Medical Health Encyclopedia

Weakness

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Weakness

Definition:

Weakness is a reduction in the strength of one or more muscles.

Alternative Names:
Lack of strength; Muscle weakness

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Considerations:

Weakness may be subjective (the person feels weak, but has no measurable loss of strength) or objective (measurable loss of strength as noted in a physical exam). Weakness may be generalized (total body weakness) or localized to a specific area, side of the body, limb, or muscle.

A subjective feeling of weakness may be associated with infectious diseases such as infectious mononucleosis and influenza.

Weakness is more notable when it occurs in only one area of the body (localized or focal weakness). Localized weakness may follow a stroke, exacerbation of multiple sclerosis, or trauma to a motor nerve root or peripheral nerve.

Common Causes:

Measurable weakness may result from a variety of conditions including metabolic, neurologic, primary muscular diseases, and toxic disorders.

METABOLIC

• Addison's disease
• Thyrotoxicosis

• Stroke (often localized weakness)
• Bell's palsy (weakness of one side of the face)
• A nerve impingement syndrome such as a slipped disk in the spine
• Multiple sclerosis (may be localized)
• Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease; often begins localized, gradually progressing to generalized)
• Cerebral palsy (localized weakness associated with spasticity)
• Guillain-Barre syndrome

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

TOXIC

• Organophosphate poisoning (insecticides, nerve gas)
• Paralytic shellfish poisoning
• Botulism

• Myasthenia gravis (an autoimmune disorder that interferes with the transmission of nerve impulses to muscle)
• Poliomyelitis ("polio" -- an infectious disease that damages motor neurons)

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