A 45 year old man who is a known hypeensive complains of fever, migraine, loss of appetite, myalgia and presented with ulcerations on the calf and near the malleoli. On examination, splinter haemorrhages and palpable purpura were noted. On CT angiography, aneurysm and stenosis of medium sized vessels were observed. The type of hypersensitivity to this condition is

The most likely diagnosis is polyaeritis nodosa which is an example of Type III hypersensitivity reaction. In type III hypersensitivity, immune complexes may deposit in tissues or blood vessels, and elicit an acute inflammatory reaction by activating the complement system. The inflammatory reaction causes tissue injury. The pathogenesis of systemic immune complex disease can be divided into three phases: Formation of immune complexes Deposition of immune complexes Inflammation and tissue injury. Type III hypersensitivity reactions Post-streptococcal glomerulonephritis SLE Polyaeritis nodosa Reactive ahritis Serum sickness Ahus reaction Farmer's lung Hypersensitivity pneumonitis Type II lepra reaction Henoch Schonlein purpura Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition