Introduction Primary pneumothorax has been defined as occurring in patients with no known lung disease but the assumption that the underlying lung is normal is increasingly contentious. The purpose of this case-control study is to evaluate lung structure and quantify the extent of any emphysema in patients with primary and secondary spontaneous pneumothorax compared with a control group without pneumothorax and to assess the influence of smoking on this process
Methods 20 patients with primary pneumothorax (PSP), 20 patients with secondary pneumothorax (SSP) and 40 control patients with computed tomography scans suitable for quantitative analysis were evaluated. Demographics and smoking histories were collated. Quantitative evaluation of low attenuation areas of the lung was performed using semi-automated software. The percentage of segmented lung below the low attenuation threshold value of -950 Hounsfield units was calculated, based on a previously validated threshold.1 The extent of emphysema-like destruction was also assessed visually by an experienced consultant chest radiologist.
Results The extent of emphysema and percentage low attenuation area was greater in PSP patients compared with controls matched for age and smoking history (Median 0.25 vs 0.00, p = 0.019) and was also higher in SSP compared with PSP patients (16.15 vs 0.25, p < 0.001). PSP patients who smoked had significantly greater low attenuation area than PSP non-smokers (0.7 vs 0.1, p = 0.034). No such difference was detected between smokers and non-smokers within the control group (0.0 vs 0.05, p = 0.798).
Conclusions The majority of patients with PSP had quantifiable evidence of parenchymal destruction and emphysema. The presented data is supportive of the hypothesis that there is likely to be a spectrum of lung damage ranging from ‘normal patients’ through to patients with SSP, and rather than a clear distinction between PSP and SSP these conditions exist on a continuum.
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