Nonhomogeneous volume conduction effects affecting needle electromyography: an analytical and simulation study

Objective: Needle electromyography (EMG) is used to study the electrical behavior of myofiber properties in patients with neuromuscular disorders. However, due to the complexity of electrical potential spatial propagation in nonhomogeneous diseased muscle, a comprehensive understanding of volume conduction effects remains elusive. Here, we develop a framework to study the conduction effect of extracellular abnormalities {and electrode positioning} on extracellular local field potential (LFP) recordings. Methods: The framework describes the macroscopic conduction of electrical potential in an isotropic, nonhomogeneous (i.e., two tissue) model. Numerical and finite element model simulations are provided to study the conduction effect in prototypical monopolar EMG measurements. Results: LFPs recorded are influenced in amplitude, phase and duration by the electrode position in regards to the vicinity of tissue with different electrical properties. Conclusion: The framework reveals the influence of multiple mechanisms affecting LFPs including changes in the distance between the source -- electrode and tissue electrical properties. Clinical significance: Our modeled predictions may lead to new ways for interpreting volume conduction effects on recorded EMG activity, for example in neuromuscular diseases that cause structural and compositional changes in muscle tissue. These change will manifest itself by changing the electric properties of the conductor media and will impact recorded potentials in the area of affected tissue.

Treatment of progressive paralysis associated with cervical myelopathy and suspected amyotrophic lateral sclerosis: A case report

Background: Amyotrophic lateral sclerosis (ALS) is an intractable progressive disease, with an incidence of 2.2– 2.3 per 100,000 individuals, which is not extremely low. ALS symptoms are accompanied by spinal myeloradicular motor deficit; its differential diagnosis is must because progressive paralysis needs emergency surgery. Case Description: A 64-year-old man with suspected ALS showing progressive paralysis with cervical myelopathy was diagnosed as normal after performing a nerve conduction study preoperatively. Postoperative diffuse fasciculation after posterior decompression allowed the diagnosis of ALS through needle electromyography (EMG). Thereafter, the patient’s condition slowly deteriorated and he died after 16 months. Conclusion: Surgery might aggravate ALS symptoms; however, surgery for progressive paralysis in patients with suspected ALS is required for distinguishing patients with non-ALS paralysis. Approximately 70% of cases have spinal-onset ALS lacking typical cranial nerve symptoms; thus, to prevent unnecessary surgery, surgeons should at least know the characteristic features of ALS and should be aware that early diagnosis requires needle EMG for definitive diagnosis of ALS.

Nerve Conduction Studies and Needle Electromyography

Nerve conduction studies (NCSs) and needle electromyography (EMG) should be considered extensions of the neurologic history and examination of the peripheral sensory and motor systems. NCSs assess large, myelinated sensory and motor nerve fibers. EMG assesses primarily type 1 muscle fibers. Because of the limitations of NCSs and EMG, small-fiber function (ie, small-fiber neuropathies) and, to an extent, type 2 muscle-fiber diseases (ie, steroid myopathy) cannot be excluded with these studies. The main goal of NCSs and EMG is to obtain objective evidence of disease within the peripheral nervous system and to assist with localization of the problem.

Posterior interosseous neuropathy: distinguishing from a proximal radial neuropathy

The posterior interosseous nerve is the terminal motor branch of the radial nerve that innervates the extensor carpi ulnaris and the extensors of the thumb and fingers. We describe a case of a posterior interosseous neuropathy presenting with the typical ‘finger drop’ and partial ‘wrist drop’. We focus on the clinical signs that distinguish it from a more proximal radial neuropathy, clarified by nerve conduction studies and needle electromyography. Multimodal imaging of the forearm did not identify a compressive lesion. Persistent symptoms prompted surgical exploration 5 years after initial onset. It identified compression of the posterior interosseous nerve in the region of the arcade of Frohse and leash of Henry. The sites were decompressed and concurrent salvage secondary reconstructive tendon transfers were required in view of the severe axonal loss with minimal chance of functional reinnervation.

Radiation-Induced Myopathy Developing in a Hodgkin Lymphoma Patient: An Autopsy Case with Systemic Muscle Sampling

Radiation-induced myopathy (RIM) is a rare complication occurring years after radiotherapy. RIM basically occurs within the irradiation field, but some cases have been reported to be accommodated by myopathy outside the irradiation field, and the actual extent of RIM is obscure. The presented case also showed decreased MMT scores and abnormal needle electromyography results in the muscles outside the irradiated field, and the patient was initially thought to have RIM both within and outside the irradiated field. However, while systemic postmortem muscle sampling revealed prominent myopathy in line with RIM in the irradiated muscles, only mild myogenic changes that could be explained by other causes such as age-related sarcopenia, radiculopathy, and disuse atrophy were observed in the non-irradiated muscles. The number of biopsy sites in live patients is limited due to the invasive nature of the procedure, but we were privileged to systemically evaluate the extent of myopathy through multiple muscle sampling including muscles both inside and outside of the irradiation field because this was an autopsy case. Through the presented case, we conclude that RIM is a phenomenon most probably limited to the muscles within the irradiated field, and myopathy outside the irradiation is due to other causes.