What is A 50-year-old man has had a chronic cough for the past 18 months. Physical examination shows nasopharyngeal ulcers, and the lungs have diffuse crackles bilaterally on auscultation. Laboratory studies include a serum urea nitrogen level of 75 mg/dL and a creatinine concentration of 6.7 mg/dL. Urinalysis shows 50 RBCs per high-power field and RBC casts. His serologic titer for C-ANCA (proteinase 3) is elevated. A chest radiograph shows multiple, small, bilateral pulmonary nodules. A transbronchial lung biopsy specimen shows a necrotizing inflammatory process involving the small peripheral pulmonary arteries and arterioles. Which of the following is the most likely diagnosis? and explain in detail?
Anti-neutrophil cytoplasmic autoantibody (ANCA)- associated vasculitis (granulomatosis with polyangiitis) is a form of hypersensitivity reaction to an unknown antigen characterized by necrotizing granulomatous inflammation that typically involves small to medium-sized vessels, although many organ sites may be affected. Pulmonary and renal involvement can be life-threatening. C-ANCAs (antibodies mainly directed against neutrophil proteinase 3) are found in more than 90% of cases. Fibromuscular dysplasia is a hyperplastic medial disorder, usually involving renal and carotid arteries; on angiography, it appears as a "string of beads" caused by thickened fibromuscular ridges adjacent to less involved areas of the arterial wall. Granuloma pyogenicum is an inflammatory response that can produce a nodular mass, often on the gingiva or the skin. Kaposi sarcoma can produce plaque-like to nodular masses that are composed of irregular vascular spaces lined by atypical-appearing endothelial cells; skin involvement is most common, but visceral organ involvement can occur. Polyarteritis nodosa most often involves small muscular arteries, and sometimes veins. It causes necrosis and microaneurysm formation followed by scarring and vascular occlusion, mainly in the kidney, gastrointestinal tract, and skin of young to middle-aged adults. Takayasu arteritis is seen mainly in children and involves the aorta (particularly the arch) and branches such as the coronary and renal arteries, with granulomatous inflammation, aneurysm formation, and dissection.