Pitfalls of Interstitial Lung Disease
Chinh T. Phan, DO, and Samuel Louie, MD
Phan CT, Louie S. Pitfalls of interstitial lung disease. Consultant. 2015;54(2):120-124.
Interstitial lung disease (ILD) has a history of baffling clinicians for several reasons—2 of those being confusing terminology and classification, which continue to thwart clinicians’ ability to establish a clear diagnosis. Additionally, despite promising advances in drug treatment to delay progression to fibrosis, many patients are being treated with older methods that are ineffective in improving survival, particularly for idiopathic pulmonary fibrosis (IPF).
Continued use of the term ILD can be blamed on the inflammatory changes that occur in the lung interstitium sandwiched between the alveolar epithelium and the capillary endothelium. Alveolar capillaries and peripheral small airways (traction bronchiectasis) can be involved in the disease process. Histopathological changes of “fibrosing alveolitis” cause physiological changes that can be detected by pulmonary function testing (uniformly smaller than expected lung volumes resulting in restrictive lung disease and a low carbon monoxide diffusing capacity or DLco), chest x-ray imaging, and high-resolution CT scan (HRCT) of the chest that display thickening of the lung interstitium.
It helps to remember that ILD is not actually a disease, but rather a classification of chronic pneumonias and disorders that primarily inflame and fibrose the alveolar walls. These conditions have no relationship to each other except that they can cause death from progressive pulmonary fibrosis and respiratory failure. The incentive for diagnostic evaluation always begins in the clinic office: To correctly diagnose the specific ILD present, clinicians must have a high index of suspicion, recognize risk factors, maintain contact with patients, and closely monitor changes in clinical histories over time.
The chief complaints of chronic exertional dyspnea and/or dry cough should not be ascribed to old age. Refrain from ordering tests until a complete and detailed history is taken first. A focused clinical history, which usually provides the greatest amount of information in the briefest amount of time, can help narrow the differential diagnosis and exclude asthma, chronic obstructive pulmonary disease (COPD), and cardiomyopathy. Asking about symptoms, their onset, and factors that relieve or agravate them is essential.
Physical examination of the lungs typically reveals few clues in the diagnosis of ILD. Dry crackles are best auscultated at the lungs bases just above the diaphragm posteriorly and suggest pulmonary fibrosis. On the other hand, the remainder of the examination may hint at a systemic disease linked to or associated with ILD. For example, xerostomia in Sjörgen’s syndrome, lupus pernio and erythema nodosum for sarcoidosis, malar rash in systemic lupus erythematosus, rheumatoid nodules in rheumatoid arthritis, clubbing in idiopathic pulmonary fibrosis (IPF), and lymphangitic carcinomatosis or mononeuritis multiplex in Churg-Strauss syndrome (also known as eosinophilic granulomatosis with polyangiitis or allergic granulomatosis), and abdominal pain with bloody diarrhea from inflammatory bowel disease.
Thorough documentation of occupational history, hobbies, underlying medication conditions, and drug use is also imperative in assessing the presence of ILD. HRCT chest scans and lung biopsies may also be necessary to further clarify symptoms, especially as overlapping symptoms makes early diagnoses of ILD so difficult. For example, exertional dyspnea in ILD resembles dyspnea experienced by patients with more common ailments such as asthma, COPD, and heart disease. Though ILD can be short-lived in some cases, the tendency is for it to manifest as chronic and progressive. Prognosis varies considerably depending on whether the ILD in an individual patient has a known or unknown cause or association.
CLINICAL PRESENTATION FROM PATIENT HISTORY
The classic clinical profile of an ILD patient reflects clinicians’ limited ability to suspect and diagnose ILD early. Clinicians must rely on patients and on themselves to be alert to complaints of dyspnea and/or persistent dry cough. Broad association between dyspnea and other symptoms, however, makes delayed diagnosis of ILD all too common. For example, in adult smokers between the age 40 and 70 years, initial diagnosis may be COPD based on the symptoms of cough and dyspnea on exertion. Dyspnea, though, is a very nonspecific symptom; two-thirds of cases are due to asthma, COPD, cardiomyopathy and ILD—a primary “pitfall” of ILD detection.
Patients’ nonspecific signs and symptoms must be serious enough to interfere with daily activities of living and elicit concern, but they, or their family, typically ascribe dyspnea to aging, deconditioning, and even depression. Patients must volunteer a chief complaint or the clinician must be curious enough to begin asking probing questions. A complete history often reveals a known cause for ILD or a systemic disorder associated with ILD before HRCT is done. The acronym “SOURCE”1 is a helpful tool that should be used for an efficient evaluation of ILD. (Table 1)