During the past 10-15 years the use of ultrasound (US) in the diagnosis of neuromuscular disorders has significantly accelerated. Traditional Electrodiagnostic Tests (EDX) provide insight into the location and pathophysiology of neuromuscular disorders. However, EDX may not provide clues to the underlying structural cause, which is more readily uncovered by imaging studies like ultrasound and MR neurography. The advantages of US are low cost, being painless and readily available at the point of care. There have been suggestions that US can replace EDX in some situations like confirming clinical diagnosis of carpal tunnel syndrome . However, currently available US technology cannot provide adequate information regarding the underlying pathophysiology: demyelination, axon loss or both. EDX and US complement each other effectively in providing comprehensive data to respond to the practical question is the problem surgical or non-surgical.
While it is desirable to do US in every patient undergoing EDX, in a busy clinical EDX facility, the amount of time the electromyographer can devote to any given patient is not unlimited; hence it may not be feasible to do US in every patient undergoing EDX. This brings up the question as to how to identify situations where EDX has to be complemented with US. We have been developing guidelines in our facility reflecting where US
plays a crucial role in providing valuable information for diagnosis and management. We will not be discussing the role of US in nerve block, locating nerve/muscle for biopsy, and therapeutic procedures like botulinum toxin injections in this review, but concentrate upon the role of US in complementing EDX for more precise diagnosis.
Significant axon loss leading to absent Compound Muscle Action Potentials (CMAP) and Sensory Nerve Action Potentials (SNAP) Typical examples are severe entrapment of median nerve at the carpal tunnel and ulnar nerve at the elbow. Documentation of increased Cross-Sectional Area (CSA) of median nerve at the carpal tunnel inlet/outlet and normal CSA at the forearm serve as reliable criteria to localize median neuropathy to the carpal tunnel . A typical feature is the hour glass appearance in long axis views (Figure 1). Similarly, severe ulnar neuropathies at the elbow or wrist  can be confirmed by documentation of increased CSA proximal to the site of entrapment (Figure 2). Patients with severe fibular neuropathy causing loss of CMAP of Extensor Digitorum Brevis (EDB) and tibialis anterior / peroneus longus pose a similar challenge and US may provide the answer (Figure 3).
b. In cases of longstanding entrapment, in addition to
focal demyelination, there may be retrograde  and anterograde
demyelination leading to diffuse slowing of conduction; precise
localization may not be possible in such cases with EDX alone.
US is of great value in these situations by providing accurate
c. In cases of demyelinating polyneuropathy with diffuse
slowing of nerve conduction, confirming additional presence of
entrapment can be challenging. In this context, US showing findings
typical of entrapment can be helpful. Most common situation
is patients with diabetic polyneuropathy in whom additional
presence of carpal/cubital tunnel syndrome is suspected.
a. Patients with symptoms of carpal tunnel syndrome
rarely show normal nerve conduction studies. There are a number
of publications which suggest that high frequency ultrasonography
may show abnormalities in such patients [5,6].
b. US has also been reported to be positive in patients with
ulnar neuropathy at the elbow, when EDX is negative .
Distinction between axonotmesis and neurotmesis is a crucial
piece of information for planning the ideal time for surgical
intervention; if neurotmesis can be confirmed, early surgical
intervention is indicated. US can provide such information by
revealing area of discontinuity of the nerve in neurotmesis (Figure
This is highly important for prompt initiation of treatment
with intravenous immunoglobulin in patients with CIDP. Recent
studies have shown that sonographic enlargement of proximal
median nerve segments in the arms and brachial plexus is a
differentiating feature of CIDP . In Charcot Marie Tooth (CMT)
disease, the nerve enlargement is more diffuse along the entire
course of the nerve specifically in type 1 A .
This distinction is important from prognostic and therapeutic
points of view; US can be more sensitive than EDX . showing
multifocal ulnar and median nerve enlargement. There is also
a recent report of US detecting treatment-responsive chronic
neuropathies without EDX features of demyelination .
While the clinical presentation and EDX findings are
often sufficient to make a diagnosis of neuralgic amyotrophy
(Parsonage Turner syndrome), MR neurography and US have
shown enlargement of peripheral nerve/fascicles and features of
nerve torsion or fascicular entwinement. In one study nerves with
complete constriction and rotational phenomena failed to show
significant reinnervation; these features, if detected by US may be
an indication for surgical intervention .
The needle electrode can pick up fasciculations from only
a limitedl area around it; also, it can be painful to have needle
inserted into structures like the tongue. US has the advantage
of visualizing fasciculations from a much wider area without
the pain involved in multiple needle insertions. Recent studies
have documented that US is much superior to EDX in detecting
fasciculations in patients with ALS .
The main question for preoperative planning are whether the
lesion is actually arising from the nerve and if not, anatomically
how close is it to the nerve. US provides immediate answers; it can
easily identify nerve tumors like schwannomas and neurofibromas
and also alert the surgeon to the potential for perioperative nerve
injury while removing lesions in close proximity to the nerve.
a. Distinction between muscular dystrophies and
inflammatory myopathies often made by EDX can be further
substantiated using US .
b. While EDX suggests a myopathic disorder, US can point
to a more precise diagnosis, based on the topography of muscle
involvement. The classical example is sporadic inclusion body
myositis (IBM) in which there is increased echogenicity of flexor
digitorum profundus with sparing of flexor carpi ulnaris [15, 16].
a. Dynamic US is useful to document mobility of median
nerve within the carpal tunnel and to document subluxation of the
ulnar nerve at the elbow.
b. Another major use is imaging of diaphragm for diagnosis
of phrenic nerve palsy; measurement of diaphragm thickness is
being used increasingly in ALS and myopathies .
c. Rarely the patient may not be able to tolerate electric
stimulation and needle study. This may particularly apply to
pediatric patients. US may provide an alternate route to reach the
While it is ideal to perform ultrasound evaluation in every
patient referred for EDX studies, it may not be feasible in a busy
clinical EDX lab due to time constraints. It is important to have
guidelines that identify situations where additional use of US
can provide vital information that will help in the diagnosis and
management of patients. It is likely that in the future an increasing
percentage of patients seen for EDX will also undergo US, as the
knowledge base of ultrasonic findings in various neuromuscular
disorders increase and as US technology advances with more