Duchenne muscular dystrophy (DMD) is one of the most severe forms of inherited muscular dystrophy.
This rare genetic disorder is due to the absence of a vital protein called dystrophin that helps the body maintain muscle cells, which results in rapid muscle degeneration and increasing muscle weakness. Symptoms begin in childhood, with patients eventually requiring a wheelchair and/or a breathing device.
Although there’s no cure for DMD, early diagnosis can help ensure timely access to treatment, counseling, and screening for complications, slowing disease progression and improving quality of life.
Here is an overview of how a Duchenne muscular dystrophy diagnosis works.
DMD symptoms in a child may send a parent or caregiver to the doctor, or prompt a doctor to send a child to a specialist for a confirmed diagnosis.
Typically boys are affected by DMD rather than girls, and they often experience the first symptoms between the ages of 2 and 5. These may include:
Using hands to get up from sitting or squatting, a movement called Gower’s sign
Trouble with running, jumping, and climbing stairs
Enlarged calves, also known as pseudohypertrophy (“false enlargement”) because the muscles look bigger even though they are weaker
Waddling
Leg pain
Difficulty climbing stairs
Short stature
Learning problems, which can happen as the disease disrupts brain activity that is essential for memory formation and consolidation.
As the condition progress, children may experience:
Shortness of breath or other breathing problems due to weakening of the diaphragm
Irregular heartbeat or other heart problems
While the symptoms observed by parents or other adults provide clues that a child has Duchenne, an accurate diagnosis requires a physical examination from a doctor, as well as testing.
Because Duchenne muscular dystrophy is inherited, healthcare practitioners will ask detailed questions about the patient’s family health history — specifically if anyone in the family is known to have had DMD, any other type of muscular dystrophy, or any kind of neuromuscular disease.
The physician will check whether the parents have noticed any of the telltale symptoms, and also perform their own assessment.
By having a patient complete a short walking test, move from a lying down position to a standing one, and climb up and down a few stairs, a medical professional may observe symptoms and establish the level of muscle performance and disease progression.
Exercises that test strength or weakness in specific muscles in upper and lower limbs may be part of a physical evaluation.
Electrodiagnostic tests (EMG/NCS) may be included in a diagnostic workup. These use a machine that measures electrical signals in muscles and nerves to assess how they are functioning.
After evaluating symptoms that may suggest Duchenne, physicians will typically turn to lab tests that can confirm the diagnosis:
Creatine Kinase (or CK Level) Blood Test Doctors take a blood sample to measure levels of creatine kinase, an enzyme that leaks out of damaged muscle. Elevated CK levels usually means that muscle is being disintegrated by some abnormal process, such as muscular dystrophy.
Genetic Testing A lab analysis of the DNA (the molecule that contains genetic information) in a blood or saliva sample can reveal whether there are genetic mutations that prevent muscles from producing the protein dystrophin. If the test comes back with the terms “Positive result,” “Mutation detected,” “Pathogenic variant detected,” or similar, it is confirmation of a DMD gene mutation.
Muscle Biopsy By taking a minute tissue sample from the thigh or calf, doctors can look at the cells under a microscope and get a clearer picture of what is happening inside the muscle. Specialists look for endomysial connective tissue proliferation — a type of abnormal tissue growth in patients with DMD that is apparent long before any muscle degeneration can be observed.
They also will note any general degeneration, abnormal cell death of muscle cells (necrosis), regeneration of myofibers (cells that make up skeletal muscle and rise with muscle injury), and replacement of muscle with adipose tissue and fat.
A biopsy involves injecting a numbing medicine, such as lidocaine, into the skin and muscle at the biopsy site, to reduce pain. The biopsy site may be tender for two to three days after the procedure.
Electrocardiogram (EKG) and Echocardiogram (Echo) DMD almost always affects the heart, and an EKG to check heartbeat and electrical signals can reveal characteristic symptoms of the disease. Abnormal rhythms suggest heart muscle damage.
While an EKG provides details about the heart’s electrical activity, a doctor may want to look more closely at the structure of the heart using an echocardiogram, which uses high-frequency sound waves (ultrasound) to make pictures of the organ. Studies have shown improvement in the early diagnosis of DMD-related cardiomyopathy with advanced echocardiogram techniques.
With DMD, cardiac function worsens, and heart failure can develop. Based on EKG and echocardiogram readings, doctors may prescribe medications that help heart function.
A few states (such as Ohio, Minnesota, New York, and Massachusetts) now mandate genetic testing for Duchenne muscular dystrophy in all newborns as part of a standard array of blood tests. Other states may follow suit.
Parents interested in genetic testing for their newborn may also want to check out Parent Project Muscular Dystrophy’s genetic testing program, Decode Duchenne, which provides free genetic testing to eligible individuals.
Primary care physicians and pediatricians are often the first healthcare professionals to identify signs of Duchenne.
A consultation with an expert, such as a pediatric neurologist or neuromuscular specialist, is likely needed to confirm a Duchenne muscular dystrophy diagnosis.
Specialists who have years of experience with DMD can more readily recognize its symptoms and guide patients toward treatments, such as corticosteroids, which can decrease the rate of declining strength.
They can also direct patients to physical and occupational rehabilitation professionals who can teach children strengthening exercise programs and activities, orthopedic surgeons who may treat severe tightening of the muscles (contractures) and scoliosis (curvature of the spine), pediatric cardiologists who can evaluate heart function, and mental health specialists who can assist with the emotional strains of this illness.
Symptoms of Duchenne muscular dystrophy often appear at a young age, and recognizing these signs is the first step in diagnosing DMD.
A detailed physical exam by a doctor, along with a series of lab tests, will help confirm whether a patient has DMD.
Genetic testing soon after birth is becoming more widespread as public health officials recognize that early detection and treatment can slow patients’ disease progression and improve their quality of life.
