A diabetic patient presents with weakness of dorsiflexion and toe extension on the left foot, indicating a mononeuropathy of which nerve?

• A. Peroneal nerve
• B. Tibial nerve
• C. Sciatic nerve
• D. Sural nerve

Answer: (A)

The key idea is that dorsiflexion and toe extension are controlled by muscles innervated by the deep branch of the common peroneal (fibular) nerve. If this nerve is damaged, especially at the fibular neck where it’s vulnerable, you get foot drop with weakness of dorsiflexion and toe extension. In diabetes, a focal peroneal neuropathy is a well-recognized pattern. By contrast, the tibial nerve would mainly affect plantar flexion and toe flexion, the sural nerve carries sensory fibers only, and a sciatic nerve lesion would produce broader weakness affecting multiple leg muscles. So the presentation points to a peroneal nerve mononeuropathy.