Spontaneous Pneumothorax : some epidemiological aspects
Pneumothorax refers to the entry of air into the pleural space. More than half of the pneumothoraces are traumatic (accidental or iatrogenic); the remaining occur without any preceding trauma and are labelled spontaneous. latrogenic pneumothorax is a fairly well recognised complication associated with several invasive procedures such as: trans-bronchial lung biopsies, per-cutaneous needle biopsies, central venous lines, etc. Positive pressure ventilation in the intensive care set-up has a special risk for causing pneumothorax and pneumomediastinum.
Spontaneous pneumothorax (SP) is an important medical problem affecting mainly young individuals. SP can be divided into two types:
Secondary Spontaneous Pneumothorax (SSP) is defined when as underlying disease state responsible for causing pneumothorax can be identified.
Primary Spontaneous Pneumothorax (PSP) is the 'idiopathic' variety, which occurs in an otherwise healthy person.
Several studies have shown PSP to be more common among young men, who are tall, thin and smokers. Certain epidemiological facts about the SP are outlined below:
Incidence: There are remarkably few studies in this area. In a large study from Minnesota, USA, the incidence of PSP among men was 7.2/100,000/year and for women it was 1.2/100,000/year and 2.0/10,000/year for men and women respectively. A study from Glasgow showed an overall incidence of 7.2/100,000/year for SP (both PSP and PSP combined).
Age and sex distribution: PSP occurs preferentially among males with 80-89% of all PSP occuring in men. The male to female ratios are less striking for SSP. In a large Japanese study. The most common age of presentation for PSP in either sex was 20-30 years. In the younger age group of 10-19 years, there were more women as compared to men. Age distribution curves in this study were typically single peak, high rise types of curves with the peak falling in 20-30 years age bracket. From the age of 30 onwards, the curve showed a moderate fall with advancing age. The incidence of SSP rises with advancing age with a peak in 30-40 years age bracket and slowly declining afterwards. Two studies from Scotland have shown bi-phasic age distribution curves, with the first peak in the age bracket 20-30 (mainly PSP) and the second one in the 60-65 years (predominantly SSP)
Relation to smoking and physical characteristics: PSP occurs typically in tall and thin men who smoke. The risk of contracting pneumathroax rises with increasing height. The gradient with height is less pronounced among women and in SSP.
Smoking has been shown to increase the risk of PSP in a dose-response manner in a large Swedish study. The risk increases upto 9 fold for women and 22 fold for men. The life time risk for developing pneumathroax in this study was calculated as 12%, compared to 0.1% for never smokers. Studies from Japan and Netherlands have also shown similar results; 89% patients with SP in the Scottish study were smokers.
Relation to exercise: Onset of SP is not related to heavy exertion and muscle activity as was initially thought; most episodes of SP occur under resting conditions.
Relation to Whether conditions : Occurrence of SP has been related to fal in barometric pressure of at least 10 millibars / 24 hours. SP has also been reported among pilots in flights, Falling humidity levels have been related to increased occurrence of pneumothorax in a study from France. Another study from Scotland had reported low incidence of SP in the early summer months of May-July.
Right, Left or Bilateral ? Probably, SP occurs on both sides with equal frequency. Some studies have reported higher incidence on the right side (3:2), while others report left side to be more commonly involved. bilateral PSP is distinctly uncommon, occurring in only 2 out of over 25000 patients in a large study from Spain. In a Swiss study, Bilateral pneumothorax was seen in only 12 patients (4%) over 20 years and only 5 out of these were PSP. It is far more common is SSP; Especially those associated with AIDS and Pneumocystis carinii pneumonia (PCP) or cystic fibrosis.
Recurrence: The risk for recurrence is high. The first time recurrence rates vary between 20-60%. Risk increases with each subsequent episode. The risk for recurrence is more among taller persons. It is not related to BMI, size of pneumothorax or treatment of the initial episode. Smoking cessation reduces the risk as does the surgical pleurodesis after the initial episode.
Family history: A large Japanese study has demonstrated a positive family history of pneumathroax in 2.29% men and 4.42% women with PSP as compared to only 0.45% patients with SSP. Another study from Australia has however not shown any significant family history.
Aetiology of SSP: Until the description of PSP by Kjaegard (1932) tuberculosis was thought to be the leading cause of SP. It still probably is an important cause of SSP worldwide, especially in areas where tuberculosis has a high prevalence. AIDS and associated PCP is now emerging as a major cause of SSP. Other causes of SSP are pulmonary emphysema, pneumonia, primary and secondary malignancy, bronchial asthma, pulmonary fibrosis, cystic fibrosis, etc. Endometriosis (catamenial pneumothorax) and lymphangioleiomyomatosis are tow very rare causes of recurrent pneumothoraxes among women.
In children (<16 years), most of the SP are secondary and infection is the common leading cause. SP is very rare in infants and neonates and is always secondary to a precipitating illness.
Cystic Fibrosis (CF) and Pneumothorax: CF is an important cause of SSP in populations where it has high prevalence. Pneumothorax is a late and ominous complication of CF. Increased longevity of patients with CF has resulted in a concomitant increase in occurrence of pneumothorax. The overall incidence of pneumothorax in CF was found to be 0.7% among patients in the US Cystic Fibrosis Foundation (n=15569). The incidence rose form 0.1% in infants to 2.3% in patients over 31 years of age. One has to be cautious in offering pleurodesis to these patients as it can affect the subsequent possibility of lung transplantation. However, chances of recurrence are also high in these patients.
Dr. Dheeraj Gupta, MD, DM, FCCP
Deptt. of Pulmonary Medicine
Dr. Dheeraj Gupta