How do we categorize pneumothorax?

There have been several cases of pneumothorax on the wards recently. How do we classify them?

This was addressed in a review in the December 2021 issue of Clinics in Chest Medicine entitled Pneumothorax.  The article is behind a paywall but free tull text is available to UAMS residents in Clinical Key.

Here are some of the main points from that review:

Pneumothorax that's not iatrogenic or traumatic is designated spontaneous pneumothorax. This category is further subdivided into primary and secondary spontaneous pneumothorax. Primary spontaneous pneumothorax refers to spontaneous pneumothorax in those patients with no clinically apparent lung disease.  Secondary spontaneous pneumothorax is designated in those patients with known lung disease. Here it gets a little confusing because the British Thoracic Society guidelines categorize all smokers and all patients greater than 50 years of age in the secondary category with or without known underlying lung disease.

Assuming smokers without clinically apparent lung disease are classified as primary, tobacco smoking is the strongest risk factor for primary spontaneous pneumothorax. After an episode of primary spontaneous pneumothorax in smokers, cessation reduces the recurrence rate four fold.

Height and male sex are also risk factors for primary spontaneous pneumothorax. Tall men have increased apical plural stretching. However, when increased height is part of a heritable disorder of connective tissue such as Marfan or certain types of Ehlers Danlos syndrome, associated pneumothoraces are designated as secondary.

Any type of pulmonary disease can be a risk factor for secondary spontaneous pneumothorax but COPD is the main one. Tuberculosis is the most common underlying disorder in endemic areas and was a significant cause historically. Many other infections can be associated with secondary spontaneous pneumothorax. PJP is well known. Bacterial pneumonias that cause necrosis can be associated with secondary spontaneous pneumothorax including staphylococcus, klebsiellla, pseudomonas, and anaerobes.  Covid can cause pneumothorax.  In non mechanically ventilated patients the frequency is around 1%.  Higher rates, not surprisingly, are seen in mechanically ventilated covid patients.

Less common causes of secondary spontaneous pneumothorax are the cystic lung diseases including lymphangioleiomyomatosis, Langerhans cell histiocytosis, and catamenial pneumothorax. Each individual cause is rare but together they account for a significant minority.  There are other examples of these which would be appropriate for a more narrowly focused review.

Recurrence of spontaneous pneumothorax is common across the board.  Prevention strategies are detailed in the article.

Topics for deeper dives:  Cystic lung diseases; tuberous sclerosis comples (a factor in many cases of lymphangioleiomyomatosis).