A 20 year old male smoker is noted to have intense rubor of the feet and absent foot pulse. Examination: amputated right 2nd toe. What is the most probable diagnosis?

The key is C. Buerger’s disease. [ The traditional diagnosis of Buerger's disease is based on 5 criteria (smoking history, onset before the age of 50 years, infrapopliteal arterial occlusive disease, either upper limb involvement or phlebitis migrans, and absence of atherosclerotic risk factors other than smoking). As there is no specific diagnostic test and an absence of positive serologic markers, confident clinical diagnosis should be made only when all these 5 criteria have been fulfilled].