Weakness is reduced strength in one or more muscles.

Lack of strength; Muscle weakness

Weakness may be all over the body or in only one area, side of the body, limb, or muscle. Weakness is more noticeable when it is in one area. Weakness in one area may occur:

• After a stroke
• After injury to a nerve
• During a flare-up of multiple sclerosis

Weakness may be subjective or objective:

• Subjective means you feel weak, but there is no real loss of strength. For example, you may feel weak if you have an infection such as mononucleosis or the flu.
• Objective means there is a loss of strength that can be noted during a physical exam.

Weakness may be caused by a variety of conditions, including:

METABOLIC

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

BRAIN/NERVOUS SYSTEM (NEUROLOGIC)

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

MUSCLE DISEASES

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

POISONING

• Botulism
• Poisoning (insecticides, nerve gas)
• Shellfish poisoning

OTHER

• Anemia
• Myasthenia gravis
• Polio

Follow the therapy your health care provider recommended to treat the cause of the weakness.

Call your health care provider if you have:

• Sudden weakness, especially if it is in one area and does not occur with other symptoms, such as fever
• Sudden weakness after a viral illness
• Unexplained weakness that does not go away
• Weakness in one area of the body

The health care provider 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?
  • Do you notice the weakness only after strenuous activity or exercise?
  • Did it start after a viral illness, such as a cold?
  • Did it start after a vaccination?
• Quality
  • Is the weakness constant or does it come and go, sometimes affecting different parts of your body?
  • Does the weakness affect your breathing?
  • Does it affect talking, chewing, or swallowing?
  • Does it affect walking, climbing stairs, sitting, or getting up?
  • Does it affect the use of your 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?
• Factors that make the weakness worse
  • What makes the weakness worse?
    • Fatigue
    • Hunger
    • Pain
    • Physical activity
    • Rest
    • Stress
• Relieving factors
  • Does anything help relieve the weakness?
    • Eating
    • Pain relief
    • Rest
• Other symptoms
  • What other symptoms do you have?
    • Change in mental state, alertness, or responsiveness
    • Change in skin color or temperature of the affected area
    • Changes in vision
    • Diarrhea
    • Fever
    • Headaches
    • Injury
    • Numbness or tingling
    • Pain
    • Vomiting
    • Weight loss
• Other important information
  • What medications do you take?
  • Do you have any allergies?

The physical examination may include special attention to your heart, lungs, and thyroid gland. If there is a local area of weakness, the examination will focus on the nerves and muscle.

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

Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 403.

Chinnery PF. Muscle diseases. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 429.