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Alternative names:

Lack of strength; Muscle weakness


A reduction in the strength of one or more muscles.


Weakness is a very important symptom. The feeling of weakness may be subjective (the person feels weak but has no measurable loss of strength) or concrete (measurable loss of strength). Weakness may be generalized (total body weakness) or localized to a specific area, side of the body, limb, and so on.

A subjective feeling of weakness usually is generalized and associated with infectious diseases such as infectious mononucleosis and influenza.
Weakness is particularly important when it occurs in only one area of the body (localized or focal weakness). Localized weakness may follow a stroke, exacerbation of multiple sclerosis, or trauma to a motor nerve root or peripheral nerve.

Common causes:

Measurable weakness may result from a variety of conditions including metabolic, neurologic, primary muscular diseases, and toxic disorders.


  • Diabetes
  • Addison’s disease
  • Thyrotoxicosis


  • Stroke(often focal or localized weakness)
  • Multiple sclerosis (may be focal)
  • Amyotrophic lateral sclerosis (focal developing to generalized)
  • Cerebral palsy (focal weakness associated with spasticity)
  • Guillain-Barre syndrome
  • Peroneal muscular atrophy
  • Werdnig-Hoffmann disease (spinal muscular atrophy)

Primary Muscular Disease

  • Muscular dystrophy (Duchenne)
  • Becker muscular dystrophy
  • Myotonic dystrophy
  • Dermatomyositis


  • Organophosphate poisoning (insecticides,nerve gas)
  • Paralytic shellfish poisoning
  • Botulism


  • Myasthenia gravis (an autoimmune disorder that interferes with the transmission of nerve impulses to muscle)
  • Poliomyelitis (an infectious disease that damages motor neurons)
  • Periodic paralysis (potassium related, such as hypokalemic periodic paralysis)


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