This is a progressive disease usually and hence needs frequent periodic monitoring. Long term exposure to
pollutants like silica, asbestos, animal droppings, dust, pollens etc can cause this. Other reasons are GERD, certain medications like cancer medicines, some heart medicines or some antibiotics and certain diseases like Sjogren's syndrome, systemic lupus erythematosus, tuberculosis, rheumatoid arthritis, pneumonia, dermatomyositis, polymyositis, and sarcoidosis.