LIMITATIONS
• EMG can assess nerve and muscle function, but
can rarely lead to a specific etiologic diagnosis (e.g., a radiculopathy from a
disk herniation will appear similar to one caused by a tumor)
• Many of the abnormalities on nerve conductions
and needle EMG are time dependent. In general, most nerve conduction
abnormalities require a week to develop; many of the abnormalities on needle EMG
requires several weeks. Thus, EMG studies may be insensitive if the disorder is
too acute.
• Routine studies are available for many but not
all peripheral nerves. Some nerves are not possible to study with routine EMG
studies.
• A minority of patients are electrically
sensitive and may have difficulty with the nerve conduction studies.
• A minority of patients are intolerant of the
needle examination and may have difficulty completing the study.
• Much of the study, especially the needle EMG,
requires patient cooperation. Thus, the study is limited in young children, and
in cognitively impaired adults.
• The study is individualized for the patient.
Likewise, abnormalities must be determined on-line in real time as the study
proceeds. The value of the information is highly dependent on the skill and
ability of the EMG physician performing the examination.
CONTRAINDICATIONS AND RISKS
EMG studies are generally well tolerated and rarely thought to be associated
with any significant side effects, other than mild discomfort at the time of the
procedure and possibly minor bruising as a consequence of the needle EMG.
However, the needle EMG is an invasive procedure and under certain situations
has the potential to be associated with complications, including bleeding,
infection, nerve injury, pneumothorax and other local trauma. In addition, like
all other electrical devices and monitoring equipment connected to patients,
nerve conduction studies and needle EMG carry the risk of stray leakage currents
that under certain circumstances can result in electrical injury.
Relative contraindications include:
• Coagulopathy.
Patients on anticoagulation or who have marked thrombocytopenia are at higher
risk for bleeding following needle EMG. In these patients, needle EMG needs to
be limited to a few superficial muscles.
• Electrically Sensitive
Patients. The electrical impulses delivered during routine nerve
conduction studies are safe and well tolerated. However, very small currents
applied to the heart may result in arrhythmia and death. The skin forms a high
resistance barrier protecting the heart from superficial electrical currents. In
patients with central catheters and external pacer wires, the heart is at
greater risk for stray currents reaching the heart. These patients are known as
"electrically sensitive". Electrical stimulation during nerve conduction studies
near these sites is contraindicated. Likewise, patients with pacemakers and
other cardiac devices should not have nerve conductions performed near these
devices.
• Risk of Pneumothorax.
Although very rare, pneumothorax has been reported following needle EMG of
several proximal chest muscles. Among are the serratus anterior, supraspinatus,
rhomboids and lower cervical/thoracic paraspinal muscles. |