Eosinophilic pneumonia, also known as eosinophilic pneumonitis is a rare disease where a type of white blood cell called an eosinophil accumulates in the lungs. The eosinophils accumulate in the air sacs of the lung, interfering with the transfer of oxygen. It can be acute, in which case the disease develops very quickly, or chronic, in which case its progression is far slower. In less developed countries, it's almost always set off by some type of parasitic infection. However, it can be set off in some patients by certain medications including such common ones as ibuprofen and ampicillin. It can also be caused by abuse of heroin or cocaine. However, many cases are idiopathic.
Because it's rare and its symptoms are more likely to be caused by other diseases, EP is a zebra diagnosis. It's most often mistaken for asthma and since both improve with steroids, a definitive diagnosis is often missed. However, EP will look different on x-rays and the eosinophil count is high in blood tests.
EP responds well to steroids, but in some cases patients may become dependent on the drugs. In addition, if the EP is caused by another underlying condition (such as parasites or cancer), the underlying condition usually has to be treated as well.