Safeway Sign

A middle age gentleman presents to your clinic complaining of pain in both legs when walking and standing still, relieved by sitting or lying down. On further questioning, you find that when he shops, he has to lean forward onto the shopping cart to relieve the pain. He also has discomfort, sensory loss, and weakness in both legs, but it is somewhat asymmetric and involves the entire leg. It is not in the distribution of any single nerve. There is associated mild low back pain. The neurologic exam is grossly normal.

Challenge: What's the diagnosis?

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