Duchenne Muscular Dystrophy (DMD)

Signs and Symptoms

Weakness related to Duchenne muscular dystrophy (DMD) selectively affects the limb muscles close to the trunk before the ones far from it; the legs are affected before the arms. Growth velocity with DMD is typically slower than normal in the first years of life, leading to short stature.

Boys with DMD are often late walkers.

Variations in the gene LTBP4 and the regulatory region of the gene SPP1 are known to influence the age of loss of ambulation and/or the decay in muscle strength.^1,2,3,4,5 In toddlers, parents may notice enlarged calf muscles (see image at right). This enlargement is known as pseudohypertrophy, or "false enlargement," because the muscle tissue is abnormal.Pseudohypertrophy can also occur in the muscles of the thighs. Pseudohypertrophy can also occur in the muscles of the thighs.

A preschooler with DMD may seem clumsy and fall often. Parents also may note that children have trouble climbing stairs, getting up from the floor, or running. When arising from the floor, affected boys may use hand support to push themselves to an upright position.

By school age, children may walk on their toes or the balls of their feet with a slightly waddling gait and fall frequently. To try to keep their balance, they may stick out their bellies and pull back their shoulders. Children also have difficulty raising their arms.

Many children with DMD begin using a wheelchair sometime by the age of 12. Transition to a wheelchair usually is a gradual process; at first, the chair may be required only to conserve the child's energy when covering long distances. Children often experience renewed independence once they fully transition to a power wheelchair.

In the teen years, activities involving the arms, legs, or trunk may require assistance or mechanical support.

Patients with DMD often die in their late teens or 20s from respiratory insufficiency or cardiomyopathy; only a few DMD patients survive beyond the third decade.

Pain and sensation

The muscle deterioration in DMD is not usually painful in itself. Some people report muscle cramps at times; these usually can be treated with over-the-counter pain relievers.

Because muscular dystrophy does not affect nerves directly, touch and other senses are normal, as is control over the smooth, or involuntary, muscles of the bladder and bowel, and sexual functions.

The heart

Lack of dystrophin can weaken the muscle layer in the heart (myocardium), resulting in a condition called cardiomyopathy, characterized by extensive scarring of the tissue. DMD also can cause conduction abnormalities in the heart. It has been reported that all patients older than 18 present symptoms of cardiomyopathy. Over time, sometimes as early as the teen years, the damage done by DMD to the heart can become life-threatening. The heart should be monitored closely, usually by a pediatric cardiologist. See Medical Management for more on cardiomyopathy in DMD.

Respiratory function

Serial monitoring of breathing capacity should start at the age of 5 or 6. The diaphragm and other muscles that operate the lungs may weaken, making the lungs less effective at moving air in and out. Although a child may not complain of shortness of breath, problems that indicate poor respiratory function include headaches, mental dullness, difficulty concentrating or staying awake, and nightmares. Wheelchair-bound children tend to have evidence of poor pulmonary function.

Weakened respiratory muscles make coughing difficult, leading to increased risk of serious respiratory infection. A simple cold can quickly progress to pneumonia. It is important to get a flu vaccine, and when infections occur, to get prompt treatment. See Medical Management for more on respiratory care in DMD.

Learning

About a third of boys with DMD have some degree of learning disability, although few have serious cognitive disability. Doctors believe that dystrophin abnormalities in the brain may have subtle effects on cognition and behavior. Learning problems in DMD occur in three general areas: attention focusing, verbal learning and memory, and emotional interaction.

Children suspected of having a learning disability can be evaluated by a developmental or pediatric neuropsychologist through the school system’s special education department or with a referral from an MDA Care Center.

If a learning disability is diagnosed, educational and psychological interventions can begin right away. A specialist may prescribe exercises and techniques that can help improve these areas, and schools also can provide special help with learning. See Medical Management for more about learning disabilities in DMD.

References

1. Hightower, R. M. & Alexander, M. S. Genetic modifiers of Duchenne and facioscapulohumeral muscular dystrophies. Muscle and Nerve (2018). doi:10.1002/mus.25953
2. Van Den Bergen, J. C. et al. Validation of genetic modifiers for Duchenne muscular dystrophy: A multicentre study assessing SPP1 and LTBP4 variants. J. Neurol. Neurosurg. Psychiatry (2015). doi:10.1136/jnnp-2014-308409
3. Bello, L. et al. Genetic modifiers of ambulation in the cooperative international Neuromuscular research group Duchenne natural history study. Ann. Neurol. (2015). doi:10.1002/ana.24370
4. Flanigan, K. M. et al. LTBP4 genotype predicts age of ambulatory loss in duchenne muscular dystrophy. Ann. Neurol. (2013). doi:10.1002/ana.23819
5. Pegoraro, E. et al. SPP1 genotype is a determinant of disease severity in Duchenne muscular dystrophy. Neurology (2011). doi:10.1212/WNL.0b013e318207afeb