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Diagnosing
SMA
*This information is not to take the place of
actual medical advice. If you have a question, always consult with
your physician.*
Physical
Characteristics:
The common physical
characteristics of SMA include:
-
"Frog"
shaped legs (knees apart and legs bent)
-
a
sunken or narrow chest
-
a
big belly
-
breathing
with the belly instead of the lungs
-
a
weak cry and weak cough
-
poor
to no head/neck control; head tilted to one side
-
weak
if any movement of the legs and upper arms
-
not
able to bear any weight on legs or arms
-
hands
that remain clenched or turned the wrong way
-
difficulty
sucking and swallowing
-
tongue
fasciculations (tongue vibrating rapidly).
These characteristics vary in
severity depending on how advanced the SMA is in each child. Some of
these characteristics may not show up until later.
Medical Testing:
There are several
medical tests that can be performed to diagnose SMA. Following are a
listing of the tests along with an explanation of how they are performed
and their accuracy:
EMG
(Electromyography)
An EMG test measures the electrical activity of muscle. In this procedure
small needles are gently inserted into the patient's muscles
(usually the arms and thighs) while an electrical pattern is observed and
recorded by a specialist.
At the same time, a nerve conduction velocity (NVC) will probably also be
performed. This uses the same needles and equipment. In this test
the response of a nerve to an electrical stimulus is measured. When
performing this test on a child, if at all possible, it should be
performed by a doctor experienced in dealing with children. If permitted,
hold your child on your lap during the procedure, to make an unpleasant
procedure somewhat bearable. Your doctor may allow your child to be given
a mild pain killer or sedative prior to the test.
Genetic Blood Test
Within the last decade, a blood test
has now become available to detect SMA. This blood test works by
detecting deletions in gene sequences that are not missing in normal,
healthy individuals. This blood test can not tell the Type of SMA
that the individual has (Type I, II, or III), and approximately 5% of
individuals who do have SMA do not show the gene deletions. However,
for the 95% of individuals who do show the deletions, the diagnosis is
100% accurate, and the Type of SMA can be determined by other physical
factors. With a blood test to screen for SMN deletion together with
an EMG and a clinical examination it may not be necessary for a muscle
biopsy to be performed. If the results show that there is no
deletion of the SMN gene, but the clinical examination and the EMG still point
to SMA, than a muscle biopsy would be necessary to confirm the diagnosis.
Muscle Biopsy
This is a surgical procedure where an incision approximately 3 inches long
is made, and a small section of muscle is removed. Usually they
remove the muscle from the upper thigh. The biopsy is used to check for
degeneration of muscles and special tell-tale signs in the muscles of
SMA. It is important to find a doctor used to dealing with children,
and experienced in dealing with SMA. Although many doctors may persuade
you of the necessity of a general anesthetic, this procedure can be done
with a local anesthetic. This is especially important when dealing with
children who are possibly suffering from SMA which includes by nature a
weak respiratory system. General anesthesia is not recommended for
children with neuromuscular diseases such as SMA as it may be difficult
for them to recover.
Needle Biopsy
There is now an alternative to a muscle biopsy. Instead of a 2-3 inch
incision, only a small nick in the skin is necessary. Be sure to ask
your doctor about this possibility.
Bottom Line:
You have several options
when testing for SMA. My PERSONAL opinion and recommendation, is
that the blood test is by far the easiest, least painful and least
invasive of all the options, and accurately diagnoses SMA in 95% of
cases. I would recommend going with the blood test first. If
the blood test comes back negative for SMA, then a muscle biopsy/EMG will
be necessary. If it comes back positive, that will be 100% accurate.
Of course, at all times follow your doctor's orders! |
