Electromyography
Definition: Electromyography (EMG) is a neurophysiological method used to assess the function of muscles and peripheral nerves by recording their electrical activity.
It helps differentiate: Neuropathic disorders. Myopathic disorders. Neuromuscular junction disorders
Types
1. Needle EMG
- Needle electrode inserted into muscle
- Records muscle electrical activity at rest and during contraction
2. Nerve Conduction Studies (NCS)
- Peripheral nerve is electrically stimulated
- Measures conduction velocity and response amplitude
Normal EMG
- At Rest: Electrical silence
- During Contraction: Motor unit action potentials (MUAPs). Increasing activity with stronger contraction
Abnormal Findings
1.Neurogenic (Neuropathic) Lesions
- Examples: Peripheral neuropathy. Radiculopathy. Motor neuron disease
- EMG Findings: Fibrillation potentials. Fasciculations. Large, long-duration MUAPs. Reduced recruitment
2.Myopathic Lesions
- Examples: Muscular dystrophy. Inflammatory myopathies
- EMG Findings: Small, short-duration MUAPs. Early recruitment
3.Neuromuscular Junction Disorders
- Example: Myasthenia Gravis
- Finding: Decremental response on repetitive nerve stimulation
Clinical Indications: Peripheral neuropathies. Radiculopathies. Plexopathies. Motor neuron diseases. Myopathies. Neuromuscular junction disorders. Entrapment neuropathies (e.g., carpal tunnel syndrome)
Nerve Conduction Studies
- Parameters Measured: Conduction velocity. Latency. Amplitude
- Demyelinating Neuropathy: Markedly slowed conduction velocity
- Axonal Neuropathy: Reduced amplitude