Muscular dystrophy

Alternative names

Inherited myopathy; MD

Definition

Muscular dystrophy is a group of disorders characterized by progressive muscle weakness and loss of muscle tissue.

Causes, incidence, and risk factors

The group of diseases called muscular dystrophies (MD) includes many inherited disorders such as:

• Becker's muscular dystrophy
  
• Duchenne muscular dystrophy
  
• facioscapulohumeral muscular dystrophy
  
• limb-girdle muscular dystrophy
  
• Emery-Dreifuss muscular dystrophy
  
• myotonic dystrophy
  
• myotonia congenita
  

These disorders are distinguished from each other by the type of inheritance (sex-linked, dominant gene, recessive gene), the age when symptoms appear, and the types of symptoms that develop. Because these are inherited disorders, risks include a family history of muscular dystrophy.

Lambert-Eaton syndrome and myasthenia gravis also have symptoms that may be similar to early stages of some types of muscular dystrophies, so these disorders must be ruled out when muscular dystrophies are diagnosed.

Symptoms

Symptoms vary with the different types of muscular dystrophy. Some types, such as Duchenne muscular dystrophy, are ultimately fatal while other types have associated muscle weakness but cause little disability and are associated with normal life expectancy.

The muscles primarily affected vary, but can be around the pelvis, shoulder, face or elsewhere. The age of onset can vary as well, with more severe subtypes tending to occur earlier in childhood.

• muscle weakness
  o progressive
  o frequent falls
  o delayed development of muscle motor skills
  o problems walking (delayed walking)
  o difficulty using one or more muscle groups (the specific muscles affected depends on the type of MD)
  o eyelid drooping (ptosis)
  o drooling
  
• mental retardation (only present in some types of MD)
  
• hypotonia (low muscle tone)
  
• joint contractures (clubfoot, clawhand, or others)
  
• scoliosis (curved spine)
  

Signs and tests

Examination and history help to distinguish the type of MD. Specific muscle groups are affected by different types of MD. Often, there is a loss of muscle mass (wasting), which may be disguised in some types of muscular dystrophy by an accumulation of fat and connective tissuethat makes the muscle appear larger (pseudohypertrophy).