What causes muscle weakness?

Muscle weakness is a decrease in muscle strength, and it can be caused by a neurologic, muscular or metabolic disorder. Neurologic disorders causing muscle weakness include amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease), Guillain-Barre syndrome (an autoimmune nerve disorder), stroke, or even a pinched nerve.

Muscular disorders, such as muscular dystrophy and dermatomyositis, are also common causes of muscular weakness. Metabolic conditions that can lead to weakness include Addison’s disease, low sodium or potassium levels, and hyperparathyroidism. Ingestion of toxic substance, such as insecticides, nerve gas, or paralytic shellfish poisoning, can cause muscle or nerve damage along with muscle weakness. Muscle weakness can also result from blood disorders, such as anemia and low blood sugar (hypoglycemia).

Metabolic causes of muscle weakness

Muscle weakness may have metabolic causes including:

  • Addison’s disease (deceased production of hormones by the adrenal glands)
  • Hyperparathroidism (overactive parathyroid glands)
  • Hyperthyroidism (overactive thyroid)
  • Hypokalemia (low potassium)
  • Hyponatremia (low sodium)

Neurological causes of muscle weakness

Muscle weakness may have neurological causes including:

  • Bell’s palsy (swollen or inflamed nerve that controls facial muscles)
  • Cerebral palsy (group of conditions affecting the brain and nervous system functions)
  • Charcot-Marie-Tooth disease (inherited disorder affecting the peripheral nerves)
  • Guillain-Barre syndrome (autoimmune nerve disorder)
  • Multiple sclerosis (disease that affects the brain and spinal cord, causing weakness, coordination and balance difficulties, and other problems)
  • Nerve entrapment or compression, such as of the ulnar nerve in the arm
  • Stroke

Muscular disease causes of muscle weakness

Muscle weakness may have muscular disease causes including:

  • Amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease, a severe neuromuscular disease that causes muscle weakness and disability)
  • Dermatomyositis (condition characterized by muscle inflammation and skin rash)
  • Muscular dystrophy (inherited disorder that causes a progressive loss of muscle tissue and muscle weakness)

Toxic causes of muscle weakness

Muscle weakness may be due to toxins including:

  • Botulism (serious food poisoning caused by Clostridium botulinum bacterium)
  • Insecticide ingestion
  • Nerve gas exposure
  • Paralytic shellfish poisoning

Other causes of muscle weakness

Muscle weakness may have other causes including:

  • Anemia (low red blood cell count)
  • Overuse injury (overuse of a muscle)
  • Polymyositis (widespread inflammation and weakness of muscles)

Serious or life-threatening causes of muscle weakness

In some cases, muscle weakness may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These conditions include:

  • Botulism (serious food poisoning caused by Clostridium botulinum bacterium)
  • Stroke
  • Transient ischemic attack (temporary stroke-like symptoms that may be a warning sign of an impending stroke)

Questions for diagnosing the cause of muscle weakness

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your muscle weakness including:

  • How long have you felt muscle weakness?
  • Where do you feel muscle weakness?
  • Do you have any other symptoms?
  • What medications are you taking?

What are the potential complications of muscle weakness?

Because muscle weakness can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

  • Loss of mobility
  • Paralysis
  • Permanent loss of sensation
  • Permanent nerve damage (due to a pinched nerve), including paralysis
  • Spread of infection


  1. Weakness. MedlinePlus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003174.htm.
  2. Hereditary condition causing limb weakness traced to gene for rare disorder. NIH News. http://www.nih.gov/news/health/mar2010/nichd-11.htm.

What is muscle weakness?

Muscle weakness, or myasthenia, is a decrease in strength in one or more muscles. It is a common symptom of muscular, neurological and metabolic disorders.... Read more about muscle weaknessintroduction


What other symptoms might occur with muscle weakness?

Muscle weakness may accompany other symptoms, which vary depending on the underlying disease, disorder or condition. Symptoms that frequently affect the muscles may also involve other body systems.

Muscular symptoms that may occur along with muscle weakness

Muscle weakness may accompany other symptoms affecting the muscles including:

Medical Reviewer: William C. Lloyd III, MD, FACS Last Annual Review Date: Sep 6, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Bones, Joints and Muscles

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