Muscle function loss is when a muscle doesn't work or move normally. The medical term for complete loss of muscle function is paralysis.

Paralysis; Paresis; Loss of movement; Motor dysfunction

Loss of muscle function may be caused by:

• A disease of the muscle itself (myopathy)
• A disease of the nervous system: nerve damage (neuropathy), spinal cord or nerve injury, or brain damage (stroke or other brain injury)

The loss of muscle function after these types of events can be severe. Often it will not completely return, even with treatment.

Paralysis can be temporary or permanent. It can affect a small area (localized) or be widespread (generalized). It may affect one side (unilateral) or both sides (bilateral).

If the paralysis affects the lower half of the body and both legs it is called paraplegia. It if affects both arms and legs, it is called quadriplegia. If the paralysis affects the muscles that cause breathing, it is quickly life threatening.

Diseases of the muscles that cause muscle-function loss include:

• Alcohol-associated myopathy
• Congenital myopathies (usually due to a genetic disorder)
• Dermatomyositis and polymyositis
• Drug-induced myopathy (statins, steroids)
• Muscular dystrophy

Diseases of the nervous system that cause muscle function loss include:

• Amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease)
• Bell's palsy
• Botulism
• Guillain-Barre syndrome
• Myasthenia gravis
• Neuropathy
• Paralytic shellfish poisoning
• Periodic paralysis
• Peroneal nerve injury
• Polio
• Spinal cord injury
• Stroke

Sudden loss of muscle function is a medical emergency. Seek immediate medical help.

After you have received medical treatment, your doctor may recommend some of the following measures:

• Follow your prescribed therapy.
• If the nerves to your face or head are damaged, you may have difficulty chewing and swallowing or closing your eyes. In these cases, a soft diet may be recommended. You will also need some form of eye protection, such as a patch over the eye while you are asleep.
• Long-term immobility can cause serious complications. Change positions often and take care of your skin. Range-of-motion exercises may help to maintain some muscle tone.
• Splints may help prevent muscle contractures, a condition in which a muscle becomes permanently shortened.

Muscle paralysis always requires immediate medical attention. If you notice gradual weakening or problems with a muscle, get medical attention as soon as possible.

The doctor will perform a physical examination and ask questions about your medical history and symptoms, including:

• Location
  • What part(s) of your body are affected?
  • Does it affect one or both sides of your body?
  • Did it develop in a top-to-bottom pattern (descending paralysis), or a bottom-to-top pattern (ascending paralysis)?
  • Do you have difficulty getting out of a chair or climbing stairs?
  • Do you have difficulty lifting your arm above your head?
  • Do you have problems extending or lifting your wrist (wrist drop)?
  • Do you have difficulty gripping (grasping)?
• Symptoms
  • Do you have pain?
  • Do you have numbness, tingling, or loss of sensation?
  • Do you have difficulty controlling your bladder or bowels?
  • Do you have shortness of breath?
  • What other symptoms do you have?
• Time pattern
  • Do episodes occur repeatedly (recurrent)?
  • How long do they last?
  • Is the muscle function loss getting worse (progressive)?
  • Is it progressing slowly or quickly?
  • Does it become worse over the course of the day?
• Aggravating and relieving factors
  • What, if anything, makes the paralysis worse?
  • Does it get worse after you take potassium supplements or other medications?
  • Is it better after you rest?

Tests that may be performed include:

• Blood studies (such as CBC, white blood cell differential, blood chemistry levels, or muscle enzyme levels)
• CT scan of the head or spine
• MRI of the head or spine
• Muscle or nerve biopsy
• Myelography
• Nerve conduction studies and electromyography   

Intravenous feeding or feeding tubes may be required in severe cases. Physical therapy, occupational therapy, or speech therapy may be recommended.

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

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

Mammen AL, Amato A. Statin myopathy: a review of recent progress. Curr Opin Rheum. 2010;22:644-650.