The concept of working diagnosis, which can be revised upon additional information being made available especially longitudinal disease behaviour, helps dealing with diagnostic uncertainty inherent to interstitial lung diseases and facilitates management decisions. Above all, the clinical approach and how thoroughly the patient's history and possible exposures are assessed determine the possibility of an accurate diagnosis.

This chapter is devoted to the description of morphological, clinical, and radiological features of idiopathic interstitial pneumonia (IIP). The main diagnostic features of IIP are defined, and each clinical type is described with a wide range of high-resolution computed tomography series, allowing visual comparison of closely related radiological patterns. For most common forms, descriptions of the alveoloscopic picture are provided. Differential diagnosis of IIP is often challenging, so key diagnostic points for similar diseases are discussed. Modern approaches for management of patients with IIP are also considered.

Nonspecific interstitial pneumonia (NSIP) is a form of chronic interstitial pneumonia that should be separated from the other idiopathic interstitial pneumonias, including most importantly, usual interstitial pneumonia (UIP). Diagnosis is predicated on identification of characteristic findings in a surgical lung biopsy in the appropriate clinical and radiological context. Affected patients may have a variety of underlying or associated conditions, although most have a form of idiopathic lung disease associated with a more favorable prognosis than UIP/idiopathic pulmonary fibrosis (IPF). Keys to distinguishing NSIP from UIP include absence of heterogeneous lung involvement, architectural distortion in the form of fibrotic scarring and/or honeycomb change, and fibroblast foci in NSIP.