How do you record palmar sensory findings of the ulnar nerve with a nerve conduction study (NCS)?

Recording Palmar Sensory Findings of the Ulnar Nerve with Nerve Conduction Study

To record palmar sensory findings of the ulnar nerve, use an orthodromic technique with ring electrodes placed on the hypothenar palm (active electrode over the ulnar nerve 10cm proximal to the wrist, reference 3-4cm more proximal), stimulating the ulnar palmar cutaneous nerve at the hypothenar eminence and recording proximally at the wrist. 1

Technical Setup and Electrode Placement

Recording Configuration

• Place the active recording electrode over the ulnar nerve 10cm proximal to the wrist crease 1
• Position the reference electrode 3-4cm more proximal along the ulnar nerve course 1
• Use surface recording electrodes for optimal signal capture 1

Stimulation Site

• Stimulate at the hypothenar palm to activate the ulnar palmar cutaneous nerve (UPCN) 1
• The UPCN provides sensory innervation specifically to the hypothenar palm, making it useful for localizing distal ulnar nerve pathology 1
• This nerve branches proximal to Guyon's canal, allowing differentiation between proximal and distal ulnar nerve lesions 1

Normal Values and Interpretation

Expected Measurements

• Normal distal latency: 2.19 ± 0.17 milliseconds 1
• Normal distal amplitude: 12.7 ± 6.9 microvolts 1
• These values are based on orthodromic sensory conduction technique from the hypothenar palm 1

Clinical Utility

• This technique can demonstrate injury to the superficial sensory branch of the ulnar nerve while showing sparing of the UPCN 1
• The palmar cutaneous branch is particularly useful in cases of distal ulnar nerve pathology at or distal to the wrist 1
• When combined with dorsal ulnar cutaneous nerve testing, this provides comprehensive assessment of ulnar sensory branches 2

Additional Palmar Stimulation Techniques

Mixed Nerve Studies

• For suspected ulnar neuropathy at the wrist, add a palmar stimulation site when recording from first dorsal interosseous (FDI) 3
• Stimulate at both the wrist and palm, recording from FDI to calculate wrist-palm conduction velocity 3
• Wrist-palm FDI conduction velocity below 37 m/s is abnormal and specific for ulnar neuropathy at the wrist 3
• This technique demonstrates conduction block, which is an important cause of muscle weakness in ulnar neuropathy at the wrist 3

Comparative Studies

• The median-to-ulnar mixed nerve latency difference from palmar stimulation (PM-PU) is abnormal when ≥0.5 ms 4
• This comparative technique has 56% sensitivity for detecting mild nerve pathology 4
• Palmar mixed nerve studies complement pure sensory studies by assessing both sensory and motor fibers 4

Common Pitfalls to Avoid

Technical Considerations

• Volume conduction to multiple ulnar nerve branches can occur, potentially confounding results 1
• Use a modified collision technique when needed to verify isolation of the UPCN 1
• Ensure adequate distance (10cm) between stimulation and recording sites to allow accurate latency measurement 1

Interpretation Caveats

• The UPCN technique requires further validation as it cannot always be electrophysiologically isolated in all subjects 1
• Always correlate palmar sensory findings with dorsal ulnar cutaneous nerve studies and motor studies to FDI and abductor digiti minimi for complete localization 3, 5
• Normal distal motor latency to FDI should not exceed 4.5 ms, and side-to-side difference should not exceed 1.3 ms 5