Background
Clinical spectrum of immunoglobulin M (IgM) monoclonal gammopathy varies from IgM monoclonal gammopathy of unknown significance (IgM-MGUS) to hematological malignancies. We evaluated the clinical features, electrophysiological characteristics, and prognosis of patients with peripheral neuropathy associated with IgM monoclonal gammopathy (PN-IgM MG).
Methods
We retrospectively evaluated 25 patients with PN-IgM MG. Peripheral neuropathy was classified as axonal, demyelinating, or undetermined, based on electrophysiological studies. We classified the enrolled patients into the IgM-MGUS and malignancy groups, and compared the clinical and electrophysiological features between the groups.
Results
Fifteen patients had IgM-MGUS and 10 had hematologic malignancies (Waldenström’s macroglobulinemia: two and B-cell non-Hodgkin’s lymphoma: eight). In the electrophysiological evaluation, the nerve conduction study (NCS) criteria for demyelination were met in 86.7% of the IgM-MGUS group and 10.0% of the malignancy group. In particular, the distal latencies of the motor NCS in the IgM-MGUS group were significantly prolonged compared to those in the malignancy group (median, 9.1 ± 5.1 [IgM-MGUS], 4.2 ± 1.3 [malignancy], p = 0.003; ulnar, 5.4 ± 1.9 [IgM-MGUS], 2.9 ± 0.9 [malignancy], p = 0.001; fibular, 9.3 ± 5.1 [IgM-MGUS], 3.8 ± 0.3 [malignancy], p = 0.01; P-posterior tibial, 8.3 ± 5.4 [IgM-MGUS], 4.4 ± 1.0 [malignancy], p = 0.04). Overall treatment responses were significantly worse in the malignancy group than in the IgM-MGUS group (p = 0.004), and the modified Rankin Scale score at the last visit was higher in the malignancy group than in the IgM-MGUS group (2.0 ± 1.1 [IgM-MGUS], 4.2 ± 1.7 [malignancy], p = 0.001), although there was no significant difference at the initial assessment.
Conclusions
The risk of hematological malignancy should be carefully assessed in patients with PN-IgM MG without electrophysiological demyelination features.

Electrodiagnostic studies such as nerve conduction studies (NCS) and needle electromyography (EMG) provide important and complementary information for evaluating patients with suspected neuromuscular disorders. NCS and needle EMG are reasonably safe diagnostic investigations and are generally associated with only mild transient discomfort when performed by experienced physicians. However, there is the risk of complications in some patients, because NCS involve the administration of electric current and EMG involves inserting a needle percutaneously into muscle tissue. This article reviews the potential risks of NCS and needle EMG.

Citations

• Bioelectric medicine: unveiling the therapeutic potential of micro-current stimulation
  Hana Lee, Seungkwan Cho, Doyong Kim, Taehyun Lee, Han Sung Kim
  Biomedical Engineering Letters.2024; 14(3): 367.     CrossRef
• Needle electromyography does not meaningfully impact findings in MR‐neurography/−myography
  Stefan Sondermann, Tobias Boppel, Katharina Fieseler, Peter Schramm, Tobias Bäumer, Peter Trillenberg
  Muscle & Nerve.2024; 69(4): 409.     CrossRef

The measurement of nerve conduction is an expression of the pathophysiological state of the nerves and an essential tool for the study of various neuropathies. The clinical usefulness of nerve conduction studies(NCS) in the diagnosis of diffuse and focal neuropathies has been thoroughly validated. This article decribes the general guidelines for performing nerve conduction studies including H-reflex and F-wave. And the basic skills of NCS, the factors (physiological and nonphysioloigcal) affecting nerve conduction and clinical applications will be briefly discussed.

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.

Background
The most distal sensory fibers of the feet are often affected first in polyneuropathy. However, they are not evaluated in routine nerve conduction studies. Thus we evaluated the dorsal sural sensory nerve in patients with sensorimotor polyneuropathy with normal sural response, in order to assess the usefulness in electrodiagnostic practice.Methods: In this study, 53 healthy subjects and 27 patients with clinical evidence of sensorimotor polyneuropathy were included. In all subjects, peripheral motor and sensory nerve studies were performed on the upper and lower limbs including dorsal sural nerve conduction studies. On electrodiagnostic testing, all patients had normal sural responses.Results: The dorsal sural sensory nerve action potentials (SNAPs) mean amplitude was 13.12

Although various criteria on the diagnosis of diabetic neuropathy are applied from trial to trial, being tailored in concert with its purpose, the utmost evidences of the diagnosis are subjective symptoms and objective signs of neurologic deficit. The application and interpretation of auxiliary electrophysiological test including nerve conduction study (NCS) should be made on the context of clinical pictures. The evaluation of the functions of small, thinly myelinated or unmyelinated nerve fibers has been increasingly stressed recently with the advent of newer techniques, e.g., measurement of intraepidermal fiber density, quantitative sensory testing, and autonomic function test. And the studies with those techniques have shed light to the nature of the evolution of diabetic neuropathy. The practical application of these techniques to the diagnosis of diabetic neuropathy in the individual patients, however, should be made cautiously due to several shortcomings: limited accessibility, wide overlapping zone between norm and abnormality with resultant unsatisfactory sensitivity and specificity, difficulty in performing subsequent tests, unproven quantitative correlation with clinical deficit, and invasiveness of some technique. NCS, as an extension of clinical examination, is still the most reliable electrophysiological test in evaluating neuropathy and gives the invaluable information about the nature of neuropathy, whereas the newer techniques need more refinement of the procedure and interpretation, and the accumulation of large scaled data of application to be considered as established diagnostic tools of peripheral neuropathy.

Background
The medial plantar nerve (MPN) is a distal branch of the posterior tibial nerve, and various methods of nerveconduction study for MPN have been introduced so far. Hemmi et al described a new method (Hemmi's method) forrecording medial plantar sensory nerve action potentials (SNAPs), which is considered as a simple and reliable method formeasuring medial plantar SNAPs. This study was aimed to establish the normal values for the MPN conduction study amongKoreans and to compare the sensitivities of three different methods for MPN conduction study (Hemmi, Oh, and Saeed'smethod) in detecting evidence of peripheral neuropathy among diabetic patients. Methods: In 27 healthy subjects, MPN conductionstudy using Hemmi