Cystic fibrosis: pulmonary manifestations
Pulmonary manifestations of cystic fibrosis are some of the best known in cystic fibrosis (CF). This is partly because the lungs are often severely affected and the cause of significant morbidity and mortality.
For general discussion of cystic fibrosis, and a discussion of its other manifestations, please refer to:
- cystic fibrosis (parent article)
Clinical presentation is with the expected recurrent bacterial infections and haemoptysis. Patients have a chronic cough and expectorate copious quantities of sputum, frequently blood stained and containing mucous plugs 2,7.
Later in the disease larger volume haemoptysis, which may be life threatening, as well as pneumothoraces become more common 2.
In the lung the cystic fibrosis transmembrane regulator (CFTR) is a protein responsible for efflux of chloride and inhibition of the sodium channel's activity which controls influx of sodium. Therefore, under normal circumstances salt and chloride remain in the lumen, and keep water there osmotically. In CF patients, too little chloride is pumped out, too much sodium is reabsorbed resulting in osmotic re-absorption of water from the lumen. The result is iso-osmotic, but low volume, secretions, which tend to dry out, or be thick as they still contain all the other constituents.
Abnormal CFTR function has other effects 1,3, e.g:
- increased bacterial adhesion
- disrupted epithelial tight junctions
- altered bacterial killing
The organisms most responsible for pulmonary infections are:
- Pseudomonas aeruginosa
- Staphylococcus aureus: especially in first 6 months of life1
- Haemophilus influenzae: especially in first 6 months of life
- Burkholderia cepacia
As a result of repeated and chronic infections there is a marked increase in the number of polymorphonuclear cells (PNM) and associated inflammatory agents including elastase and collagenase. Over time these weaken the bronchial walls leading to bronchiectasis 3.
Allergic bronchopulmonary aspergillosis occurs in 5-10%
The cardinal finding of later stages of cystic fibrosis is the presence of thick walled bronchiectasis. These begin as cylindrical and progress through varicoid to cystic forms. The intervening lung is often densely fibrotic and retracted 3.
Although the entire lung is affected there is a predilection for:
- central (perihilar) distribution
- upper lobes
- apical segment of lower lobes
Other features to be sought include hyperinflation, regions of consolidation, lymph node enlargement, pneumothorax and pulmonary arterial hypertension.
Chest x-rays are insensitive to the early changes of cystic fibrosis, with changes seen on HRCT in 65% of patients with CF and normal CXR 6. Later changes include:
- lobar collapse
- pulmonary arterial enlargement due to pulmonary arterial hypertension is seen in patients with long standing disease
Disease severity can be scored on plain film using the Brasfield scoring system.
HRCT has become indispensable in the monitoring of CF patients, and is used to guide therapy and assess response to treatment, as it not only correlates with lung function tests but in some cases pre-empts them. Typically scans are repeated every 6 to 18 months depending on institution and clinical course.
Mucous plugging is of particular importance as it is thought to precede infective exacerbations and thus identification of such plugging may be used to trigger changes in therapy 4.
HRCT findings include
- bronchial wall and / or peribronchial interstitial thickening 6
- especially early in the disease
- acute infectious bronchiolitis 6
- especially early in the disease
- tree-in-bud appearance
- centrilobular nodular opacities
- branching opacities
- progresses with time from cylindrical to varicose to cystic
- signet ring sign
mosaic attenuation pattern
- due to air trapping
- best seen on expiratory scans
- mucus plugging within bronchi: finger in glove appearance
As a result of repeated examinations, patients are exposed to significant radiation dose during childhood when sensitivity to radiation is much higher. The use of low dose protocols is able to significantly reduce cumulative radiation dose 5.
Treatment and prognosis
Although there has been remarkable improvement in patient survival, respiratory failure and pulmonary complications still account for 95% of deaths in patients with cystic fibrosis 4.
Imaging differential considerations include
allergic bronchopulmonary aspergillosis (ABPA)
- may co-exist with CF in 5-10% of patients 3 ( with serum precipitins against Aspergillus fumigatus detected ~50% of patients)
- tracheobronchomegaly (Mounier-Kuhn syndrome)
- Williams-Campbell syndrome
- Langerhans cell histiocytosis (LCH)
- lymphangiomyomatosis (LAM)
- congenital cystic bronchiectasis
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- 2. Warrell DA. Oxford textbook of medicine, Sections 18-33. Oxford University Press, USA. (2005) ISBN:0198569785. Read it at Google Books - Find it at Amazon
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- 8. Vult von Steyern K, Björkman-Burtscher IM, Geijer M. Radiography, tomosynthesis, CT and MRI in the evaluation of pulmonary cystic fibrosis: an untangling review of the multitude of scoring systems. Insights Imaging. 2013;4 (6): 787-798. doi:10.1007/s13244-013-0288-y - Free text at pubmed - Pubmed citation