Lisa Miller, aged 50 years, presents to your general practice following discharge from hospital. You had referred her to a specialist two weeks ago because of progressive shortness of breath. She advises that she was admitted to hospital by the specialist and investigated. She has been told she has interstitial lung disease but they are still awaiting results to determine the exact cause. She is worried because no one told her what this means and more importantly, she had not been given any treatment to cure the shortness of breath.
The diffuse parenchymal lung diseases (DPLDs) are a heterogeneous group of conditions associated with diffuse thickening of the alveolar walls with inflammatory cells and exudates (e.g. the acute respiratory distress syndrome-ARDS), granulomas (e.g. sarcoidosis), alveolar haemorrhage (e.g. Goodpasture's syndrome), and/or fibrosis (e.g. fibrosing alveolitis). Lung disease may occur in isolation, or as part of a systemic connective tissue disorder - for example, in rheumatoid arthritis and systemic lupus erythematosus. The DPLDs are rare and poorly understood. However, although the presentation and natural history differ, they are frequently considered collectively as they share similar symptoms, physical signs, radiological changes and disturbances of pulmonary function.
Conditions which can mimic it include:
Infection
Malignancy
Pulmonary oedema
Aspiration pneumonitis
Establishing a diagnosis is important because:
History:
Gradually progressive shortness of breath on exertion may be the only symptom, and hence the patient may not present clinically until there is extensive lung pathology. History-taking should include a thorough and comprehensive search for exposure to organic and inorganic dusts. A 'lifetime' occupational history is essential and should include hobbies that may involve similar exposures. Contact with birds at home or in the working environment is the cause of the most common form of hypersensitivity pneumonitis (HP). The smoking status should be recorded and a drug history that includes over-the-counter prescriptions should be obtained. A history of rashes, joint pains or renal disease may suggest an underlying connective tissue disorder or vasculitis. The presence of any co-morbid disease should be ascertained such as collagen vascular disease, immunodeficiency, HIV or malignancy. In exceptional cases there is a family history of DPLD.
Examination:
In many early cases, there are few, if any, physical signs. In advanced disease, tachypnoea and cyanosis may be evident at rest and there may be signs of pulmonary hypertension and right heart failure. Finger clubbing may be prominent, particularly in IPF or asbestosis. There may be restriction of lung expansion and showers of end-inspiratory crackles posteriorly and laterally. Extrapulmonary signs, including lymphadenopathy or uveitis, may be present in sarcoidosis and arthropathies or rashes may occur when a DPLD is a manifestation of a connective tissue disorder.
Investigations:
Some blood tests may be useful in indicating systemic disease or providing crude indices of disease activity (FBC, Ca²⁺, LDH, ACE, ESR, CRP). Pulmonary function tests typically show a restrictive pattern with diminished lung volumes and a reduced gas transfer, although an elevated gas transfer may be seen in cases of alveolar haemorrhage. The chest X-ray typically shows a fine reticular, reticulonodular or even nodular pattern of infiltration at the bases and periphery with cystic areas and honeycombing in advanced disease. However, plain radiography is insensitive and may not appear abnormal until disease is advanced. HRCT is more sensitive and specific and has become extremely valuable in detecting early interstitial lung disease, assessing the extent and type of involvement and guiding further investigations and management. Bronchoscopy is useful in certain circumstances. Increased numbers of lymphocytes in the bronchoalveolar lavage (BAL) may suggest either sarcoid or hypersensitivity pneumonitis, whereas a neutrophilia is more suggestive of IPF. Analysis of BAL may suggest important differential diagnoses such as infection or malignancy, and in rare instances may be diagnostic when iron-laden macrophages are seen in pulmonary haemosiderosis. Transbronchial biopsies may establish the diagnosis in sarcoidosis and in some conditions which mimic ILDs, such as lymphatic carcinomatosis and certain infections. However, it is less specific in heterogeneous disorders such as IPF where video-assisted thoracoscopy (VATS), or a limited thoracotomy, may be required to obtain a more representative sample.
Classification of Diffuse Parenchymal Lung Disease (DPLD):
Diffuse parenchymal lung disease (DPLD)
1. DPLD of unknown cause (e.g. drugs or association with collagen vascular disease)
2. Granulomatous DPLD (e.g. sarcoidosis)
3. Other forms of DPLD (e.g. lymphangioleiomyomatosis, histiocytosis X etc.)
Investigation Algorithm for Interstitial Lung Disease:
Clinical assessment including chest X-ray, pulmonary function tests, haematology, biochemical and immunological investigations
High-resolution CT
Appearances consistent with usual interstitial pneumonia
Diagnose idiopathic pulmonary fibrosis
Inconsistent clinical or CT appearances
Further investigations e.g. bronchoalveolar lavage, transbronchial biopsy, surgical biopsy
Appearances consistent with another diffuse parenchymal lung disease, e.g. sarcoid
Diagnose and treat accordingly
Sarcoidosis is a multisystem granulomatous disorder. The condition is more commonly seen in colder parts of Northern Europe where the incidence is approximately 40/10 000. The aetiology remains uncertain. Links with atypical mycobacteria and viruses remain speculative; there is some evidence of familial clustering and genetic factors are undoubtedly important. Sarcoidosis appears less commonly in smokers.
The mediastinal and superficial lymph glands, lungs, liver, spleen, skin, eyes, parotid glands and phalangeal bones are most frequently affected, but all tissues may be involved. The characteristic histological feature is a non-caseating epithelioid granuloma; fibrosis is seen in up to 20% of cases of pulmonary sarcoidosis. Disturbances in calcium metabolism reflect increased formation of calcitrol (1,25-dihydroxyvitamin D₃) by alveolar macrophages and may lead to hypercalciuria, hypercalcaemia and, rarely, nephrocalcinosis.
Typical clinical presentations:
The general practitioner plays a crucial role as an advocate and coordinator for patients who are receiving specialist care. Key responsibilities include:
Information gathering and clarification:
Strategies to support communication:
In this case, Lisa Miller should be encouraged to contact her specialist's rooms for clarification, and her GP should request a comprehensive letter outlining the diagnosis, investigation results, and management plan. The GP can then schedule a longer appointment to explain the condition, prognosis, and treatment options in detail.