When diagnosing and treating pediatric spinal muscular atrophy (SMA), doctors need to understand a child’s physical abilities to determine how severe the disease is. To do this, they use a variety of tests that measure motor function — how well a person is able to move and control their muscles. The Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) examination is a tool designed to help measure motor abilities in children with SMA.
CHOP INTEND is a test that provides information about how strong a child’s muscles are and how well the child can control these muscles. This tool can help doctors measure motor milestones (certain physical skills usually achieved at certain points during development). It is the most popular test used to assess motor function in people with SMA.
CHOP INTEND was originally designed as a test for infants with SMA type 1 (Werdnig-Hoffmann disease). This type of SMA is usually diagnosed within the first six months of life and leads to many muscle problems. In more recent years, however, studies have found that CHOP INTEND may help measure muscle function for adults with SMA type 2 who are experiencing severe muscle weakness.
Researchers developed CHOP INTEND after studying how SMA progresses over time when left untreated. CHOP INTEND is based on older motor skills tests, including the Test of Infant Motor Performance.
CHOP INTEND is often used during regular doctor’s visits. It is also useful within clinical trials, where it helps researchers learn more about SMA and its treatments.
Doctors can use CHOP INTEND to assess motor skills when a person is first diagnosed with SMA. Then, doctors can perform this test regularly in the future to see how a person’s physical function is changing over time.
Doctors may also use other tests to measure motor function, such as the Hammersmith Infant Neurological Examination, the Hammersmith Functional Motor Scale, or the Motor Function Measure. The tests that a child receives depend on their age, type of SMA, and whether they are able to sit or walk. CHOP INTEND is most useful for very young infants or children, or older children or adults experiencing extreme muscle weakness.
This assessment is also useful when evaluating potential new SMA treatments. For example, if a new therapy is effective, the CHOP INTEND scores of people using the new therapy may increase. Several clinical trials have used this test, including:
Doctors often perform motor function tests every six months for children with SMA. In certain cases, a doctor may recommend that these tests be carried out more or less often.
The CHOP INTEND test is given by a doctor or physical therapist. It typically takes about 10 to 15 minutes. During this time, the health care provider will work with the caregiver to test different motor skills. To get the most accurate results, the person being tested should be relatively comfortable — they shouldn’t be tired or hungry.
During the CHOP INTEND exam, the health care provider measures 16 types of muscle movements. These include things like head control (keeping the head upright), elbow flexion and knee extension (bending the joints), arm and leg mobility, and handgrip. Each of the 16 motor skills is given a score from 0 to 4:
All of these scores are added up to give one total score. The highest possible score for the CHOP INTEND test is 64.
Infants with SMA generally have a lower CHOP INTEND score than children without SMA. A low score may indicate that a child is experiencing muscle weakness from SMA. There may also be other factors, such as age and developmental status, that affect the final score.
CHOP INTEND scores decrease over time if the disease is left untreated, as the disease progresses and muscle weakness gets worse. CHOP INTEND scores also tend to drop gradually after diagnosis.
A person’s genetics also affects their SMA score. SMA develops when people don’t have a working survival motor neuron 1 (SMN1) gene. As a result, the cells don’t make enough survival motor neuron (SMN) protein. This protein is important for healthy motor neurons, or nerve cells that connect the brain to the muscles. Another SMN gene, the SMN2 gene, also makes SMN protein, although not as much as SMN1. People with more copies of the SMN2 gene make more SMN protein. Studies have found that people with fewer copies of SMN2 tend to have more severe disease and lower CHOP INTEND scores.
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