ELECTROPHYSIOLOGICAL STUDY OF THE TIBIAL NERVE ACROSS THE TARSAL TUNNEL IN DISTAL SYMMETRIC DIABETIC POLYNEUROPATHY.

OBJECTIVE To demonstrate abnormalities of motor conduction of the tibial nerve across the tarsal tunnel (TT) in type 2 diabetes. DESIGN 124 consecutive patients (mean age 66.6 years, 62.1% males) with distal symmetric diabetic polyneuropathy (DSDP) clinically diagnosed were prospectively enrolled. Nerve conduction studies (NCS) of deep peroneal, tibial, superficial peroneal, medial plantar, and sural nerves, and standard needle electromyography in the lower limbs were performed. Demographic, anthropometric and clinical findings were collected. RESULTS Motor conduction velocity (MCV) of the tibial nerve across TT was slowed in 60.5% of patients; another 4% showed conduction block across TT without reduction of MCV. Overall percentage of abnormalities across TT (64.5%) exceeds that of the sensory conduction velocities of proximal sural and superficial peroneal nerves. Abnormal tibial MCV across TT represents the most common abnormality among all motor NCS parameters and significantly correlates with HbA1c level, diabetic neuropathic index score and diabetic complications frequency. CONCLUSIONS Tibial conduction abnormalities across TT are the most sensitive motor parameter in DSDP, second only to conduction abnormalities of sensory/mixed distal nerves of the feet. The employ of NCS across TT of the tibial nerve may be useful in the electrophysiological protocol to confirm the diagnosis of DSDP.