Neuromuscular Disease and Electrodiagnosis
Recognizing the pattern
Proximal weakness with Gowers sign, calf pseudohypertrophy, and markedly elevated creatine kinase suggests dystrophinopathy; genetic testing, not electrodiagnosis, confirms it. Floppy infants with preserved cognition, tongue fasciculations, and a deletion of SMN1 have spinal muscular atrophy. Charcot-Marie-Tooth presents with pes cavus, hammer toes, and absent reflexes. Juvenile myasthenia gravis shows fatigable weakness, ptosis, and a decremental response on repetitive stimulation. Acute symmetric ascending weakness with areflexia suggests Guillain-Barre syndrome, with cerebrospinal fluid albuminocytologic dissociation after the first week.
Electrodiagnosis in children
Myelin matures postnatally: conduction velocity is roughly 20 to 25 m/s in preterm infants, about 30 m/s at term, and reaches adult values (50 to 55 m/s) by 3 to 5 years. Distal latencies are longer and amplitudes smaller in neonates. Use age-matched normative values, keep limb temperature warm, and calculate distances carefully on short limbs. Needle examination with a concentric needle is brief and targeted; sedation carries respiratory risk, particularly in weak infants, so coordinate with anesthesia and have monitoring available.
Disease-specific management
Duchenne: corticosteroids prolong ambulation, so monitor weight, behavior, bone health, and cardiomyopathy with regular echocardiography; noninvasive ventilation and assisted cough support the restrictive respiratory decline; scoliosis surgery is considered when curves progress despite bracing. SMA: disease-modifying therapies have changed natural history, so rehabilitation goals shift toward standing, powered mobility, and contracture prevention.
Worked rule of thumb
In a floppy infant with a very high CK, skip the needle and order dystrophin genetics - electrodiagnosis adds risk and little information when a genetic diagnosis is available.