Possible etiologies of UIP include IPF, rheumatoid arthritis, systemic sclerosis, poly/dermatomyositis, mixed connective tissue disease, medication induced, ANCA associated vasculitis, asbestosis. The main differential diagnosis for the UIP pattern is the NSIP pattern. The presence of honeycombing is practically diagnostic of UIP. Note that honeycombing is not just intralobular septal thickening, there is no architecture inside the cystic areas, no central bronchiole or arteriole and they do not represent dilated airways.