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

Weakness may be generalized (total body weakness) or localized to only one area, side of the body, limb, or muscle. Weakness is more notable when it is localized. Localized weakness may follow a stroke, flare up of multiple sclerosis, or injury to a nerve.

Weakness may be subjective or objective.

• Subjective means you feel weak, but there is no measurable loss of strength. For example, you may feel weak if you have infectious diseases such as mononucleosis and the flu.
• Objective means there is a measurable loss of strength noted during a physical exam.

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

METABOLIC

• Addison's disease
• Hyperparathyroidism
• Low sodium or potassium
• Thyrotoxicosis

NEUROLOGIC

• Amyotrophic lateral sclerosis
• Bell's palsy
• Cerebral palsy
• Guillain-Barre syndrome
• Multiple sclerosis
• Pinched nerve (for example, caused by a slipped disk in the spine)
• Stroke

PRIMARY MUSCULAR DISEASES

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

TOXIC

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

OTHER

• Anemia
• Myasthenia gravis
• Poliomyelitis

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

Call your doctor if you have:

• Prolonged, unexplained weakness
• Sudden weakness, particularly when it is in one area and not accompanied by other complaints, such as fever
• Sudden weakness following a viral illness
• Weakness in one area of the body

The doctor will examine you and ask questions about your medical history and symptoms, such as:

• 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 do you have?
    • 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 responsiveness
• Additional important information
  • What medications do you take?
  • Do you have any allergies?

Physical examination may include special attention paid to examination of heart, lungs, and thyroid gland. If there is a local area of weakness, the examination will focus on the nerve and muscle functions.

Diagnostic tests that may be done include:

• Blood tests for autoimmune disorders
• Blood tests such as a CBC and electrolytes
• Lumbar puncture (CSF collection)
• MRI or CT scan of your head and spine
• Muscle biopsy
• Nerve conduction studies
• Thyroid function tests
• Urinalysis

Lack of strength; Muscle weakness

Griggs RC, Józefowicz RF, Aminoff MJ. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 418.

Barohn RJ. Muscle diseases. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 447.

Updated by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.