Muscular Dystrophy

Muscular dystrophy is an umbrella term for genetic conditions that cause gradual weakening and wasting of muscles.

The main muscular dystrophy to know about for the purpose of exams is Duchennes muscular dystrophy. It is worth being aware of the others.

 

Types

  • Duchennes muscular dystrophy
  • Beckers muscular dystrophy
  • Myotonic dystrophy
  • Facioscapulohumeral muscular dystrophy
  • Oculopharyngeal muscular dystrophy
  • Limb-girdle muscular dystrophy
  • Emery-Dreifuss muscular dystrophy

 

Gower’s Sign

Children with proximal muscle weakness use a specific technique to stand up from a lying position. This is called Gower’s sign.

To stand up, they get onto their hands and knees, then push their hips up and backwards like the “downward dog” yoga pose. They then shift their weight backwards and transfer their hands to their knees. Whilst keeping their legs mostly straight they walk their hands up their legs to get their upper body erect. This is because the muscles around the pelvis are not strong enough to get their upper body erect without the help of their arms.

TOM TIP: Gower’s sign is a favourite in exams. If there is a 5 year old boy presenting with vague symptoms of muscle weakness and the description is that you notice them using their hands on their legs to help them stand up, the answer is probably Duchennes muscular dystrophy. They may ask “what is the underlying genetic inheritance of the most likely cause?” The answer is X-linked recessive.

 

Management

There is no curative treatment for muscular dystrophy. Management is aimed at allowing the person to have the highest quality of life for the longest time possible. This usually involves input from occupational therapy, physiotherapy and medical appliances (such as wheelchairs and braces) as well as surgical and medical management of complications such as spinal scoliosis and heart failure.

 

Duchennes Muscular Dystrophy

Duchennes muscular dystrophy is the most likely muscular dystrophy to turn up in your exams. It is caused by a defective gene for dystrophin on the X-chromosome. Dystrophin is a protein that helps hold muscles together at the cellular level. Given that boys have a single X-chromosome and girls have two, girls have a spare copy of the dystrophin gene. Female carriers of the condition do not usually notice any symptoms. This makes Duchennes muscular dystrophy an X-linked recessive condition. If a mother is a carrier (meaning she has one faulty gene) and she has a child, that child will have a 50% change of being a carrier if they female and 50% change of having the condition if they are male.

Boys with Duchennes present around 3 – 5 years with weakness in the muscles around their pelvis. The weakness tends to be progressive and eventually all muscles will be affected. They are usually wheelchair bound by the time they become a teenager. They have a life expectance of around 25 – 35 years with good management of the cardiac and respiratory complications.

Oral steroids have been shown to slow the progression of muscle weakness by as much as two years. Creatine supplementation can give a slight improvement in muscle strength. Genetic trials are ongoing.

 

Beckers Muscular Dystrophy

Beckers muscular dystrophy is very similar to Duchennes, however the dystrophin gene is less severely affected and maintains some of its function. The clinical course is less predictable than Duchennes. Symptoms only start to appear around 8 – 12 years. Some patient require wheelchairs in their late 20s or 30s . Others able to walk with assistance into later adulthood. Management is similar to Duchennes.

 

Myotonic Dystrophy

Myotonic dystrophy is a genetic disorder that usually presents in adulthood. Typical features are:

  • Progressive muscle weakness
  • Prolonged muscle contractions
  • Cataracts
  • Cardiac arrhythmias

TOM TIP: The key feature of myotonic dystrophy to remember is the prolonged muscle contraction. This may present in exams with a patient that is unable to let go after shaking someones hand, or unable to release their grip on a doorknob after opening a door. When doing an upper limb neurological examination always shake the patients hand and observe for difficulty releasing their grip.

 

Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy usually presents in childhood with weakness around the face, progressing to the shoulders and arms. A classic initial symptom is sleeping with their eyes slightly open and weakness in pursing their lips. They are unable to blow their cheeks out without air leaking from their mouth.

 

Oculopharyngeal Muscular Dystrophy

Oculopharyngeal muscular dystrophy usually presents in late adulthood with weakness of the ocular muscles (around the eyes) and pharynx (around the throat) as the name suggests. It typically presents with bilateral ptosis, restricted eye movement and swallowing problems. Muscles around the limb girdles are also affected to varying degrees.

 

Limb-girdle Muscular Dystrophy

Limb-girdle muscular dystrophy usually presents in teenage years with progressive weakness around the limb girdles (hips and shoulders).

 

Emery-Dreifuss Muscular Dystrophy

Emery-Dreifuss muscular dystrophy usually presents in childhood with contractures, most commonly in the elbows and ankles. Contractures are shortening of muscles and tendons that restrict the range of movement in limbs. Patients also suffer with progressive weakness and wasting of muscles, starting with the upper arms and lower legs.

 

Last updated January 2020
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