| 1 | Due to the lung involvement itself (e.g. Sjögren’s syndrome, Wegener’s disease, systemic sclerosis, Churg–Strauss syndrome, idiopathic interstitial pneumonias and sarcoid) |
| 2 | Due to the treatment (drug induced cough: methotrexate, cyclophosphamide) |
| 3 | Due to infections in the immunocompromised host |