An earlier diagnosis of<unk>  is a prerequisite for earlier treatment and, potentially, improvement of the long-term clinical outcome of this progressive and ultimately fatal disease. If<unk>  is suspected, diagnosis can be challenging but a multidisciplinary approach involving a pulmonologist, radiologist and pathologist expert in interstitial lung disease has been shown to improve the accuracy of<unk>  diagnosis. A Multidisciplinary Consensus Statement on the<unk>  Interstitial Pneumonias published by the American Thoracic Society (ATS) and the European Respiratory Society (ERS) in 2000 proposed specific major and minor criteria for establishing the diagnosis of<unk> . However, in 2011, new simplified and updated criteria for the diagnosis and management of<unk>  were published by the ATS, ERS, together with the Japanese Respiratory Society (JRS) and Latin American Thoracic Association (ALAT). Currently, a diagnosis of<unk>  requires: * Exclusion of known causes of ILD, e.g., domestic and occupational environmental exposures, connective tissue disorders, or drug exposure/toxicity * The presence of a typical radiological pattern of usual interstitial pneumonia (UIP) on high-resolution computed tomography (HRCT). In the right clinical setting, it is possible to make the diagnosis of<unk>  by HRCT alone, obviating the need for surgical lung biopsy. Differential diagnosis Recognizing<unk>  in clinical practice can be challenging as symptoms often appear similar to those of more common diseases, such as asthma, chronic obstructive pulmonary disease (COPD) and congestive heart failure ( www.diagnoseipf.com). The key issue facing clinicians is whether the presenting history, symptoms (or signs), radiology, and pulmonary function testing are collectively in keeping with the diagnosis of<unk>  or whether the findings are due to another process. It has long been recognized that patients with ILD related to asbestos exposure, drugs (such as chemotherapeutic agents or nitrofurantoin), rheumatoid arthritis and scleroderma/systemic sclerosis may be difficult to distinguish from<unk> . Other differential diagnostic considerations include interstitial lung disease related to mixed connective tissue disease, advanced sarcoidosis, chronic hypersensitivity pneumonitis, pulmonary Langerhan's cell histiocytosis and radiation-induced lung injury. Classification Classification of IIPs.<unk>  <unk>  belongs to a large group of more than 200 lung diseases known as interstitial lung diseases (ILDs), which are characterized by the involvement of the lung interstitium, the tissue between the air sacs of the lung.<unk>  is one specific presentation of<unk>  interstitial pneumonia (IIP), which is in turn a type of ILD, also known as diffuse parenchymal lung disease (DPLD). The 2002 American Thoracic Society/European Respiratory Society (ATS/ERS) classification of IIPs was updated in 2013. In this new classification there are three main categories of<unk>  interstitial pneumonias (IIPs): major IIPs, rare IIPs, and unclassifiable IIPs. The major IIPs are grouped into chronic<unk> g IPs (this includes<unk>  and non-specific interstitial pneumonia NSIP); smoking-related IPs (i.e. respiratory bronchiolitis–interstitial lung disease RB-ILD and desquamative interstitial pneumonia DIP); and acute/subacute IPs (i.e. cryptogenic organizing pneumonia COP and acute interstitial pneumonia AIP). The diagnosis of IIPs requires exclusion of known causes of ILD. Examples of ILD of known cause include hypersensitivity pneumonitis, pulmonary Langerhan's cell histiocytosis, asbestosis, and collagen vascular disease. However, these disorders frequently affect not only the interstitium, but also the airspaces, peripheral airways, and blood vessels. Radiology Chest X-rays are useful in the follow up routine of<unk>  patients. Plain chest X-rays are unfortunately not diagnostic but may reveal decreased lung volumes, typically with prominent reticular interstitial markings near the lung bases. A chest radiograph of a patient with<unk> . Note the small lung fields and peripheral pattern of reticulonodular opacification.The radiological evaluation through HRCT is an essential point in the diagnostic pathway in<unk> . HRCT is performed using a conventional computed axial tomographic scanner without injection of contrast agents. Evaluation slices are very thin, 1–2 mm. Typical HRCT of the chest of<unk>  demonstrates fibrotic changes in both lungs, with a predilection for the bases and the periphery. According to the joint ATS/ERS/JRS/ALAT 2011 guidelines, HRCT is an essential component of the diagnostic pathway in<unk>  which can identify UIP by the presence of: * Reticular opacities, often associated with traction bronchiectasis * Honeycombing manifested as cluster cystic airspaces, typically of comparable diameters (3–10 mm) but occasionally large. Usually sub-pleural and characterized by well-defined walls and disposed in at least two lines. Generally one line of cysts is not sufficient to define honeycombing * Ground-glass opacities are common but less extensive than the reticulation * Distribution characteristically basal and peripheral though often patchy. High-resolution computed tomography scans of the chest of a patient with<unk> . The main features are of a peripheral, predominantly basal pattern of coarse reticulation with honeycombing Histology According to the updated 2011 guidelines, in the absence of a typical UIP pattern on HRCT, a surgical lung biopsy is required for confident diagnosis. Histologic specimens for the diagnosis of<unk>  must be taken at least in three different places and be large enough that the pathologist can comment on the underlying lung architecture. Small biopsies, such as those obtained via transbronchial lung biopsy (performed during bronchoscopy) are usually not sufficient for this purpose. Hence, larger biopsies obtained surgically via a thoracotomy or thoracoscopy are usually necessary. Lung tissue from people with<unk>  usually show a characteristic histopathologic UIP pattern and is therefore the pathologic counterpart of<unk> . Although a pathologic diagnosis of UIP often corresponds to a clinical diagnosis of<unk> , a UIP histologic pattern can be seen in other diseases as well, and<unk>  of known origin (rheumatic diseases for example). There are four key features of UIP including interstitial<unk>  in a 'patchwork pattern', interstitial scarring, honeycomb changes and fibroblast foci. Fibroblastic foci are dense collections of myofibroblasts and scar tissue and, together with honeycombing, are the main pathological findings that allow a diagnosis of UIP. Photomicrograph of the histopathological appearances of usual interstitial pneumonia. High-power magnification (on the right) shows a focus of fibroblastic proliferation, close to an area of<unk>  within which a mild, non-specific, chronic inflammatory cell infiltrate can be observed. In the subpleural space, a typical honeycombing aspect can be recognized. Bronchoalveolar lavage Bronchoalveolar lavage (BAL) is a well-tolerated diagnostic procedure in ILD. BAL cytology analyses (differential cell counts) should be considered in the evaluation of patients with<unk>  at the discretion of the treating physician based on availability and experience at their institution. BAL may reveal alternative specific diagnoses: malignancy, infections, eosinophilic pneumonia, histiocytosis X, or alveolar proteinosis. In the evaluation of patients with suspected<unk> , the most important application of BAL is in the exclusion of other diagnoses. Prominent lymphocytosis (>30%) generally allows excluding a diagnosis of<unk> . Pulmonary function tests Spirometry classically reveals a reduction in the vital capacity (VC) with either a proportionate reduction in airflows, or increased airflows for the observed vital capacity. The latter finding reflects the increased lung stiffness (reduced lung compliance) associated with pulmonary<unk> , which leads to increased lung elastic recoil. Measurement of static lung volumes using body plethysmography or other techniques typically reveals reduced lung volumes (restriction). This reflects the difficulty encountered in inflating the fibrotic lungs. The diffusing capacity for carbon monoxide (DLCO) is invariably reduced in<unk>  and may be the only abnormality in mild or early disease. Its impairment underlies the propensity of patients with<unk>  to exhibit oxygen desaturation with exercise which can also be evaluated using the 6-minute walk test (6MWT). Terms such as 'mild', 'moderate', and 'severe' are sometimes used for staging disease and are commonly based on resting pulmonary function test measurements. However, there is no clear consensus regarding the staging of<unk>  patients and what are the best criteria and values to use. Mild-to-moderate<unk>  has been characterized by the following functional criteria: * Forced vital capacity (FVC) of ≥50% * DLCO of ≥30% * 6MWT distance ≥150 meters.
Idiopathic pulmonary fibrosis
Sarcoidosis
Mineral dust airway disease
Hypersensitivity pneumonitis
Allergic bronchopulmonary aspergillosis
Interstitial lung disease
Rheumatoid lung disease
Idiopathic interstitial pneumonia