Weakness is reduced strength in one or more muscles.
Weakness may be all over the body or in only one area. 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
You may feel weak but have no real loss of strength. This is called subjective weakness. It may be due to an infection such as mononucleosis or the flu. Or, you may have a loss of strength that can be noted on a physical exam. This is called objective weakness.
Weakness may be caused by diseases or conditions affecting many different body systems, such as the following:
BRAIN/NERVOUS SYSTEM (NEUROLOGIC)
- Amyotrophic lateral sclerosis (ALS)
- Bell palsy
- Cerebral palsy
- Guillain-Barre syndrome
- Multiple sclerosis
- Pinched nerve (for example, caused by a slipped disk in the spine)
Follow the therapy your health care provider recommends to treat the cause of the weakness.
When to Contact a Medical Professional
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 being ill with a virus
- Weakness that does not go away and has no cause you can explain
- Weakness in one area of the body
What to Expect at Your Office Visit
The health care provider will do a physical exam. Your provider will also ask you about your weakness, such as when it began, how long it has lasted, and whether you have it all the time or only at certain times. You may also be asked about medicines you take or if you have been ill recently.
The health care provider may pay close attention to your heart, lungs, and thyroid gland. The exam will focus on the nerves and muscles if the weakness is only in one area.
You may have blood or urine tests. Imaging tests such as x-ray or ultrasound may also be ordered.
Lack of strength; Muscle weakness
Preston DC, Shapiro BE. Proximal, distal, and generalized weakness. In: Daroff RB, Fenichel GM, Jankovic J, Mazziota JC, eds. Bradley's Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 25.
Warner WC, Sawyer JR. Neuromuscular disorders. In: Canale ST, Beaty JH, eds. Campbell's Operative Orthopaedics. Philadelphia, PA: Mosby Elsevier; 2012:chap 35.
Review Date 8/17/2014
Updated by: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.