Monophasic Waveforms in Nerve Conduction Studies
Monophasic waveforms detected in nerve conduction studies indicate severe peripheral vascular disease with compromised arterial flow, NOT a neurophysiological finding—this question appears to confuse vascular Doppler ultrasound terminology with nerve conduction study terminology.
Critical Clarification
The term "monophasic waveforms" is vascular terminology used in Doppler ultrasound studies to describe arterial blood flow patterns, not a nerve conduction study finding. In the context provided (right ulnar left proximal), this appears to be describing:
- Vascular assessment: Monophasic arterial waveforms indicate severe arterial stenosis or occlusion with loss of normal triphasic flow patterns
- Clinical significance: This represents compromised arterial perfusion requiring urgent vascular evaluation
If This Were Actually a Nerve Conduction Study Finding
If you are asking about abnormal nerve conduction patterns in the ulnar nerve, the relevant findings would be:
Axonal vs. Demyelinating Patterns
Axonal neuropathy primarily affects compound muscle action potential (CMAP) amplitudes rather than producing "monophasic" patterns 1. Key features include:
- Reduced CMAP amplitudes with relatively preserved conduction velocities 2
- Normal or near-normal distal latencies and F-wave latencies 3
- In severe cases with reduced amplitude, conduction velocity rarely falls below 80% of lower limit of normal 3
Demyelinating neuropathy produces 1:
- Slowed nerve conduction velocities (30-50% reduction from normal) 4
- Prolonged distal latencies (35-70% above normal) 4
- Temporal dispersion or conduction blocks 2
- F-wave latency prolongation (120-150% of upper limit) 4
Specific Ulnar Nerve Considerations
Nerve conduction studies can identify 1:
- Mononeuropathies (focal entrapment at elbow or wrist)
- Differentiation between axonal versus demyelinating pathology 2
- Multiple mononeuropathy versus polyneuropathy patterns 1
Clinical context matters: NCS should be performed after 4-6 weeks of conservative management if symptoms persist or remain unclear 5. EMG has poor sensitivity (56% of cases show no EMG abnormality despite imaging-confirmed compression) 5.
Immediate Action Required
If monophasic waveforms were truly detected on vascular Doppler: Urgent vascular surgery consultation is needed to assess for critical limb ischemia and potential need for revascularization.
If this is a mischaracterized NCS finding: Review the actual nerve conduction parameters (amplitudes, velocities, latencies) to properly classify as axonal versus demyelinating pathology 2, 4.