<prompt> All are true about silicosis except?Bifringent crystals seenPleural plaque seenLower lobe is ussualy involvedMost common pnemoconiosis  <response>: Ans. c Lower lobe is ussualy involvedRef: Robbins 9thpg 689; 8thpg 687Silicosis involves upper lobe more commonly than lower lobe. Examination of the nodules by polarized microscopy reveals the birefringent silicate particles silica is weakly birefringent. 