An electrophysiological severity scale in tarsal tunnel syndrome

To propose a neurophysiological classification of tarsal tunnel syndrome.

We retrospectively reviewed the medical records of two electromyography laboratories. Case inclusion criteria were based on clinical parameters. Motor conduction velocity, distal motor latency (DML), sensory conduction velocity (SCV) and sensory action potential (SAP) from big toe (T1) and from fifth toe (T5) to medial malleolus were measured in the medial and plantar nerves. When SCVs of T1 and T5 were normal, we considered the difference in T1 SCV between affected and unaffected side and in T1 SCV of the affected side with sural nerve distal SCV. Feet with TTS were classified in six electrophysiological classes: 0, normal SCV and DML; 1, normal absolute SCV with abnormal comparative tests; 2, slowing of T1 and T5 SCV and normal DML; 3, slowing of SCV and DML; 4, absence of T1 and T5 SAPs and abnormal DML; 5, absence of sensory and motor response.

A total of 111 feet belonging to 96 patients (27 men, 69 women; mean age 49.6 years) were diagnosed with TTS. T1 and T5 SCV were abnormal in 82 and 73% of cases, respectively, and comparative tests were abnormal in a further 7% of cases. DML was abnormal in 82 feet (73.9%). Eight feet (7%) were without neurographic abnormalities. The distribution of feet in neurophysiological classes was: stage 0, 7%; stage 1, 9%; stage 2, 10%; stage 3, 39%; stage 4, 32%; stage 5, 3%. Higher clinical scores coincided with higher neurographic classes.

The progression of neurographic abnormalities in TTS reflects the relation between SCV and DML, and between neurographic values and clinical severity. The scale assigns severity classes in a reliable and non-arbitrary way. This classification can easily be used by electrophysiological laboratories with their own electrophysiological techniques and normal values.