Muscle disorders: the latest investigations

Abstract

Patients with muscle disorders can present a diagnostic challenge to physicians because of the different ways they can present and the large number of different underlying causes. Recognition of the 'myopathic phenotype' coupled with investigations usually including electrodiagnostic and histological investigations have been essential for diagnosing the underlying cause of a myopathy. Despite these standard investigations, some patients can remain undiagnosed. New tests including more specific antibody tests for immune-mediated myopathies and the introduction of next-generation sequencing promise to revolutionise diagnostic approaches for immune and inherited myopathies, but clinical expertise remains essential to choose the most appropriate tests and interpret the results. The aim of this review is to provide an overview of the different presentations to the neuromuscular clinic and the latest investigations that can be helpful in the diagnosis of muscle disorders.

Molecular diagnosis of muscular diseases in outpatient clinics

“…Indeed, it is particularly invasive, and specific antibodies are not available for all proteins encoded by causal genes. 1 Therefore, genetic testing is increasingly used and can be obtained in a noninvasive manner. Across different countries such as Canada, the United States, China, Korea, Germany, the United Kingdom, Egypt, Poland, Australia, and Japan, gene panel sequencing has a yield varying from 16% to 65%, [2][3][4][5][6][7] depending on subgroups of patients' selection, whereas exome sequencing has a yield in between 13% and 69% [8][9][10][11][12][13][14][15] in different settings.…”

Diagnostic Approach to Proximal Myopathy

“…9.4). When the cause of muscle weakness is unclear, appropriate testing should be performed, and it is recommended to start with blood tests including electrolytes (potassium, calcium, phosphate, and magnesium), thyroid-stimulating hormone (TSH) level, alkaline phosphatase and 25 (OH) vitamin D level, and HIV [16].…”

“…However, it is neither specific nor sensitive as troponins [18]. CK might be falsely elevated secondary to ethnicity (can be high in Afro-Caribbean men), exercise (can remain elevated for up to 72 h), intramuscular injections, needle electromyography (EMG), medications, hypothyroidism, and motor neuron disease [16].…”

“…Normal EMG examination, however, would not exclude myopathy [18]. In case of polymyositis, the site of muscle biopsy should be opposite to where the EMG was conducted [16].…”

Peripheral Neuropathy Presenting as Myopathy That was Confused With Inflammatory Myositis

“…1 Electrodiagnostic studies such as needle electromyography (EMG), nerve conduction studies (NCS), and muscle biopsies are needed to confirm the diagnosis. 2,3 A 34-year-old female patient presented with sudden weakness and painful swelling of the left lower extremity. She had also developed multiple bullae that progressed to diffuse swelling ( Figure 1a).…”