<prompt> Most common cause of gangrene of foot of 30 years old farmer who is a chronic smoker -Raynauds diseaseMyocardial infarctionAtherosclerosisThromboangitis obliterans  <response>: All four can cause gangrene Myocardial infarction can cause gangrene by thromboembolismLets see, each option one by one.Raynauds disease Is ds of young women F:M ratio is 5:1commonly the upper limbs are affected specially the fingers the thumb is generally escapedThe disease is characterized by Raynauds phenomenon which is a series of attacks ofLocal syncope digits become cold and whiteLocal asphyxia digits turn blue with burning sensationLocal recovery digits regain normal colourPulses remain unaffected as this is the disease which affects arteriolesWith the help of points a and b Raynauds ds can be ruled out.Atherosclerosis Senile gangreneSeen in elderly people over 50 years of age.Thus because of age factor we can rule out atherosclerosis.Myocardial infactionAge factor again helps in ruling it out as MI is generally seen in elderly, though its incidence is increasing in young, but it cannot be a more common cause than Buergers disease.Buergers Thromboangitis obliterans Usual victims of this ds are young men below 40 yrs of age, who are smokers ds is not seen in females and nonsmokers.Buerger ds is the inflammatory reaction in the arterial wall with involvement of the neighbouring vein and nerve, terminating in thrombosis of the artery.It characterstically involves small and medium sized arteries plantars, tibial and radial arteryBoth upper and lower extremities are affected.In lower extremity the ds. occurs beyond the popliteal artery. In upper extremity the ds occurs beyond the brachial art.Early in the course of Buergers ds the superficial veins are involved producing the characterstic migratory, recurrent superficial thrombophlebitis.An imp difference with atheroselerosis is that, atherosclerosis is a disease of large sized arteries, buergers is a ds of small arteries. 