We have described an unusual case of drug-induced EP. There are only 42 cases of mesalazine-induced EP available from 1991 to 20152. According to a summary of mesalazine-induced lung diseases3, among patients who developed EP results from mesalazine, the usual period from initial dose to symptom onset is within one month (4 out of 9), some (4 out of 9) patients developed symptoms from 1 month to 1 year, only one patient developed symptoms longer than one year since initiating mesalazine. Our patient has a period of 5 years between the first dose of mesalazine and the onset of EP, which is quite rare.
EP, also known as pulmonary infiltrates with eosinophilia syndrome, can be either primary and secondary. The etiology of EP remains unknown. Drugs, toxins and parasite infection are all important causes of secondary EP. Daptomycin, sulfasalazine and mesalazine are common culprits4.
Although the pathogenesis is not fully understood, lung involvement in IBD patients is not uncommon. Abnormal pulmonary function test is noted in 25% Crohn's disease (CD) patients and 6% UC patients; abnormal chest CT scan is seen in 50% of patients with IBD5. 20–55% of patients with IBD suffer from latent interstitial pulmonary involvement, among which drug-induced lung disease is most common1. EP in IBD patients most commonly occurs in patients taking sulfasalazine. However, although relatively rare, EP also can be caused by mesalazine and methotrexate6.
A diagnosis of drug-induced EP should be suspected in a patient with an abnormal chest CT scan and peripheral, bronchoalveolar lavage, or lung tissue eosinophilia, especially in patients using sulfasalazine or mesalazine. Lung biopsy is rarely required7.
Due to the rarity of the complication, mesalazine-induced EP is often misdiagnosed. Marked peripheral, bronchoalveolar lavage eosinophilia and a CT image suggestive of EP are all clues to the diagnosis of EP. A prompt recovery can be expected after discontinuing the causative drug8.