Interstitial Lung Disease (ILD) - also known as diffuse parenchymal lung disease (DPLD) - refers to a group of complex, heterogenous pulmonary disorders that collectively account for 15% of all lung disease.
ILD primarily affects the:
ILD is characterized by:
Due to the multifactorial pathogenesis of the 150 different subtypes of ILD, classification is often difficult and no consensus has been reached as yet.
Generally, the most simplified method of approaching ILD is to stratify its subtypes into:
In clinical practice, some forms of ILD are more frequently encountered than others. Hence, it is important to be aware of the following more common types of ILD and consider them in your differential diagnosis of a patient with deteriorating lung function and a restrictive ventilatory defect.
Recent research studies have found that many drugs commonly used in hospital and primary care environments also have a hand in the pathogenesis of ILD. Hence, reviewing a patient's medication history is an important step in the assessment of a patient with deteriorating lung function and no obvious underlying cause.
When the patient presents in clinic:
A patient with ILD might present with a history of:
Other possible signs and symptoms:
Additional questions you may ask:
NB: note the absence of wheeze or other evidence of airway obstruction to confirm restrictive pathology.
Look out for:
Findings from a CXR of a patient with IPF:
Routine baseline investigations for most patients with suspected ILD:
Additional tests to be performed at the clinician's discretion:
For some patients, a general diagnosis of ILD may be reached by this point. However, more information may be needed to reach a final diagnosis of the subtype of ILD involved, especially for the Idiopathic Interstitial Pneumonias, which are diagnosed primarily on their appearance on HRCT in combination with cytological and histological findings.
ILD is usually managed according to a patient's underlying condition. In some cases, no intervention is necessary. For example, due to the high rates of spontaneous remission with mild asymptomatic lung involvement in sarcoidosis, treatment is not recommended.
For idiopathic ILD, treatment regimens are mainly aimed at slowing the progression of the disease, as curative treatment of IIPs remains elusive. Generally, a patient will continue to experience declining lung function due to the limitations of his medical management - in some severe cases, a lung transplantation may be an option to consider.
This section will discuss the medical management of a patient with IPF, as relevant to our case.
Initiating the treatment of IPF
Treatment can be initiated at presentation, or with disease progression, or alternatively only begin when the patient demonstrates moderate disease. Although this decision is up to the clinician's discretion, more doctors are beginning to treat patients upon presentation in the hopes of an improved clinical course and delayed progression to severe, debilitating respiratory limitation.
Immunosuppressive therapy in IPF
Although the pathogenesis of IPF is still debatable, it is commonly believed that these unexplained fibrotic parenchymal changes are secondary to the dysfunction of immunoregulatory pathways in the lung. Hence, immunosuppressive therapy - prednisolone, azathioprine and N-acetylcysteine (NAC) - is often employed as the long-term treatment regimen in a patient with IPF.
For patients with poor tolerance of azathioprine, methotrexate and ciclosporin are possible alternatives. However, the use of methotrexate remains controversial due to its paradoxical worsening of lung fibrosis in certain patients. As a result, patients being treated with methotrexate require constant monitoring of their lung function to assess their disease states.
Best supportive care
As IPF remains a progressive, incurable disease, it is important to have a multifaceted, proactive approach to symptomatic treatment. This involves:
Additional recommendations for IPF:
1. Why is it relevant that the patient contracted pneumonia?
Pneumonia is one of the leading causes of death in the elderly, who are generally prone to infections in the urinary tract, skin, and chest. This, compounded with the fact that he was a patient with underlying IPF and COPD, presented quite a worrying clinical picture. Due to his decreased ventilatory efficiency and history of immunosuppressive therapy with azathioprine, he was extremely susceptible to rapid clinical deterioration.
2. How do we know that he had pneumonia?
Although it is true that the patient did not mention any of the textbook signs suggesting pneumonia, the fact that he had underlying IPF and purulent sputum raised a high index of suspicion that he might have had a chest infection. Our patient suffered from generalized weakness, myalgia, and arthralgia which ultimately caused his repeated falls - these signs were all suggestive of an infection due to their short clinical course. As the patient had a longstanding history of IPF, it was important to consider whether he had begun to normalize any deterioration in lung function and attribute it to his condition without consulting his GP. Hence, his account of his respiratory symptoms only became comprehensive after repeated prompting, whereby it was revealed that his exercise tolerance had become severely hampered, as while he was normally able to walk about 10 yards before resting, he was now severely dyspnoeic at rest. Ultimately, the diagnosis of pneumonia was confirmed by a chest X-ray after other causes for his recurring falls were ruled out.
3. Why did the patient have coarse crackles on auscultation instead of the fine end-inspiratory crackles that one would expect in IPF?
Areas of fibrosis are often more prone to infection, due to the impaired function of the parenchyma in that region to clear any bacteria and residual cell debris. As a result, auscultation revealed that the infection had settled in the fibrotic regions of his lung - as coarse crackles are a sign of infection, they had been superimposed on the fine end-inspiratory crackles you would ordinarily expect to find on a patient with IPF and were thus recorded as the primary finding on auscultation in the respiratory examination.
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