Extensor Digitorum Brevis Innervated by the Tibial Nerve (All Tibial Foot): A case report

ABSTRACT

Innervation anomalies are well-known sources of erroneous interpretation in motor nerve conduction studies. The extensor digitorum brevis (EDB) muscle is supplied by the deep peroneal nerve and is commonly used as recording point in peroneal motor conduction study. If the compound muscle action potentials (CMAPs) are not evoked with EDB muscle recording without any symptoms or signs of peroneal neuropathy, we should lead one to consider either technical pitfall or anomalous innervation. We experienced an anomalous innervation in a woman in whom the bilateral EDB muscles were innervated exclusively by the tibial nerve. This was proved using a monopolar needle electrode for recording in extensor digitorum brevis (EDB) and flexor digitorum brevis (FDB) muscles, which encoded acceptable shape of CMAPs on tibial nerve stimulation. To avoid erroneous interpretation of electromyographic and nerve conduction studies, one should be aware of this possible innervation anomaly ("all tibial foot").