Perioperative Ulnar Neuropathy: Fact or Fiction?

Abstract & Commentary

Source: Stewart JD, Shantz SH. Perioperative ulnar neuropathies: A medicolegal review. Can J Neurol Sci. 2003;30:15-19.

Consider this all-too-familiar scenario. Patient X awakens from otherwise uneventful abdominal surgery and complains of ulnar nerve distribution weakness or tingling, or both. Ulnar neuropathy at the elbow (UNE) is documented, litigation ensues, and large sums of money exchange hands. Who is guilty and of what?

In a thoughtful and thorough review of the medico-legal literature, Stewart and associates highlight several important facts, often overlooked, concerning the above hypothetical. First and foremost, despite widespread adherence to decades-old wisdom and recommendations for preoperative positioning intended to prevent UNE, its incidence has not declined, suggesting that prepositioning does not protect the ulnar nerve. Secondly, among 22 peri-operative UNE patients, only 5 were aware of their symptoms on waking from anesthesia, with another 3 noting the problem on postoperative day 1.1 Most noted the onset during the first week (n = 10) or 2-4 weeks later (n = 4). Retrospective analysis of surgical cases at the Mayo Clinic (n = > 1.1 million) found UNE in 414 patients (0.04%) with most symptoms beginning > 24 hours post-operatively.2 Persistent UNE was seen mostly in men (70%), with other risk factors being diabetes, older age, > 2 weeks of hospitalization, and either a very thin or obese body habitus. Strikingly, neither duration of surgery or anesthesia nor patient position was associated with UNE. Complete recovery was seen in 53% by 1 year. In a prospective follow-up study,3 Warner et al studied 1502 adult surgical patients, excluding those with prior history of UNE or those undergoing cardiac surgery, the latter to prevent confusion with brachial plexopathy, a known complication of cardiac surgery. Only 7 (0.5%) developed UNE, and male gender was found to be the only risk factor. None experienced symptoms prior to postoperative day 2, and all began during the first week. Six were mild and purely sensory. Significantly, all had been padded for prevention of UNE. These findings indicate that peri-operative UNE may be postoperative in nature and related to convalescing in the recumbent position with leaning on the elbows. This possibility was underscored when Warner et al similarly found 2 UNE among 990 nonsurgical hospitalized medical patients.4 And do not presume that postoperative patients are sedated and thus unable to report UNE early on. Among 991 patients with postsurgical lower limb neuropathy, symptoms were reported within 4 hours of completing anesthesia,5 indicating that the late(r) reporting of UNE is due not to surgery but to its onset and causation during the recovery period. Judges should throw out lawsuits brought against surgeons for a presumed intraoperative UNE complication.

Commentary

Electrodiagnosis of UNE may itself be a challenging exercise. Guidelines were recently developed by the Quality Assurance Committee of the American Academy of Electrodiagnostic Medicine and the Quality Standards Subcommittee of the American Academy of Neurology (AAN) and endorsed by the AAN and the American Academy of Physical Medicine and Rehabilitation, to address this issue.6 These included:

Electrodiagnosis of UNE may be made on the basis of one or more of the following:

1. Slowed conduction velocity across the elbow to below 50 m/s;

2. Slowed conduction velocity across the elbow by more than 10 m/s compared to the below elbow segment;

3. A > 20% drop in compound muscle action potential (CMAP) amplitude across the elbow (remember to exclude a Martin-Gruber anastomosis); or

4. A significant change in CMAP configuration across the elbow (but note that significant is not defined).

When the diagnosis remains uncertain:

1. Record from the first dorsal interosseous (FDI) muscle;

2. Use the inching technique to look for latency, CMAP amplitude, and configuration changes;

3. Compare conduction velocity across the elbow to that between axilla and elbow; and

4. When desperate, try recording from forearm ulnar muscles.

Remember to use needle electromyography, if warranted, to exclude a more widespread, or second, lesion.— Michael Rubin

Dr. Rubin is Professor of Clinical Neurology, New York Presbyterian Hospital-Cornell Campus

References

1. Kroll DA, et al. Anesthesiology. 1990;73:202-207.

2. Warner MA, et al. Anesthesiology. 1994;81:1332-1340.

3. Warner MA, et al. Anesthesiology. 1999;90:54-59.

4. Warner MA, et al. Anesthesiology. 2000;92:613-615.

5. Warner MA, et al. Anesthesiology. 2000;93:938-942.

6. Neurology. 1999;52:688-690.