Interstitial lung diseases (ILDs) or diffuse parenchymal lung diseases are terms used to describe around 200 acute and chronic lung disorders (Raghu and Brown, 2004). They are a heterogeneous group of disorders of the lower respiratory tract that are characterised by both acute and chronic inflammation and a generally irreversible and relentless process of fibrosis in the interstitium and the alveolar walls (air sacs in the lungs) (Riches et al, 2003).
The term ILD is misleading, as the interstitium refers to the region of the alveolar wall that separates the alveolar epithelial cells and the capillary endothelial cells where the exchange of oxygen and carbon dioxide takes place (Turner-Warwick, 1990). ILDs, on the other hand, affect all components of the alveolar wall, the fibrotic process extending beyond the interstitium into the alveolar space, the acini, the bronchiolar lumen and the bronchioles (Raghu and Brown, 2004).
ILDs can be classified broadly into the following categories:
- Those with a known cause, such as occupational/environmental factors, drugs and infections;
- Those associated with systemic disorders, such as sarcoidosis or connective tissue diseases; for example, scleroderma or rheumatoid arthritis;
- Rare miscellaneous conditions, such as the idiopathic interstitial pneumonias (Green and Johnston, 2002).
The cause of an ILD is usually unknown. Schwarz et al (2003), suggest that some form of injury to the alveolar epithelial cells initiates the pathogenic process and that this results in an inflammatory response and fibrosis of the lung. Continuous inflammatory events ultimately lead to the collapse and fusion of the alveoli and to fibrosis, which results in a loss of surface area in the lung where gaseous exchange can take place (Riches et al, 2003).
Until recently, the use of different terminology to describe ILDs and the lack of standard diagnostic criteria prevented the development of a logical approach to the assessment and management of these diseases (American Thoracic Society (ATS), European Respiratory Society (ERS), 2002). As a large number of disorders are included under the term ILD, Wells (2002) suggests subdividing them into categories commonly encountered in clinical practice. Because there are differences in the treatment and prognosis of different types of the disease, an accurate diagnosis is essential to ensure appropriate management (Fig 1).
Interstitial lung diseases have certain clinical and pathologic features in common. The onset of symptoms is usually gradual, with breathlessness the most common and disabling symptom (Turner-Warwick, 1980). A non-productive cough is usual and may be paroxysmal (sudden and spasmodic) (American Thoracic Society, 2000).
Abnormal breath sounds are present on auscultation; fine crackles are most prominent at the lung bases and are heard during mid-to late inspiration. Digital clubbing is seen in 70 per cent of patients and the clinician should look for signs of scleroderma (thickening of the skin that may be associated with a multisystem disorder) and other systemic diseases (du Bois and Wells, 2001).
There will be abnormal findings on chest X-ray or on a high-resolution computerised tomography scan. Lung function tests will show a restrictive pulmonary physiology (Johnston et al, 1997) (Table 1). Lung function tests will include measuring the following:
- Forced expiratory volume in one second (FEV1). This measures the amount of air that can be exhaled as a forced blow in one second from maximum inhalation;
- Forced vital capacity (FVC). This is the total volume of air that can be exhaled with maximum force, starting from maximum inhalation to maximum exhalation.
Patients with ILD will have a restrictive pattern, with a reduced FEV1 and FVC.
Presentation of the disease
An ILD affects each person differently and progresses at varying rates. Generally, the patient’s breathlessness becomes worse over time, making daily activities of living such as walking, washing and dressing more difficult. A reduction in oxygen concentration in the arterial blood supply (hypoxaemia) may develop. Pulmonary hypertension is a characteristic of the latter stages of the disease and an important indicator of prognosis (Conron and du Bois, 1999).
As the disease progresses, the patient may require supplementary oxygen (Lindell and Jacobs, 2003).
A thorough physical examination and detailed history are vital to achieving an accurate diagnosis. These should include a full history of possible exposure to occupational or environmental causes of the disease; for example, asbestos.
The assessment should also explore co-existing or past systemic disease and drug therapy, so as to exclude an ILD caused by drugs such as cytotoxic agents. Family and smoking history, and the possibility of underlying immunosuppression for example, immunosuppression associated with HIV (American Thoracic Society and the European Respiratory Society, 2002), should also be assessed. Table 1 describes the tests that can assist with an accurate diagnosis.
Currently, there is no cure for ILDs, but a variety of drugs is available and the aim of treatment is to inhibit inflammation and subsequent fibrosis. Treatment also helps to distinguish between reversible disease, where the patient’s condition improves, and irreversible fibrotic disease, when the goal is to prevent its progression (Wells, 2002).
Treatment options are similar for the various types of an ILD, but some drugs may be more efficacious for one disease than another (Baughman et al, 2004). Treatment regimens include, corticosteroids (prednisolone) and corticosteroids combined with immunosuppressive therapy, most commonly cyclophosphamide or azathioprine. Prednisolone is used to reduce inflammation and azathioprine and cyclophosphamide to suppress the body’s immune response.
Response to treatment/survival - Idiopathic pulmonary fibrosis (IPF) responds poorly, if at all, to treatment (Collard and King, 2004). Patients with this disease should be referred as soon as possible for lung transplantation, as it has been shown to prolong survival (American Thoracic Society and the European Respiratory Society, 2002). Other types of ILDs have been shown to respond better to treatment and the chances of survival are greater (Collard and King, 2004).
Experimental treatment and research - Recent advances in understanding the causes of ILDs are leading to targeted interventions that may influence survival and quality of life. The following drug therapies are currently under investigation in clinical trials:
- Anti-fibrotics (interferon gamma and bosentan);
- Anti-inflammatory drugs with antifibrotic effect (etanercept, a tumour necrosis factor alpha inhibitor);
- Anti-oxidants (N-acetylcysteine).
A number of antifibrotic agents that interfere with collagen synthesis have been tested in clinical trials - pirfenidone, colchicine and penicillamine - but they have not had any effect on mortality (Lasky and Ortiz, 2001).
Lung transplantation - Unless there are contraindications, lung transplantation should be considered for patients with an ILD who have severe functional impairment, oxygen dependency and whose condition is deteriorating. Single lung transplantation for end-stage idiopathic pulmonary fibrosis has been successful, and the survival rates of 60 per cent at three years are encouraging (Mogulkoc et al, 2001). Double-lung transplantation is preferred for patients with pulmonary hypertension (Lindell and Jacobs, 2003).
In end-stage disease, supportive therapy is crucial to minimising morbidity. Supplemental oxygen may help to alleviate the dyspnoea of respiratory failure and improve the function of other organs. Palliative care should be offered even though the patient is having treatments to slow or stabilise the disease. Nurses should help the patient gain access to palliative care and decide whether and when to begin hospice care (Lindell and Jacobs, 2003).
Caring for patients with an interstitial lung disease is a major challenge to the nurse, as the course of the disease can be uncertain and it is often the nurse who provides support, education and counselling. Patients require information about patho-physiology, the progression of the disease, treatment, and an explanation of any diagnostic procedures.
The experience of breathlessness can have a profound impact on quality of life, affecting almost every activity of daily living and requires a multidisciplinary, patient-centred approach (Stent, 2001). Teaching effective breathing patterns can reduce the fear of dyspnoea, reduce the work of breathing and promote adequate gas exchange for normal daily activities (Lynes and Kelly, 2003).
People who are told they have developed a chronic respiratory condition may need to make a number of behavioural, social and psychological adjustments. Inevitably, the impact of diagnosis changes the way patients view themselves, their lives and the future (Lynes and Kelly, 2003).
Studies in primary care have shown that improvements for patients with respiratory disease can be achieved by adhering to clinical guidelines and providing specialist training for health care professionals (Fletcher, 2004).