Diagnostic Yield Of Pediatric EMG In Myopathic Disorders (P4.322)

Background: Electromyography (EMG) interpretation of myopathic disorders is technically challenging in children, particularly smaller children. In this study we compared EMG to the muscle biopsy which is considered to be the gold standard for the diagnosis of myopathy. Methods: Retrospective chart review of patients <18 years, who underwent EMG at the electrophysiology laboratory of the Mayo Clinic, Rochester, MN over 5 years (2009-2013). EMG was performed under conscious sedation in most of the children. Nerve conduction studies were performed in at least 2 nerves (one motor and sensory) and EMG performed in at least 2 muscles in ipsilateral upper and lower limb. 224 patients with the following the referral diagnoses (myopathy, muscle weakness, neuromuscular disorders, myositis, myalgia, myoglobinuria, myasthenia, myotonia, cramps, periodic paralysis, hypotonia, and developmental delay) were reviewed for myopathic EMG. We included children who had an EMG and a muscle biopsy performed for further analysis. Muscle biopsies were evaluated at our muscle laboratory. Myopathic EMG was defined as short duration, low amplitude motor unit potentials with rapid recruitment. Myopathic biopsy was defined as increased internal nuclei, fiber size variation, necrotic or regenerating fibers, or structural changes within the muscle fibers. Results: 75 cases were included, age range (4 months to <18 years). The following observations were made: EMG myopathic and muscle biopsy confirmed myopathy - 33, EMG myopathic and muscle biopsy normal -7; EMG normal and muscle biopsy myopathic - 4 (all had metabolic myopathy) and lastly EMG and biopsy both normal - 31. Fibrillation potentials were mainly identified in cases of inflammatory myopathy. Myotonic discharges were noted in a case of congenital myopathy with fiber type disproportion. Conclusions: Pediatric EMG is 89% sensitive (33/37) and 82% specific (31/38)when performed in a controlled environment under conscious sedation for detecting myopathic disorders. EMG can be normal in metabolic myopathies and further work-up should be considered if the clinical suspicion is strong.