Electrodiagnostic approach to the patient with suspected myopathy

Rapid identification of human muscle disease with fibre optic Raman spectroscopy

We demonstrate the use of fibre optic Raman spectroscopy for the rapid identification of muscle disorders.

Development and Preliminary Validation of an Electromyography-Scoring Protocol for the Assessment and Grading of Muscle Involvement in Patients With Juvenile Idiopathic Inflammatory Myopathies

INTRODUCTION

We performed a pilot study in order to investigate the feasibility of an electromyography (EMG)-scoring protocol for the assessment of disease activity in juvenile idiopathic inflammatory myopathies (JIIM).

METHODS

Children with JIIM followed up in a tertiary-level care center underwent standardized clinical, laboratory, and EMG assessment. An EMG-scoring protocol was devised by a consensus panel including a pediatric neurophysiologist and two pediatric rheumatologists, based on a combined score obtained as the sum of (1) the presence of denervation signs (fibrillation potentials) and (2) motor unit remodeling (mixed pattern of short- and long-duration motor unit action potentials). The EMG-scoring protocol was then validated following the Outcome Measures in Rheumatoid Arthritis Clinical Trials filter for outcome measures in rheumatology and the consensus-based standards for the selection of health measurement instruments methodology.

RESULTS

Thirteen children (77% females) were included in the study, with a median age of 10 years (interquartile range: 7-17 years) and median disease duration of 11.8 months (interquartile range: 2.1-44.5). A total of 39 EMG examinations were evaluated. A strong positive association between a standardized tool for muscle strength assessment and the combined score was observed. No significant associations were found with both creatine kinase and erythrocyte sedimentation rate levels.

DISCUSSION

Our EMG-scoring protocol is the first standardized and reproducible tool for the neurophysiologic evaluation and grading of muscle involvement in patients with JIIM and could provide relevant additional information in the assessment and follow-up of these rare conditions.

Electrodiagnostic Assessment of Myopathy

Electrodiagnostic testing is a useful tool in the evaluation of suspected myopathy and helps to confirm the presence of a myopathy and exclude disease mimickers. The electrodiagnostic pattern of findings during testing guides subsequent laboratory evaluation, genetic testing, and in identifying potential muscle biopsy targets. It also provides a baseline for subsequent assessment of disease progression or response to therapy. This article summarizes the approach to electrodiagnostic assessment in various myopathic disorders.

Subclinical myopathic changes in COVID-19

Introduction

Coronavirus disease 2019 (COVID-19) is associated to neuromuscular symptoms in up to 10.7% of hospitalized patients. Nevertheless, the extent of muscular involvement in infected subjects with no signs of myopathy has never been assessed with neurophysiological investigations.

Methods

Over a 3-week period — from April 30 through May 20, 2020 — a total of 70 patients were hospitalized in the Internal Medicine Ward of the Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico in Milan, Italy. After excluding patients who underwent invasive ventilation and steroid treatment, 12 patients were evaluated. Nerve conduction studies (NCS) included the analysis of conduction velocity, amplitude, and latency for bilateral motor tibial, ulnar nerves, and sensory sural and radial nerves. Unilateral concentric-needle electromyography (EMG) was performed evaluating at least 4 areas of 8 selected muscles. For each muscle, spontaneous activity at rest, morphology, and recruitment of motor unit action potentials (MUAPs) were evaluated.

Results

While nerve conduction studies were unremarkable, needle electromyography showed myopathic changes in 6 out of 12 subjects. All patients were asymptomatic for muscular involvement. Clinical features and laboratory findings did not show relevant differences between patients with and without myopathic changes.

Conclusion

Our data show that in SARS-CoV-2 infection muscular involvement can occur despite the absence of clinical signs or symptoms and should be considered part of the disease spectrum. The application of muscle biopsy to unravel the mechanisms of myofiber damage on tissue specimens could help to clarify the pathogenesis and the treatment response of coronavirus-mediated injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-021-05469-8.

The Diagnostic Yield of Electromyography at Detecting Abnormalities on Muscle Biopsy: A Single Center Experience

Historically, electromyography (EMG) is utilized early in the diagnostic evaluation of neuromuscular disorders, but its importance may be diminishing with more sophisticated genetic, imaging and immunohistochemistry investigations now available. In the present study, the diagnostic yield of EMG at predicting pathological abnormalities confirmed by muscle biopsy was determined at our neuroscience center. A retrospective study of consecutive cases reviewed at neuromuscular multidisciplinary meetings between 2007 and 2016 identified patients who had EMG and muscle biopsy as part of their diagnostic evaluation. EMG and biopsy findings were categorized as myopathic, neurogenic or normal. The diagnostic accuracy was determined by calculating the concordance between EMG and pathological findings. Of the 175 cases included in the analysis, there was definite concordance between EMG and muscle biopsy findings in 134 cases (76.6%). Abnormal EMG produced sensitivity of 87% and specificity of 65% for abnormal muscle biopsy. Seventeen patients had a normal EMG and an abnormal muscle biopsy, of which 6 had histopathological findings consistent with mitochondrial myopathy, central core myopathy or glycogen storage disorder. Conflicting EMG and muscle biopsy findings were observed in 10 cases. Inclusion body myositis, chronic neuromuscular disorders and dual pathologies were associated with discordant findings. This study demonstrates that EMG has accurate predictive value in diagnosing neuromuscular disorders at our neuroscience center. EMG retains a vital role, particularly in initial diagnostic evaluations of neuromuscular disorders.

Needle electromyography and histopathologic correlation in myopathies

INTRODUCTION

Needle electromyography (EMG) findings help confirm myopathy and may indicate specific pathologic changes on muscle biopsy.

METHODS

We conducted a retrospective chart review of 218 consecutive patients referred for muscle biopsy. Presence of specific needle EMG findings was correlated with pathologic findings of inflammation, necrosis, splitting, and vacuolar changes. Sensitivity, specificity, and positive and negative predictive values of specific EMG findings for pathologic changes were calculated.

RESULTS

Short-duration motor unit potentials (MUP) were sensitive (83%-94%) but not specific (34%-49%) for pathologic changes. Fibrillation potentials were 65%-74% sensitive and 58%-81% specific for inflammation, necrosis, splitting, or vacuolar changes. The absence of fibrillation potentials had high negative predictive value (82%-93%) for inflammation, splitting, or vacuolar changes.

DISCUSSION

Fibrillation potentials and short-duration MUPs predict pathologic changes of muscle fiber necrosis, splitting, and/or vacuolar changes (as seen with inflammatory myopathies and muscular dystrophies). Absence of fibrillation potentials suggests other myopathologic changes (e.g., congenital myopathy). Muscle Nerve 59:315-320, 2019.

A cola-induced hypokalemic rhabdomyolysis with electromyographic evaluation: A case report

OBJECTIVE

To report a rare case of hypokalemic rhabdomyolysis induced by the heavy and prolonged ingestion of cola-based beverages, and its uneventful recovery after kalemia normalization.

METHODS

We report a 38-year-old Caucasian male presented in our emergency room with a recent and progressive weakness of the lower limbs proximal muscles.

RESULTS

A dietary history revealed a prolonged ingestion of cola-based beverages. Blood tests showed severe hypokalemia and marked increase in serum creatine phosphokinase. The analysis of cerebrospinal fluid resulted normal. Electromyography was suggestive for a myopathy. The clinical, laboratory and neurophysiological data were evocative for a cola-induced hypokalemic rhabdomyolysis. After kalemia normalization, the improvements of the electromyographic findings paralleled the clinical recovery.

CONCLUSION

Chronic consumption of large amount of cola-based soft drinks may result in severe symptomatic hypokalemia, eventually leading in turn to myopathy. To our knowledge, this is the first description of the electromyographic findings of the cola-induced hypokalemic rhabdomyolysis. An early diagnosis and a prompt treatment appear to be crucial for a benign clinical course.

Proximal Limb Weakness in a Patient with Celiac Disease: Copper Deficiency, Gluten Sensitivity, or Both as the Underlying Cause?

Celiac disease has been associated with several neurologic disorders which may result from micronutrient deficiencies, coexisting autoimmune conditions, or gluten sensitivity. Copper deficiency can produce multiple neurologic manifestations. Myeloneuropathy is the most common neurologic syndrome and it is often irreversible, despite copper replacement. We report the case of a 55-year-old man who presented with progressive proximal limb weakness and weight loss in the setting of untreated celiac disease without gastrointestinal symptoms. He had anemia, neutropenia, and severe hypocupremia. The pattern of weakness raised the suspicion that there was an underlying myopathy, although this was not confirmed by electrodiagnostic studies. Weakness and hematologic abnormalities resolved completely within 1 month of total parenteral nutrition with copper supplementation and a gluten-free diet. Myopathy can rarely occur in patients with celiac disease, but the mechanism is unclear. Pure proximal limb weakness has not been previously reported in copper deficiency. We propose that this may represent a novel manifestation of hypocupremia and recommend considering copper deficiency and gluten sensitivity in patients presenting with proximal limb weakness.

Proximal myopathy: diagnostic approach and initial management

Proximal myopathy presents as symmetrical weakness of proximal upper and/or lower limbs. There is a broad range of underlying causes including drugs, alcohol, thyroid disease, osteomalacia, idiopathic inflammatory myopathies (IIM), hereditary myopathies, malignancy, infections and sarcoidosis. Clinical assessment should aim to distinguish proximal myopathy from other conditions that can present similarly, identify patients who need prompt attention, like those with cardiac, respiratory or pharyngeal muscle involvement, and determine underlying cause of myopathy. Initial evaluation should include simple tests, like creatine kinase, thyroid function and (25)OH vitamin D levels, but further evaluation including neurophysiological studies, muscle imaging and muscle biopsy should be considered for patients in whom no toxic, metabolic or endocrine cause is found, and in those with clinical features suggestive of inflammatory or hereditary myopathy. Additionally, screening for malignancy and testing for anti-Jo1 antibody is indicated for selected patients with IIM. Management depends on underlying cause, and includes measures, such as removal of offending agent, correction of endocrine or metabolic problem, corticosteroids and immunosuppressive therapy for IIM, and physical therapy, rehabilitation and genetic counselling for muscular dystrophies.