Leg Pain During Exercise or Driving

A 26-year old male, who is a long-distance runner, presents to his doctor complaining of right foot pain during aerobic exercise in the last two months. He says that the pain exacerbates with training and he is now unable to tolerate even mild aerobic exercise. He is afraid that he will not be able to participate in the upcoming annual marathon scheduled for next month in his city, due to his frustrating symptoms. Further evaluation reveals that pain of his right foot is accompanied by right calf tightness, paresthesia and it is reproduced after running less than 100 meters. The pain is relieved within seconds to minutes after cessation of exercise. Occasionally when he drives his car for a long time, he feels numbness and coldness at his calf. He has noticed that these symptoms are produced with knee extension when the foot is plantar flexed. Last month he visited an orthopedic surgeon, who prescribed him analgesics and recommended physical therapy. However, despite the patient's adherence to medical instructions, the pain has not subsided. His last month knee MRI was unremarkable. Physical exam reveals patent femoral, popliteal and dorsal foot arteries and normal ankle-brachial-index (ABI). Pain is not reproduced with palpation, but it is elicited with sustained passive dorsiflexion and plantarflexion of the foot. The patient does not smoke and drinks alcohol only on weekends. There is no family history for cardiovascular diseases and his BMI is 25. He is a vegetarian and consumes protein supplements.

Which of the following is the most likely diagnosis?

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