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Vrms/T quantitation: usefulness in patients with neuropathies
1Department of Neurology Hines VAH, Illinois 60141, USA.
Muscle & Nerve
|December 1, 1995
Summary
The root mean square voltage (Vrms)/turns (T) ratio effectively identifies neuropathies. This sensitive measure, requiring no direct tension, aids in diagnosing neurogenic dysfunction when other tests are normal.
Area of Science:
- Neurology
- Electromyography
- Nerve Conduction Studies
Background:
- Neuropathic disorders present diagnostic challenges.
- Electromyography (EMG) is crucial for evaluating nerve and muscle function.
- Standard EMG parameters may not always detect subtle neurogenic dysfunction.
Purpose of the Study:
- To evaluate the diagnostic sensitivity of the root mean square voltage (Vrms)/turns (T) ratio in identifying neuropathies.
- To determine if Vrms/T ratio measurements can enhance the electrodiagnostic evaluation of neurogenic dysfunction.
Main Methods:
- Data collected using concentric needle electrodes from biceps brachii, first dorsal interosseous, tibialis anterior, and calf muscles.
- Recordings analyzed from 35 normal subjects and 24 patients with suspected neuropathic disorders.
- Vrms/T values calculated from four needle sites during strong muscle contractions (<80% maximum tension).
Main Results:
- Mean Vrms/T values ≥ 1.0 were significantly more frequent in patients (p < 0.012-0.0001).
- In 13 muscles, elevated Vrms/T was the sole abnormality on needle EMG.
- An elevated Vrms/T ratio was found in 10/14 muscles with suspected abnormalities but normal conventional EMG and nerve conduction studies.
Conclusions:
- The Vrms/T ratio is a sensitive indicator for detecting neuropathies.
- Vrms/T measurements provide valuable supplementary information in electrodiagnostic evaluations.
- This ratio can identify neurogenic dysfunction missed by standard EMG parameters and nerve conduction studies.