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Interstitial lung diseases comprise a group of disorders that have the common features of inflammation (pneumonitis) and fibrosis of the interalveolar septum, representing a non-specific reaction of the lung to injury of various causes.8,9
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In many there is a hypersensitivity reaction to various unusual antigens. The fibrosis may be localised as following unresolved pneumonia, bilateral as with tuberculosis or widespread.
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Consider the possibility of fibrosis of the lungs in chronic dyspnoea and a dry cough with normal resonance.
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Causes of widespread interstitial pulmonary fibrosis include:
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idiopathic pulmonary fibrosis
hypersensitivity pneumonitis (extrinsic allergic alveolitis)
drug-induced
lymphangitis carcinomatosis
various occupational lung disorders
rheumatoid arthritis
sarcoidosis
acute pulmonary oedema
immunological/multisystemic disease (e.g. connective tissue disorders, RA, vasculitis, inflammatory bowel disease)
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Common clinical features:
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dyspnoea and dry cough (insidious onset)
fine inspiratory crackles at lung base with faint breath sounds
cyanosis and finger clubbing may be present
PFTs:
characteristic X-ray changes
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High-resolution CT scanning has been a major advance in diagnosis. May show ‘honeycomb lung’.
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Idiopathic pulmonary fibrosis
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Idiopathic pulmonary fibrosis, also known as idiopathic fibrosing interstitial pneumonia and cryptogenic fibrosing alveolitis, is the most common diagnosis among patients presenting with interstitial lung disease.
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Patients usually present in the fifth to seventh decade with the clinical features as outlined under interstitial lung diseases such as slowly progressive dyspnoea over months to years. Chest X-ray abnormalities are variable but include bilateral diffuse nodular or reticulonodular shadowing favouring the lung bases. High-resolution CT scans are effective for diagnosis. Open lung biopsy may be needed for diagnosis and staging. The usual prognosis is poor, with death occurring about 3.5–5 years after diagnosis. The usual treatment is high doses of oral corticosteroids with azathioprine and no smoking.9,10
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If refractory, refer to a palliative care service.11
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Pulmonary sarcoidosis
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Sarcoidosis is a multisystemic disorder of unknown aetiology, which is characterised by non-caseating granulomatous inflammation that involves the lung in about 90% of affected patients. A characteristic feature is bilateral hilar lymphadenopathy, which is often symptomless and detected on routine chest X-ray (CXR). Radiological lung involvement can be associated with or occur independently of hilar lymphadenopathy.
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May be asymptomatic (one-third)
Onset usually third or fourth decade (but any age)
Bilateral hilar lymphadenopathy (on CXR)
Cough
Fever, malaise, arthralgia
Skin lesions: erythema nodosum, lupus pernio
Ocular lesions (e.g. anterior uveitis)
Other multiple organ lesions (uncommon)
Overall mortality 2–5%
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Erythema nodosum with an acute swinging fever, malaise and arthralgia in a young adult female is diagnostic of sarcoidosis.
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Histological evidence from biopsy specimen, usually transbronchial biopsy (essential if an alternative diagnosis, e.g. lymphoma, cannot be excluded) or skin biopsy in cases of erythema nodosum. A better modern diagnostic method is biopsy via video-assisted thoracoscopy.
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elevated serum ACE (non-specific)
PFTs: restrictive pattern; impaired gas transfer in advanced cases
±ve Kveim test (not recommended these days)
serum calcium
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Sarcoidosis may resolve spontaneously (hilar lymphadenopathy without lung involvement does not require treatment).
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Indications for treatment with corticosteroids:
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no spontaneous improvement or worsening after 3–6 months
symptomatic pulmonary lesions
eye, CNS and other systems involvement
hypercalcaemia, hypercalciuria
erythema nodosum with arthralgia
persistent cough
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Corticosteroid treatment9
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Prednisolone 0.5 mg/kg (up to 50 mg) (o) daily for 4–6 weeks, then reduce to lowest dose that maintains improvement.9 If there is a response, taper the dose to 10–15 mg (o) daily as a maintenance dose for 6–12 months.9
Prednisolone 20–30 mg for 2 weeks for erythema nodosum of sarcoidosis.
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Glossary of terms
Chronic airflow limitation A physiological process measured as impairment of forced expiratory flow, which is the major cause of dyspnoea in these patients.
Chronic bronchitis A clinical condition characterised by a productive cough on most days for at least 3 months of the year for at least 2 consecutive years in the absence of any other respiratory disease that could be responsible for such excessive sputum production (such as tuberculosis or bronchiectasis).
COPD A chronic, slowly progressive disorder characterised by the presence of airway obstruction, which may (or may not) be partially reversible by bronchodilator therapy.8
Emphysema This is defined in pathological rather than clinical terms, as permanent dilatation and destruction of lung tissue distal to the terminal bronchioles.
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Hypersensitivity pneumonitis
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Hypersensitivity pneumonitis (extrinsic allergic alveolitis) is characterised by a widespread diffuse inflammatory reaction in both the small airways of the lung and the alveoli, due to the inhalation of allergens, which are usually spores of micro-organisms such as thermophilic actinomycetes in ‘farmer’s lung’ or (more commonly) avian protein from droppings or feathers in ‘bird fancier’s lung’. Occupational causes of extrinsic alveolitis have been described by Molina12 (see TABLE 49.7).
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Illness may present as acute or subacute episodes of pyrexia, chills and malaise with dyspnoea and a peripheral neutrophil several hours after exposure.12 Management is based on prevention, namely avoiding exposure to allergens or wearing protective, fine-mesh masks. Prednisolone can be used (with caution) to control acute symptoms. It should be pointed out that this allergic disorder is different from the infection psittacosis.
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Drug-induced interstitial lung disease9
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Drugs are an important cause of this disorder and have three main effects:
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Alveolitis with or without pulmonary fibrosis. This is mainly due to cytotoxic drugs, nitrofurantoin and amiodarone. The drug should be removed and consideration given to prescribing prednisolone 50 mg (o) daily for several weeks, depending on response.
Eosinophilic reactions. This is presumably an immunological reaction, which may present as wheezing, dyspnoea, a maculopapular rash and pyrexia. The many implicated drugs include various antibiotics, NSAIDs, cytotoxic agents, major tranquillisers and antidepressants, and anti-epileptics. Treatment is drug removal and a short course of prednisolone 20–40 mg (o) daily for 2 weeks.
Non-cardiogenic acute pulmonary oedema. This is rare and has been reported to occur with opioids, aspirin, hydrochlorothiazide, β2-adrenoceptor agonists (given IV to suppress premature labour), cytotoxics, interleukin-2, heroin.
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OCCUPATIONAL PULMONARY DISEASE
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Various types of acute and chronic pulmonary diseases are related to exposure to noxious substances such as dusts, gases and vapours in the workplace. Common chemical causes include formaldehyde used in processed woods, e.g. chipboard and medium-density fibre. GPs have a crucial role in the identification of the possible work-relatedness of lung disease.
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Disorders due to chemical agents include:
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obstructive airways disorders, such as occupational asthma, acute bronchitis, (chronic) industrial bronchitis, byssinosis (asthma-like condition due to cotton dust)
hypersensitivity pneumonitis
pulmonary fibrosis (pneumoconiosis) due to mineral dust
lung cancer due to industrial agents such as asbestos, various hydrocarbons
pleural disorders, usually associated with asbestosis
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The term ‘pneumoconiosis’ refers to the accumulation of dust in the lungs and the reaction of tissue to its presence, namely chronic fibrosis. The main cause worldwide is inhalation of coal dust, a specific severe variety being progressive massive fibrosis (complicated coal worker’s pneumoconiosis) in which the patient suffers severe dyspnoea of effort and a cough often productive of black sputum. TABLE 49.8 summarises the important causes.
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Of particular concern are diseases caused by inhalation of fibres of asbestos, which is a mixture of silicates of iron, magnesium, cadmium, nickel and aluminium. These diseases include asbestosis, diffuse pleural thickening, pleural plaques, mesothelioma and increased bronchial carcinoma in smokers. Pulmonary asbestosis has classic X-ray changes but high-resolution CT scans may be required to confirm the presence of calcified pleural plaques. It usually takes 10–20 years from exposure for asbestosis to develop and 20–40 years for mesothelioma to develop,8 while bronchial carcinoma is caused by the synergistic effects of asbestosis and cigarette smoking.
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Acute respiratory distress syndrome (ARDS)
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ARDS, also known as acute lung injury and formerly called ‘adult respiratory distress syndrome’, refers to acute hypoxaemic respiratory failure following a pulmonary or systemic insult with no apparent cardiogenic cause of pulmonary oedema. This occurs about 12–48 hours after the event.13 The most common cause is sepsis, which accounts for about one-third of ARDS patients. The mortality rate is 30–40%, increasing if accompanied by sepsis. Management is based on early diagnosis, early referral, identification and treatment of the underlying condition and then optimal intensive care.14
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Sudden onset of respiratory distress
Stiff lungs—reduced lung compliance
Refractory hypoxaemia
Bilateral pulmonary infiltrates on X-ray
No apparent evidence of congestive heart failure
Absence of elevated left atrial pressure
Specific gas exchange abnormalities
Signs: tachypnoea, laboured breathing, rib retraction, central cyanosis, fine crackles on auscultation
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The differential diagnoses are pneumonia and acute heart failure. Common risk factors/associations for ARDS include (indirectly—systemic)—sepsis, shock, trauma, burns, drug overdose (e.g. heroin), multiple transfusions, obstetric complications (e.g. eclampsia, amniotic fluid embolism), and many direct causes such as pulmonary aspiration, toxic gas inhalation, blast injury and pneumonia (e.g. SARS). Admit patient to an intensive care unit.
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Severe acute respiratory syndrome (SARS)7
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SARS is a respiratory illness of varying severity (mild to severe) with a known mortality rate of about 10% of clinically established cases. All cases to date exhibit a high fever of >38°C. It is considered to be an atypical pneumonia caused by a quite unique coronavirus (SARS–CoV). Cases have acquired SARS following exposure to endemic areas of South-East Asia. Severe cases (up to 10% mortality) can progress to ARDS.
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Suspected case = fever >38°C + cough, breathing difficulty or dyspnoea + contact with SARS person/area. Plain X-rays may show pulmonary infiltrates while high-resolution CT scans may show typical patterns.
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Symptoms of atypical pneumonia: fever, cough, dyspnoea
Associated may be myalgia, diarrhoea, headache, sore throat, rhinorrhoea, confusion, malaise, rash
Virulent virus—droplet spread by close contact
Incubation period 2–7 days
Crackles and wheezes may be present on auscultation but no hallmark sign
Non-specific X-ray signs
Prime CT scans may show typical changes
Diagnosis confirmed by PCR studies or isolation of the virus on culture
Complications appear to be confined to the lung
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Optimal treatment for SARS by drugs is still being evaluated. Management is supportive; supplemental oxygen is required. Preventive measures, including wearing of face masks (NIOSH standard mask best) and appropriate infection control procedures, are important. Wear a mask, gloves, goggles and gown for clinical assessment of suspected cases and switch off air-conditioning (refer to CHAPTER 28).
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Practice tips
Remember to order a chest X-ray and pulmonary function tests in all doubtful cases of dyspnoea.
All heart diseases have dyspnoea as a common early symptom.
Increasing dyspnoea on exertion may be the earliest symptom of incipient heart failure.
Several drugs can produce a wide variety of respiratory disorders, particularly pulmonary fibrosis and pulmonary eosinophilia. Amiodarone and cytotoxic drugs, especially bleomycin, are the main causes.
Dyspnoea in the presence of lung cancer may be caused by many factors, such as pleural effusion, lobar collapse, upper airway obstruction and lymphangitis carcinomatosis.
The abrupt onset of severe dyspnoea suggests pneumothorax or pulmonary embolism.
If a patient develops a relapse of dyspnoea while on digoxin therapy, consider the real possibility of digoxin toxicity and/or electrolyte abnormalities leading to left heart failure.
Recurrent attacks of sudden dyspnoea, especially waking the patient at night, are suggestive of asthma or left heart failure.
Causes of hyperventilation include drugs, asthma, thyrotoxicosis and panic attacks/anxiety.