Diaphragm Electromyography (EMG) is a diagnostic test that assesses the electrical activity of the diaphragm, the primary muscle for breathing. It helps healthcare professionals understand how well the diaphragm functions by measuring its electrical signals. This provides insights into the health of the diaphragm and the nerves that control it.
What Diaphragm EMG Measures
The test measures the electrical signals produced by the diaphragm, including action potentials, which are impulses that cause muscle contraction. This helps evaluate the strength and timing of the diaphragm’s activation.
A doctor may recommend a Diaphragm EMG for unexplained shortness of breath, especially when lying down, or if diaphragm weakness or paralysis is suspected. The test also helps diagnose neuromuscular disorders affecting breathing. The phrenic nerve provides the primary motor supply to the diaphragm, and EMG can assess the integrity of its signals.
How Diaphragm EMG is Performed
Diaphragm EMG uses different methods to record the muscle’s electrical activity. One common approach is needle EMG, where small, thin needles are inserted directly into the diaphragm. Ultrasound guidance is often used for accurate placement and to reduce complications.
An alternative method is esophageal EMG, which involves passing a catheter with electrodes down the esophagus. These electrodes are positioned near the diaphragm to record its electrical activity. This method provides a reliable signal and is useful for assessing neural respiratory drive.
Surface EMG, using electrodes on the chest wall skin, is less common for direct diaphragm assessment. Signals from the diaphragm can be contaminated by surrounding chest wall muscles, making clear readings difficult. Patients may experience mild discomfort during needle insertion, or a sensation of a tube in the throat with the esophageal method. The test duration is usually brief, often taking only a few minutes.
What Diaphragm EMG Can Reveal
Diaphragm EMG reveals abnormal electrical patterns or a lack of activity in the diaphragm, indicating various respiratory problems. The test helps distinguish between muscle problems (myopathy) and nerve problems (neuropathy) impacting the diaphragm.
The results can specifically point to diaphragm weakness or paralysis, whether affecting one side (unilateral) or both sides (bilateral). Diaphragm EMG is used in diagnosing neuromuscular disorders such as Amyotrophic Lateral Sclerosis (ALS), muscular dystrophy, myasthenia gravis, and critical illness neuropathy, where respiratory muscle involvement is a concern. For instance, in ALS patients, abnormal diaphragm EMG findings can indicate sub-clinical respiratory muscle dysfunction even before symptoms are obvious. The procedure also helps assess the recovery of diaphragm function in conditions like myasthenia gravis and critical illness, providing insights into a patient’s readiness for weaning from mechanical ventilation.