Muscle twitches are fine movements of a small area of muscle.

Muscle fasciculation; Fasciculations of muscle

Muscle twitching is caused by minor muscle contractions in the area, or uncontrollable twitching of a muscle group that is served by a single motor nerve fiber.

Muscle twitches are minor and often go unnoticed. Some are common and normal. Others are signs of a nervous system disorder.

• Autoimmune disorders such as Isaac syndrome
• Drug overdose (caffeine, amphetamines, or other stimulants)
• Drug side effect (such as from diuretics, corticosteroids, or estrogens)
• Exercise
• Lack of nutrients in the diet (deficiency)
• Stress
• Twitches not caused by disease or disorders (benign twitches)
  • Often affecting the eyelids, calf, or thumb
  • Normal and quite common, often triggered by stress or anxiety
  • Come and go, and do not last for more than a few days

Nervous system conditions that can cause muscle twitching:

• Amyotrophic lateral sclerosis (ALS - Lou Gehrig's disease)
• Damage to the nerve that leads to a muscle
• Muscular dystrophy
• Spinal muscular atrophy
• Weak muscles (myopathy)

Symptoms of a nervous system disorder include:

• Loss of, or change in, sensation
• Loss of muscle size (wasting)
• Weakness

No treatment is usually needed for benign muscle twitching.

Call your health care provider if you have long-term or persistent muscle twitches.

Your health care provider will take a medical history and perform a physical examination.

Medical history questions may include:

• When did you first notice the twitching?
• How long does it last?
• How often do you experience twitching?
• What muscles are affected?
• Is it always in the same location?
• Are you pregnant?
• What other symptoms do you have?

Tests depend on the suspected cause, and may include:

• Blood tests to look for problems with electrolytes, thyroid gland function, and blood chemistryCT scan of the spine or brain
• Electromyogram (EMG)
• Nerve conduction studies
• MRI scan of the spine or brain

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.