Can anorexia cause drop foot?

Doubtful but . . .: Foot drop (or drop foot) has a number of causes eg brain, spinal cord or nerve injury, which then can be broken down into physical & metabolic issues. Physical would be trauma eg severed nerve or compression from cast. Metabolic would be like diabetes. I suppose vitamin deficiency could do this but have not see any published data, just internet postings. So if anorexia leads to vitamin deficiency.

Yes: There are some reported cases in the literature. The reason is that the loss of subcutaneous fat around exposed nerves can cause pressure nerve palsies like the peroneal nerve at the head of the fibula (below the outside of the knee).