What is the role of nerve conduction studies in diagnosing and managing tarsal tunnel syndrome?

Nerve Conduction Studies in Tarsal Tunnel Syndrome

Nerve conduction studies (NCS) are useful for confirming the diagnosis of tarsal tunnel syndrome but have limited sensitivity, and a negative test does not exclude the diagnosis. 1

Diagnostic Role and Limitations

Evidence Quality and Recommendations

• NCS may be useful for confirming tibial neuropathy at the ankle (Level C recommendation), but well-designed studies evaluating their definitive utility remain lacking 1
• The actual sensitivity and specificity of NCS in tarsal tunnel syndrome cannot be precisely determined from available evidence 1
• Sensory nerve conduction studies are more likely to be abnormal than motor studies, though exact diagnostic accuracy remains unclear 1

Clinical Performance

• In clinically suspected idiopathic tarsal tunnel syndrome, motor NCS demonstrated 80% sensitivity but only 33.3% specificity, making it more useful as a screening tool than a definitive diagnostic test 2
• NCS abnormalities were found in 80% of symptomatic limbs and 66.6% of asymptomatic limbs in patients with clinical tarsal tunnel syndrome 2
• Abnormally slow nerve conduction through the posterior tibial nerve typically predicts failure of conservative treatment, making NCS valuable for prognostication 3

Technical Considerations

Specific Testing Approaches

• Across-tarsal-tunnel motor nerve conduction technique allows differentiation between proximal tarsal tunnel compression versus distal plantar nerve compression 4
• For medial plantar nerve, the mean + 2SD across-tunnel onset latency is 3.2 msec with peak latency of 2.9 msec 4
• For lateral plantar nerve, across-tunnel onset latency is 3.2 msec with peak latency of 2.9 msec 4

Enhanced Diagnostic Yield

• Electrodiagnostic triple compression stress test (placing ankle in full plantar flexion and foot in inversion with pressure over posterior tibial nerve) increases sensitivity when basic nerve conduction results are negative 5
• This stress test was positive in 78 feet where basic studies may have been negative, identifying 11 additional cases with false negative clinical examination 5

Role in Management Decisions

Surgical Planning

• A positive Tinel's sign before surgery combined with abnormal NCS is a strong predictor of successful surgical decompression 3
• NCS helps identify the specific location and nature of nerve compression (demyelination versus axonopathy), with demyelination being slightly more common in idiopathic cases 2
• Probable demyelination was identified in 58.2% of electrophysiologically abnormal nerves in symptomatic limbs 2

Monitoring Considerations

• For patients with peripheral motor neuropathy, serial neurologic examinations are recommended over repeated electromyography/nerve conduction studies for monitoring disease activity 6, 7
• Early in disease, all electrodiagnostic studies may be normal, requiring repeat testing in 3-4 weeks if clinical suspicion remains high 8

Common Pitfalls

• Do not rely solely on NCS to exclude tarsal tunnel syndrome—the diagnosis remains primarily clinical, based on symptoms of distal foot pain with nocturnal exacerbation, positive Tinel's sign, and sensory changes in the distribution of the posterior tibial nerve 3, 1
• Ultrasound of the foot may be performed when there is high clinical suspicion, as it can identify space-occupying lesions, anatomic variants, and nerve enlargement 6
• Heel pain does not correlate well with abnormal inferior calcaneal nerve conductions, so negative studies in patients with isolated heel symptoms should not exclude the diagnosis 2
• NCS is most valuable when positive (confirming diagnosis and guiding treatment), but negative studies require clinical correlation and do not rule out tarsal tunnel syndrome 1