Some cases of myasthenia gravis (MG) with abnormal spontaneous activity (ASA) in needle electromyography (EMG) have been reported, but the associated clinical characteristics remain to be fully elucidated. We report the case of a 36-year-old male with MG in whom ASA was observed. This study highlights that ASA may appear in needle EMG in patients with severe MG who predominantly have bulbar and/or respiratory involvement. Care is needed because this often accompanies myopathic features and can be misdiagnosed as myopathy.

Background
The median-to-ulnar comparison test (MUCT), and increasingly, ultrasonography (US) are considered as complementary to and more sensitive than median nerve conduction study (NCS) in diagnosing carpal tunnel syndrome (CTS).
Methods
In consecutive patients with hand paresthesia compatible with CTS but with normal median NCS, we additionally performed the MUCT and analyzed whether it yielded better diagnostic sensitivity.
Results
In total, 163 hands of clinically diagnosed CTS patients were examined with routine NCS. The MUCT and US were performed in 81 hands and 31 hands, respectively. While median NCS was diagnostic in 85 (52.1%) hands, MUCT failed to demonstrate superior sensitivity over median NCS in the other hands and US revealed related abnormalities better than both routine NCS (p=0.006) and MUCT (p=0.002).
Conclusions
The MUCT offered no additional diagnostic benefit. On the other hand, sonographic examination had higher sensitivity for the diagnosis of CTS when applying several diagnostic criteria. Thus, US could be the screening test for diagnosing CTS prior to NCS with higher sensitivity than MUCT. However, further studies are needed to define the appropriate diagnostic criteria for US.

Clinical evaluations, nerve conduction studies, and electromyography play major complementary roles in electrophysiologic diagnoses. Electromyography can be used to assess pathologic changes and localize lesions occurring in locations ranging from motor units to anterior-horn cells. Successfully performing electromyography requires knowledge of the anatomy, physiology, and pathology of the peripheral nervous system as well as sufficient skill and interpretation ability. Electromyography techniques include acquiring data from visual/auditory signals and performing needle positioning, semiquantitation, and interpretation. Here we introduce the basic concepts of electromyography to guide clinicians in performing electromyography appropriately.

Citations

• Artificial intelligence for automatic classification of needle EMG signals: A scoping review
  S. de Jonge, W.V. Potters, C. Verhamme
  Clinical Neurophysiology.2024; 159: 41.     CrossRef
• Flexible Electrode by Hydrographic Printing for Surface Electromyography Monitoring
  Xiong Zeng, Ying Dong, Xiaohao Wang
  Materials.2020; 13(10): 2339.     CrossRef

Blepharospasm is the condition in which there is involuntary closing of the eyelids due to sustained, forced dystonic contraction of orbicularis oculi (OO) muscle. So called apraxia of lid opening (ALO) is another condition of involuntary eyelid closure which is suspected to be originated from the involuntary levator palpebrae (LP) inhibition. Clinically it is difficult to differentiate blepharospasm and ALO, and these two conditions are sometimes associated. This fact makes it difficult to predict and evaluate Botulinum A toxin injection treatment outcome. These disorders of involuntary eyelid closure are thought to have disturbed normal antagonistic activities of OO and LP, so electrophysiologic evaluation using synchronous EMG recording of LP and OO helps understanding the antagonistic activities of these two muscles and the origin of varying forms of eyelid movement disorders, and analysing the cause of unsatisfactory response to the Botulinum A toxin treatment.

Nerve compression of the suprascapular nerve by a suprascapular notch occasionally occurs, but comperssion by a ganglion is very rare. We had experienced a case of compression of the suprascapular nerve by ganglionic cyst at the suprascapular notch, which confirmed by electromyographic studies after the diagnosis was suspected. MRI scan showed multiobulated cyst at the right suprascapular notch. The patient was treated by excision of the ganglion and had excellent result.

Electrodiagnostic studies are valuable in confirming the diagnosis of a disorder of neuromuscular transmission. They are used to distinguish presynaptic and postsynaptic abnormalities. These studies provide an objective measure of the severity of the illness and may be useful in assessing the response to therapy. This article reviews the electrodiagnostic techniques that are commonly used today and highlights their specificity, sensitivity, and pitfalls. Repetitive nerve stimulation test (RNST) and single-fiber electromyography (SFEMG) are the most available electrophysiologic test in the diagnosis of neuromuscular junction disorders. RNS showing 10% decrement in amplitude from the first to fourth or fifth intravolley waveform while stimulating at 2~5 Hz is valid for the diagnosis of MG. The degree of increment needed for the diagnosis of LEMS is at least 25% but most accurate when greater than 100%. Abnormal jitter or impulse blocking are the appropriate criteria for diagnosis of NMJ disorders when using SFEMG. SFEMG is more sensitive than RNS for the diagnosis of disorders of neuromuscular transmission, especially in MG but may be less specific or may not be available.

Electrodiagnostic studies can be a valuable method in the diagnosis and follow-up study of various neuromuscular diseases. They must be used as an extension of the clinical evaluation, however, and not as routine tests. After the physician decides what kinds of pathophysiology could explain the patient? signs and symptoms, he or she is then in a position to request specific electromyography (EMG) studies to shed light on diseases that could affect the anterior horn cells, nerve roots, peripheral nerve, neuromuscular junctions, or muscles. Nerve conduction studies (NCS) assess peripheral motor and sensory functions by recording the evoked response to stimulation of peripheral nerves. Motor NCS require stimulation of a peripheral nerve while recording from a muscle innervated by that nerve. Sensory NCS are performed by stimulating a mixed nerve while recording from a cutaneous nerve or by stimulating a cutaneous nerve while recording from a mixed or cutaneous nerve. Motor and sensory NCS studies have been used clinically for many years to identify the location of peripheral nerve disease in single nerves and along the length of nerves and to differentiate these disorders from diseases of muscle or the neuromuscular junction. NCS also can help to distinguish between axonal degeneration, segmental demyelination, and abnormal nerve irritability. But it is important to recognize the inherent limitations of the EMG study. First, the kinds of tests and the muscles or nerves to be tested must be determined by clinical findings. Then, the EMG findings must be interpreted in light of the clinical findings because no EMG results are pathognomonic of a specific disease entity. For these reasons, it is essential that the clinical problem be assessed throughly and that a careful neurological examination be performed before the electrophysiologic study.

The effect of serratus anterior dysfunction is seen in the scapular winging. We report 2 cases with winging scapula clinically but do not reveal denervation potentials in needle electromyography. Surface myoelectric measurements of median frequency and root mean square values show difference in fatigability and amplitude in affected side.

Sporadic inclusion body myositis (s-IBM) is an aquired slowly progressive inflammatory myopathy with unknown etiology. Although light microscopic abnormalities and characteristic histopathology on muscle biopsy distinguishes from other inflammatory myopathies, vacuolated muscle fibers, intracellular amyloid deposits or tubulofilaments in electromicroscopic findings are not definite in some patients. This review shows the prominently involved muscles in s-IBM and specific or nonspecific electrophysiologic manifestations from reported data for helping the diagnosis of definite-or probable-IBM patients. In lower limbs, the quadriceps is predominantly involved, as is iliopsoas, and tibialis anterior is common. In the upper limbs, the greatest weakness is in forearm finger flexors. Finger extensors, biceps and triceps also are moderately to prominently involved. The majority of patients demonstrate polyphasic MUAPs that are short in duration. An additional striking feature is the concomitant documentation of long-duration, large-amplitude, polyphasic MUAPs. In spite of the frequent mixed myopathic-neurogenic electromyographic findings of IBM, just like that of chronic myositis, asymmetric, slowly progressive weakness of flexor digitorum profundus or quadriceps femoris muscles after age of 50 is very necessary condition for the diagnosis of IBM.

Pneumothorax after needle electromyography is a rare complication, which usually associated with examination of diaphragmatic and intercostal muscles. However, by the literatures, it can also occur with supraspinatus, serratus anterior and paraspinal muscles. We experienced a case of pneumothorax after cervical paraspinal muscle needle electromyography. From the anatomical vulnerability of pneumothorax during needle insertion, we emphasized the importance of avoiding this complication.

Among the various physiological factors that affect nerve conduction velocity (NCV), temperature is the most important. Because the influence of temperature is the most important source of error. It is known from animal experiments that conduction is eventually completely blocked at low temperatures, the myelinated A fibers being the first affected and the thin fibers of group C the last. Many studies showed that the NCV decreases linearly with lowering temperature within the physiological range. The distal motor latency increased by 0.2 msec/

Intraoperative neuromonitoring (INM) is well known to be useful method to reduce intraoperative complications during the surgery of nervous system lesions. Evoked potentials are most commonly used among the electrophysiological tests. Brainstem auditory evoked potentials are for detecting the problems along the auditory pathways including the eighth cranial nerve and brainstem. Somatosensory evoked potentials are applied for preventing the spinal cord lesions. The INM is affected by many factors. In order to perform an optimal INM, the confounding factors including technical, anesthetical, and individual factors should be kept well under control. INM has frequent electrophysiologic changes during the surgery and it might be helpful to keep one

We report a patient with amyotrophic lateral sclerosis (ALS) who developed a pneumothorax after needle electromyography (EMG), probably of the intercostal muscles. Needle EMG on intercostal muscles has a high risk of pneumothorax, not only because electromyographers are unfamiliar to its technique, but also due to its close anatomical location to the pleural cavity. In our patient, advanced intercostal muscle atrophy due to disease process would have increased the risk further.