[Significance of electroneurographic parameters in the diagnosis of chronic neuropathy of the ulnar nerve at the elbow]

Abstract

Purpose: Ulnar neuropathy at the elbow (UNE) is the second most common compressive neuropathy of the upper limb. Besides clinical evaluation, electrodiagnostic studies are usually applied to confirm the diagnosis. However, there are certain limitations to the diagnosis of UNE by electrodiagnostic studies. In a prospectively performed study we compared the diagnostic value of the electrodiagnostic parameters to the symptoms and the clinical parameters for different degrees of sensory and motor dysfunctions.

Methods and materials: Between 2001 and 2003, 38 patients (mean age 53.9 +/- 8.8 years, 19 men and 19 women) were treated at our institution for UNE. For 34 (89%) patients complete electrodiagnostic studies were performed and for 25 patients there was also an electrodiagnostic evaluation of the asymptomatic contralateral arm. According to the symptoms and clinical parameters (grip and pinch grip, two-point discrimination), the patients were assigned to three stages (mild, moderate, and severe). Electrophysiological measurements for each stage were compared with one another. The diagnostic value for each electrophysiological parameter was evaluated in comparison to the normal limits of the "Deutsche Gesellschaft für Neurologie (DGN)" and the "American Association of Electrodiagnostic Medicine (AAEM)".

Results: In the 34 symptomatic arms the mean values for motor nerve conduction were: conduction velocity (MNCV) = 41.2 +/- 11.6 m/s; velocity change above-to-below-elbow segment = 12.8 +/- 7.7 m/s; CMAP = 9224 +/- 5514 microV; dL = 3.24 +/- 0.82 mg. For the moderate stages of nerve compression (n = 11) the mean values are: MNCV = 42.5 +/- 12.7; velocity change MNCV = 13.2 +/- 6.8; CMAP = 11 890 +/- 4750; dL = 2.97 +/- 0.57; for severe nerve compression (n = 23): MNCV = 40.6 +/- 11.0; change MNCV = 12.7 +/- 8.3; CMAP = 7948 +/- 5358; dL = 3.37 +/- 0.8. The difference for each parameter between the symptomatic and asymptomatic contralateral arm was statistically significant (p < 0.05) as it was for the difference of the parameters of the group with severe nerve compression in comparison to the asymptomatic arm. In the comparison of the moderate stage group with the asymptomatic arm there was only a significant difference for MNCV and there was no significant difference between the moderate and the severe group. In our study the calculated sensitivities for the electrodiagnostic studies were 76% for all symptomatic arms, 64% for the moderate group, and 83% for the severe nerve compression group. In all patients the MNCV was the most sensitive parameter.

Conclusion: Electrodiagnostic studies were only able to reveal 3/4 of all patients with an affection of the ulnar nerve and only 2/3 of the patients with a moderate stage of ulnar nerve compression. Although important for the further therapy, a differentiation between a moderate and severe degree of nerve compression was not possible.