Hypersensitivity Pneumonitis (HP) is an environmental disease of the lung alveoli (not the bronchi; see Diagram — Lower Respiratory Tract), caused by something inhaled. It may seem like asthma in terms of coughing episodes that come and go, but requires completely different management.
HP is common among farmers [“farmer’s lung”], especially in humid climates, & perhaps also common among bird fanciers [“pigeon breeder’s lung” — people who keep birds, not just “fancy” them]. Outbreaks of HP have occurred among office workers [“humidifier lung”], lifeguards [“lifeguard lung”], & autoworkers. There are long lists of irritants such as “mushroom worker’s lung,” “paprika slicer’s lung,” “sauna-taker’s lung,” “mummy handler’s lung,” “bible printer’s lung,” etc….. The problem is, these substances don’t just “irritate” the lung, like with asthma, but cause long-term damage that often won’t get better, & keeps getting worse.
The key to diagnosis of HP depends on a history of jobs and hobbies. Symptoms of cough, shortness of breath, fatigue, fever, and/or nausea begin 4-8 hours after being exposed to the offending particles, and go away in 12 hours to several days after the exposure is gone. If we hear crackles (“rales”) with a stethoscope, there’s more chance it’s HP. Wheezes are rare.
Chest X-ray is usually normal until the disease is advanced; the same with pulmonary function tests. Commercial laboratory blood tests are unreliable. Weight loss is an ominous sign. If you have symptoms fitting the above pattern, ask your health care provider for a list of possible environmental causes, in case one matches. Unfortunately, HP is one of those conditions which lack easy diagnosis until irreversible damage has occurred.
A specific type of chest CT scan (“high-resolution CT”) may point to the diagnosis, but may also be normal at a point where treatment is still possible. Farmers who don’t easily respond to asthma inhalers, and other patients exposed to specific substances, should see a pulmonologist (lung specialist). The specialist may know a lab that can concoct a custom-made “brew” of the patient’s actual exposure and run immunologic tests. Various medications can help HP, but the best treatment of all is identifying & avoiding the cause.