loss due to auditory tube dysfunction, sensorineural hearing loss (unclear mechanism) Oral cavity: strawberry gingivitis, underlying bone destruction with loosening of teeth, non-specific ulcerations throughout the lining of the mouth Trachea: subglottal stenosis Lungs: pulmonary nodules (referred to as "coin lesions"), infiltrates (often interpreted as pneumonia), cavitary lesions, bleeding in the lungs causing a person to cough up blood, and rarely bronchial stenosis. Arthritis: Pain or swelling (60%), often initially diagnosed as rheumatoid arthritis Skin: subcutaneous nodules (granulomas) on the elbow, purpura, various others (see cutaneous vasculitis) Nervous system: occasionally sensory neuropathy (10%) and rarely mononeuritis multiplex Heart, gastrointestinal tract, brain, other organs: rarely affected. Causes The cause of GPA is unknown, although microbes, such as bacteria and viruses, as well as genetics have been implicated in its pathogenesis. Pathophysiology Classic microscopic features of GPA include inflammation of blood vessels associated with poorly formed granulomas, necrosis, and many giant cells. Bacterial colonization with Staphylococcus aureus has been hypothesized as an initiating factor of the autoimmunity seen in people with GPA. Several genes involved in the immune system including PTPN22, CTLA4, and human leukocyte antigen genes may influence the risk of developing GPA. It is now widely presumed that the anti-neutrophil cytoplasmic antibodies (ANCAs) are responsible for the inflammation in GPA. The typical ANCAs in GPA are those that react with proteinase 3, an enzyme prevalent in neutrophil granulocytes. In vitro studies have found that ANCAs can activate neutrophils, increase their adherence to endothelium, and induce their degranulation that can damage endothelial cells. In theory, this phenomenon could cause extensive damage to the vessel wall, in particular of arterioles. Diagnosis Granulomatosis with polyangiitis is usually suspected only when a person has had unexplained symptoms for a long period of time. Determination of anti-neutrophil cytoplasmic antibodies (ANCAs) can aid in the diagnosis, but positivity is not conclusive and negative ANCAs are not sufficient to reject the diagnosis. More than 90% of people who have GPA test positive for ANCA. Cytoplasmic-staining ANCAs that react with the enzyme proteinase 3 (cANCA) in neutrophils (a type of white blood cell) are associated with GPA. Involvement of the ears, nose, and throat is more common in granulomatosis with polyangiitis than in the similar condition microscopic polyangiitis. If the person has signs of kidney involvement or cutaneous vasculitis, a biopsy is obtained from the kidneys. On rare occasions, thoracoscopic lung biopsy is required. On histopathological examination, a