DELAY IN AGE OF WALKING CAN HERALD MUSCULAR DYSTROPHY IN BOYS WITH COGNITIVE DELAYS
The timing of a
toddler's first steps is an important developmental milestone, but a slight
delay in walking is typically not a cause of concern by itself.
Now a duo of Johns
Hopkins researchers has found that when walking and cognitive delays occur in
concert, the combination could comprise the earliest of signals heralding a
rare but devastating disorder known as Duchenne muscular dystrophy (DMD).
The study, published
ahead of print in The Journal of Pediatrics and conducted by a
medical student and a pediatric neurologist, reveals that delays in the onset
of walking -- which should occur between 9 and 16 months of age -- are common
among boys with DMD and often happen alongside cognitive delays. That combination,
the investigators say, can give pediatricians a critical early diagnostic clue
and tip them off to the presence of DMD.
"Our review of
patient records shows that delayed walking along with cognitive delays
represents an ominous combination that should prompt pediatricians to conduct
further testing and could speed up diagnosis and treatment," says Kara
Mirski, a fourth-year medical student at the Johns Hopkins University School of
Medicine. "Earlier diagnosis means that we can start treating these kids
sooner and greatly improve their long-term outcomes."
DMD is caused by a
defective muscle protein. It is marked by progressive loss of muscle strength
and function and, eventually, inability to walk at all. In its advanced forms,
the condition can also compromise the function of the heart and breathing
muscles. DMD, which almost exclusively affects males, is estimated to occur in
one out of 3,500 boys.
Current guidelines
from the American Academy of Neurology and the Child Neurology Society do not
include DMD on the suspected diagnoses list for boys with developmental delays.
While neither cognitive delays nor delayed walking by themselves are
necessarily caused by DMD, when the two occur in tandem they should raise the
index of suspicion and seriously narrow the range of diagnostic possibilities,
the team says.
"The bottom line
is that any delay in walking should lead to further probing, or at least
vigilant monitoring, and when late walking occurs in the context of other
developmental delays, it should put DMD on every pediatrician's radar as a
possible cause," says study author Tom Crawford, M.D., a pediatric
neurologist and muscular dystrophy expert at the Johns Hopkins Children's
Center.
Once a physician
suspects DMD, a child can be screened further with a cheap and widely available
test that measures the blood levels of creatinine kinase (CK), a protein
released as a result of muscle damage or muscle cell death. Normal CK levels
rule out DMD.
Once diagnosis is
made, treatment with steroids and physical therapy can halt or slow muscle
damage and help preserve mobility and function, the researchers say. In
addition, because most cases of DMD are inherited, earlier diagnosis would
allow families to consult a genetic counselor who can help them make informed decisions
about subsequent pregnancies.
DMD can be easily
missed during the infant and toddler years, even among children with
developmental delays, Crawford notes. The condition's characteristic muscle
weakness does not present at such an early age, and the absence of the
disease's defining symptom can easily throw off pediatricians. This is why,
Crawford says, any developmental delay should prompt pediatricians to probe
deeper.
In addition, while
most cases of DMD stem from inherited genetic defects, some genetic mutations
can arise spontaneously in families without history of the disorder. In those
cases, diagnosis can be delayed even further, until a child is 5 or 6 years
old, the researchers say.
For the study, the
investigators examined the clinical records of 107 children with DMD referred
to the Johns Hopkins Children's Center between 1989 and 2012 for diagnosis or
treatment. Nearly half (42 percent) had a history of delayed walking (age 16
months or later). Toddlers who started walking late were three times as likely
to have cognitive delays as those who began walking on time. The link between
the time of a child's first steps and cognitive delay persisted even when
investigators eliminated other factors such as the speed and severity of muscle
degeneration or age of diagnosis. The study also revealed that DMD patients who
started walking late were not referred for diagnostic work-up any earlier than
their counterparts who started walking at what is deemed a typical age. In
other words, delayed walking did not emerge as the red flag it should have
been, the investigators say.
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