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Multifocal pyomyositis is a rare inflammatory myopathy caused by bacterial infection and abscess formation in multiple skeletal muscles. To date, electromyography (EMG) of pyomyositis has not been reported.We describe the EMG findings of a patient with pathologically proven multifocal pyomyositis.Muscles affected by pyomyositis demonstrate EMG features similar to those of other inflammatory myopathies. Other features such as acute entrapment neuropathy may exist concomitantly due to nerve compression from muscle abscess formation.

In ulnar neuropathy at the elbow (UNE), we determined how electrodiagnostic cutoffs [across-elbow ulnar motor conduction velocity slowing (AECV-slowing), drop in across-elbow vs. forearm CV (AECV-drop)] depend on pretest probability (PreTP).Fifty clinically defined UNE patients and 50 controls underwent ulnar conduction testing recording abductor digiti minimi (ADM) and first dorsal interosseous (FDI), stimulating wrist, below-elbow, and 6-, 8-, and 10-cm more proximally. For various PreTPs of UNE, the cutoffs required to confirm UNE (defined as posttest probability = 95%) were determined with receiver operator characteristic (ROC) curves and Bayes Theorem.On ROC and Bayesian analyses, the ADM 10-cm montage was optimal. For PreTP = 0.25, the confirmatory cutoffs were23 m/s (AECV-drop), and38 m/s (AECV-slowing); for PreTP = 0.75, they were much less conservative:14 m/s, and47 m/s, respectively.(1) In UNE, electrodiagnostic cutoffs are critically dependent on PreTP; rigid cutoffs are problematic. (2) AE distances should be standardized and at least 10 cm.

Electrodiagnostic procedures are routinely performed in patients with a variety of neuromuscular disorders. These studies are generally well tolerated and rarely thought to be associated with any significant side effects. However, needle electromyography is an invasive procedure and under certain situations has the potential to be associated with iatrogenic complications, including bleeding, infection, nerve injury, pneumothorax, and other local trauma. Similar complications are possible if needles are used for either stimulating or recording. In addition, like all other electrical devices and monitoring equipment connected to patients, electrodiagnostic testing carries the risk of stray leakage currents that under certain circumstances can result in electrical injury, especially in patients in the intensive care setting. Similarly, certain precautions are required during nerve conduction studies (NCS) in patients with pacemakers and other similar cardiac devices. In this review, we address the known and theoretical complications of NCS and needle electrode examination, and the possible methods to avoid such hazards.

Patients with severe carpal tunnel syndrome (CTS) may occasionally have absent median motor and sensory responses; in these cases, it is not possible to accurately localize the median mononeuropathy to the wrist using standard electrodiagnostic tests. We prospectively investigated the use of comparing the median motor latency to the second lumbrical and the ulnar motor latency to the interossei muscles in 28 patient hands with severe CTS and absent median motor and sensory responses. We found a prolonged latency difference in 92.8%. Along with its use in mild CTS, study of the lumbrical-interossei latency difference is helpful in patients with severe CTS with absent median motor and sensory responses.

Electrodiagnosis of carpal tunnel syndrome (CTS) often depends on the demonstration of focal slowing of median sensory fibers across the wrist. We compared the relative sensitivity of the four median innervated digits in demonstrating focal slowing in patients with CTS. Antidromic sensory studies of digits 1, 2, 3, and 4 were performed on 30 control subjects to develop normative data. Fifty-nine consecutive patients with CTS were then studied to determine the sensitivity of focal slowing of each median innervated digit. In the 26 CTS patients with a normal distal motor latency (DML) to abductor pollicis brevis, digit 1 was abnormal in 81%, digit 2 in 42%, digit 3 in 54%, and digit 4 in 38%. In the 33 CTS patients with a prolonged DML, digit 1 was abnormal in 94%, digit 2 in 88%, digit 3 in 91%, and digit 4 in 88%. We conclude that in milder cases of CTS with a normal DML, digit 1 is the most sensitive in identifying focal slowing of sensory conduction across the wrist. However, in patients with a prolonged DML, the sensitivity of sensory conduction is not significantly different among the four digits. © John Wiley & Sons, Inc.

The relative sensitivities of sensory, mixed nerve, and motor conduction studies in assessing ulnar neuropathy at the elbow have not yet been established. Using surface electrodes, we performed conduction studies across the elbow segment in 43 patients with symptoms referable to the ulnar nerve and 40 control subjects. Segmental slowing of motor conduction localized the lesion to the elbow in 14 of 21 patients (67%) with clear evidence of ulnar neuropathy on physical examination but only in 2 of 22 (9%) with subtle or no physical examination abnormalities. The diagnostic yield was increased by the finding of segmental slowing of sensory or mixed nerve conduction across the elbow to 86% and 68%, respectively, for each of the groups. We conclude that surface-recorded sensory and mixed nerve conduction studies appear to be more sensitive than motor studies in the electrodiagnosis of ulnar neuropathy at the elbow and are especially valuable in patients with subtle clinical involvement.