<prompt> A patient presents with melaena normal renal function, hypeension and mononeuritis multiplex. The most probable diagnosis is:Classical polyaeritis nodosaMicroscopic polyangiitisHenoch-Schonlein purpuraBuergers disease  <response>: Answer is A Classic PAN : Amongst the options provided, mononeuritis multiplex is a feature of classical PAN and microscopic polyangitis. Presence of hypeension infrequent in microscopic polyangitis and normal renal function infrequent in microscopic polyangitis leads us to a diagnosis of classical polyaeritis nodosa. Renal involvement in classic PAN Pathology in kidney is that of aeritis without glomeruionephritis involves small medium sized muscular aeries Renal impairment is uncommon-- Hypeension is frequent Renal involvement is mainly in the form of Renovascular hypeension . Renal involvement in microscopic polyangitis Pathology in kidney is that of glomerulonephritis Rapid renal impairment is characteristic-- API 7th1183 Hypeension is infrequent-API 7th1183 Causes of mononeuritis multiplex : Common causes Uncommon causes Classic polaeritis nodosa Mixed cryoglobulinemia Microscopic polyangitis Sjogren syndrome RA Wegners granulomatosis SLE Progressive systemic sclerosis Mixed connective tissue disease Churg-strauss allergic granulomatosis Hypersensitivity angitis Leprosy Amyloidosis Diabetes 