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Alternative names

Weakness is a reduction in the strength of one or more muscles.


Weakness may be subjective (the person feels weak, but has no measurable loss of strength) or objective (measurable loss of strength as noted in a physical exam). Weakness may be generalized (total body weakness) or localized to a specific area, side of the body, limb, or muscle.

A subjective feeling of weakness may be associated with infectious diseases such as infectious mononucleosis and influenza .

Weakness is more notable 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.


  • Addison's disease
  • Thyrotoxicosis
  • Stroke (often localized weakness)
  • Bell's palsy (weakness of one side of the face)
  • A nerve impingement syndrome such as a slipped disk in the spine
  • Multiple sclerosis (may be localized)
  • Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease; localized developing to generalized)
  • Cerebral palsy (localized weakness associated with spasticity )
  • Guillain-Barre syndrome
  • 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 ("polio" -- an infectious disease that damages motor neurons)
  • Dermatomyositis/polymyositis (autoimmune diseases leading to proximal muscle weakness, muscle pain, and sometimes skin rashes)

Home Care

Follow prescribed therapy for treating the underlying cause of the weakness.

Call your health care provider if

  • There is weakness confined to one area of the body.
  • There is prolonged, unexplained weakness.
  • You notice the sudden onset of weakness, particularly when it is localized and not accompanied by other complaints, such as fever.
  • You become suddenly quite weak following a typical viral illness.

The medical history will be obtained and a physical examination performed.

Medical history questions documenting the weakness in detail may include:
  • Time pattern
    • When did the weakness begin?
    • Did it begin with an illness or injury?
    • Did it occur suddenly or gradually?
    • Is the weakness worse in the morning or at night?
    • Is the weakness noticed only after strenuous activity or exercise?
    • Did it start following a typical viral illness, such as a cold?
    • Did it start after a vaccination?
  • Quality
    • Is the weakness constant or does it come and go, sometimes effecting different parts of your body?
    • Does the weakness affect breathing?
    • Does it affect talking, chewing, or swallowing?
    • Does it affect walking, climbing stairs, sitting, getting up?
    • Does it affect use of the hands, arms, or shoulders?
    • Is there pain with the weakness?
    • Is there numbness or tingling with the weakness?
  • Location
    • Is the weakness limited to a specific area?
    • Has the area of weakness increased or decreased?
  • Aggravating factors
    • What makes the weakness worse?
      • Physical activity
      • Rest
      • Hunger
      • Fatigue
      • Pain
      • Stress
  • Relieving factors
    • Does anything help relieve the weakness?
      • Rest
      • Eating
      • Pain relief
  • Other symptoms
    • What other symptoms are also present?
      • Fever
      • Injury
      • Pain
      • Numbness or tingling
      • Vomiting
      • Diarrhea
      • Weight loss
      • Headaches
      • Changes in vision
      • Change in skin color or temperature of the area affected
      • Change in mental state , alertness, or responses
  • Additional important information
    • What medications are being taken?
    • Are there any known allergies ?
Physical examination may include special attention paid to examination of heart, lungs, and thyroid gland. If there is localized weakness, the examination will focus on the nerve and muscle functions.

Diagnostic tests that may be performed include:
  • Thyroid function tests and other blood tests for endocrine disorders
  • Blood tests such as a CBC and electrolytes
  • Blood tests for autoimmune disorders
  • Urine tests ( urinalysis)
  • Nerve conduction studies
  • Lumbar puncture
  • MRI or Cat (CT) scan of your head and spine
  • Muscle biopsy
After seeing your health care provider:
You may want to add a diagnosis related to weakness to your personal medical record.

Update Date: 11/17/2003

David Webner, M.D., Sports Medicine Fellow, Crozer-Keystone Family Practice Program, Springfield, PA. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT