ORIGINAL ARTICLE Sensory Nerve Conduction in Branches of Common Interdigital Nerves: A New Technique for Normal Controls and Patients With Morton’s Neuroma Burhanettin Uludag,* Cengiz Tataroglu,† Fikret Bademkiran,* I ˙ rem Fatma Uludag, and Cumhur Ertekin* Abstract: In this article, a new electrodiagnostic approach is described for patients with Morton’s neuroma. The new method is based on the anatomic fact that the two branches of the common plantar interdigital nerves innervate the lateral side of one toe and the medial side the next one. This study included 20 normal subjects (aged 28 –58 years, 10 men and 10 women) and 4 patients with Morton’s neuroma (aged 44 –52 years, 4 women). The branches of adjacent common plantar interdigital nerves that innerve one toe were stimulated superficially and separately with half of one toe covered with a piece of medical tape. The recordings were obtained on the posterior tibial nerve at the medial malleolus with needle electrodes. Thus, the difference in latencies of obtained sensory nerve action potentials on the posterior tibial nerve with needle electrode was measured. From normal subjects’ data, it was determined that a latency difference value of above 0.17 milliseconds (mean  2.5 SD) in one toe was abnormal. All of the patients with Morton’s neuroma showed abnormal interlatency difference values. This new method, which we have developed, is more sensitive, simple to use, does not require extra equipment, and does not cause excessive pain. We suggest that interlatency difference between branches of the common plantar interdigital nerves is a useful and sensitive method for the diagnosis of Morton’s neuroma. Key Words: Common plantar interdigital nerve, Electrodiagnosis, Metatar- salgia, Morton’s neuroma, Nerve conduction. (J Clin Neurophysiol 2010;27: 219 –223) M orton’s metatarsalgia or Morton’s neuroma (MN) refers to interdigital neuropathies of the foot. This syndrome results from damage to an interdigital nerve where it lies between the heads of adjacent metatarsal bones, just before it divides into two digital nerves. The nerve most often involved lies between the third and fourth metatarsals (Dumitru and Zwarts, 2002; Morton, 1876; Stew- art, 2000; Wu, 2000). That plantar interdigital nerves are pinched between the heads of the adjacent metatarsals is widely accepted. Alternatively, the nerve is pressed against and stretched across the firm anterior edge of the deep transverse metatarsal ligament (Stew- art, 2000). At operation, a fibrous nodule is found in the interdigital nerve near the metatarsal heads. It is often called a neuroma, but this is a misnomer because the swelling consists of fibrous rather than neural tissue (Dumitru and Zwarts, 2002; Guiloff et al., 1984). Nerve conduction studies can be performed by stimulating the digital nerves in the toes and recording with needle electrodes from the tibial nerve at the ankle (Almeida et al., 2007; Falck et al., 1984; Guiloff et al., 1984; Oh et al., 1984). However, the sensory nerve action potentials (SNAP) are small and averaging is required. These electrophysiologic methods were unpleasant for the patient and time consuming. MN can be imaged by neuroimaging methods including ultrasonography, computed tomography, and magnetic resonance imaging (MRI) (Redd et al., 1989; Turan et al., 1991; Zanetti et al., 1997, 1999). In this article, a new electrodiagnostic approach is described for patients with MN. The new method is based on the anatomic fact that the common plantar interdigital nerves (IDNs) have two branches, which innervate the lateral side of one toe and the medial side the next one. Therefore, it is possible to stimulate the lateral and medial side of the third toe separately and superficially by using a medical plaster covering the toe’s medial and lateral aspects respec- tively. The needle recording site is at the ankle from the posterior tibial nerve (PTN), similar to previous studies (Falck et al., 1984; Oh et al., 1984). MATERIALS AND METHODS This study included 25 normal subjects (mean age: 45  9.2 years; range: 28 –59 years, 15 women and 10 men) and 10 patients with MN or metatarsalgia (mean age: 44  3.4 years, range: 34 – 62 years, 8 women, 2 men). The normal subjects were divided into two age groups; 28 – 44 years and 45–59 years. We studied 31 feet in 25 normal subjects. None of the normal subjects had subjective or objective symptoms of peripheral sensory abnormalities. We performed standard neurologic examination and routine electromyography including sural, peroneal, and PTN conduction velocities for each subject. All of the patients had symptoms of MN such as neuralgic pain or numbness on the bottom of the foot, and tenderness with compression on the third interdigital space. In addition, MRI of the affected foot was performed on all patients with MN. All electrodiagnostic study was made by Nicolet Viking IV EMG machine. For motor and sensory nerve conduction velocity, standard bandpass, gain, sweep time, and stimulus settings were used on the EMG device (for sensory nerve conduction velocity, 20 Hz–5 kHz, 10 V/div, 20 milliseconds and 0.1 milliseconds dura- tion; for motor nerve conduction velocity, 20 Hz–5 kHz, 2 mV/div, 10 or 20 milliseconds and 0.2 milliseconds, respectively). The Stimulation Procedure A standard ring electrode (Medtronic 9013S0301) was placed around third and fourth toes with interelectrode distance of at least 10 mm for stimulation of branches of IDNs. Because the aim of this study was to obtain a sensory action potential from one of the two branches of the IDN, we devised a special method, called tape method for sake of brevity (Fig. 1A). In the toe investigated, a piece From the *Neurology Department of the Medical School of Ege University, Bornova, I ˙ zmir, Turkey; †Neurology Department of the Medical School of Adnan Menderes University, Aydin, Turkey; and Neurology Clinic of Tepecik Research and Education Hospital, I ˙ zmir, Turkey. Address correspondence and reprint requests to Burhanettin Uludag, MD, Depart- ment of Neurology and Clinical Neurophysiology, Ege University Hospital, 35100, Bornova, I ˙ zmir, Turkey; e-mail: burhanettin.uludag@ege.edu.tr. Copyright © 2010 by the American Clinical Neurophysiology Society ISSN: 0736-0258/10/2703-0219 Journal of Clinical Neurophysiology • Volume 27, Number 3, June 2010 219