Weakness; Types, Causes, Symptoms, Diagnosis, Treatment

Weakness; Types, Causes, Symptoms, Diagnosis, Treatment

Weakness or asthenia is a symptom of a number of different conditions.The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis.

Spinal Cord Anatomy

Dorsal Column – Medial Lemniscus (fine touch, proprioception)

  • Afferent sensory fibers with cell body in DRG
  • Ascend in ipsilateral posterior column
  • Synapse in medulla, decussate, ascend in contralateral medial lemniscus
  • Synapse in thalamus (VPL)
  • Synapse in sensory strip of post-central gyrus

Spinothalamic Tract (pain, temperature)

  • Afferent sensory fibers with cell body in DRG
  • Ascends 1-2 levels
  • Synapse in ipsilateral spinal cord, decussate, ascend in contralateral lateral spinothalamic tract\
  • Synapse in thalamus (VPL)
  • Synapse in sensory strip of post-central gyrus

Lateral Corticospinal Tract (motor)

  • Efferent cell body in motor strip of pre-central gyrus
  • Descends through internal capsule
  • Decussates in pyramid of medulla, descends in contralateral lateral corticospinal tract
  • Synapse in anterior horn, lower motor neuron to muscle fiber


Muscle fatigue can be central, neuromuscular, or peripheral muscular. Central muscle fatigue manifests as an overall sense of energy deprivation, and peripheral muscle weakness manifests as a local, muscle-specific inability to do work. Neuromuscular fatigue can be either central or peripheral.

Central weakness

The central fatigue is generally described in terms of a reduction in the neural drive or nerve-based motor command to working muscles that results in a decline in the force output.It has been suggested that the reduced neural drive during exercise may be a protective mechanism to prevent organ failure if the work was continued at the same intensity.The exact mechanisms of central fatigue are unknown, though there has been a great deal of interest in the role of serotonergic pathways.

Neuromuscular weakness

Nerves control the contraction of muscles by determining the number, sequence, and force of muscular contraction. When a nerve experiences synaptic fatigue it becomes unable to stimulate the muscle that it innervates. Most movements require a force far below what a muscle could potentially generate, and barring pathology, neuromuscular fatigue is seldom an issue

Peripheral muscle weakness

Peripheral muscle fatigue during physical work is considered an inability for the body to supply sufficient energy or other metabolites to the contracting muscles to meet the increased energy demand. This is the most common case of physical fatigue—affecting a national average of 72% of adults in the work force in 2002. This causes contractile dysfunction that manifests in the eventual reduction or lack of ability of a single muscle or local group of muscles to do work.

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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 (MS)

Weakness may be caused by diseases or conditions affecting many different body systems, such as the following:

  • Adrenal glands not producing enough hormones (Addison disease)
  • Parathyroid glands producing too much parathyroid hormone (hyperparathyroidism)
  • Low sodium or potassium
  • Overactive thyroid (thyrotoxicosis)
  • Disease of the nerve cells in the brain and spinal cord (amyotrophic lateral sclerosis; ALS)
  • Weakness of the muscles of the face (Bell palsy)
  • Group of disorders involving brain and nervous system functions (cerebral palsy)
  • Nerve inflammation causing muscle weakness (Guillain-Barre syndrome)
  • Multiple sclerosis
  • Pinched nerve (for example, caused by a slipped disk in the spine)
  • Stroke
  • Botulism
  • Poisoning (insecticides, nerve gas)
  • Shellfish poisoning
  • Not enough healthy red blood cells (anemia)
  • Disorder of the muscles and nerves that control them (myasthenia gravis)
  • Polio
  • Electrolyte Imbalances
  • Malignant Tumors
  • Malnutrition
  • Muscle Disease Medications
  • Muscular Dystrophy
  • Myotonic Dystrophy
  • Nerve Impingement
  • Poisoning (Organophosphates)
  • Poliomyelitis
  • Thyrotoxicosis
  • Trauma
Non-neurological Shock (VS, clinical assessment)
Hypoglycemia (POC glucose)
Electrolyte derangement (BMP)
Anemia (POC Hb, CBC)
MI (ECG, troponin)
CNS depression (Utox, EtOH)
Cortex Stroke Tumor
Brainstem Stroke Demyelination
Spinal Cord Ischemia
Compression (disk, abscess, hematoma)
Demyelination (transverse myelitis)
Peripheral Acute demyelination (GBS) Compressive plexopathy
Muscle Rhabdomyolysis Inflammatory myositis


  • Slow or delayed movement in performing specific task.
  • Muscle cramps
  • Episodes of tremors or shaking while doing any task.
  • Muscle twitching.
  • Fever may be a common sign of asthenia affecting whole body.
  • Tiredness, loss or reduced energy is a common sign and symptom of asthenia.
  • Physical discomfort, loss or absence of muscle strength is also a symptom of asthenia.
  • Inability to finish a task or a movement.
  • Change in mental state or sometimes confusion.
  • Sudden change or reduced vision
  • Sudden loss of consciousness
  • Difficulty in speech, difficulty swallowing etc.

Weakness over all syndromes 

Unilateral weakness, ipsilateral face
  • Lesion: Contralateral cortex, internal capsule
  • Causes: Stroke (sudden onset), demyelination/mass (gradual onset)
  • Symptoms: Neglect, visual field cut, aphasia
  • Findings: UMN signs
  • Key features: Association with headache suggests hemorrhage or mass
Unilateral weakness, contralateral face
  • Lesion: Brainstem
  • Causes: Vertebrobasilar insufficiency, demyelination
  • Symptoms: Dysphagia, dysarthria, diplopia, vertigo, nausea/vomiting
  • Findings: CN involvement, cerebellar abnormalities
Unilateral weakness, no facial involvement
  • Lesion: Contralateral medial cerebral cortex, discrete internal capsule
  • Causes: Stroke
  • Rare Cause: Brown-Sequard if contralateral hemibody pain and temperature sensory disturbance
Unilateral weakness single limb (monoparesis/plegia)
  • Lesion: Spinal cord, peripheral nerve, NMJ
  • UMN signs: Brown-Sequard if contralateral pain and temperature sensory disturbance
  • LMN signs: Radiculopathy if associated sensory disturbance
  • Normal reflexes, normal sensation: Consider NMJ disorder
Bilateral weakness of lower extremities (paraparesis/plegia)
  • Lesion: Spinal cord, peripheral nerve
  • UMN signs: Anterior cord syndrome (compression, ischemia, demyelination) if contralateral pain and temperature sensory disturbance
  • Cauda equina: Loss of perianal sensation, loss of rectal tone, or urinary retentionGBS: If no signs of cauda equina and sensory disturbances paralleling ascending weakness (with hyporeflexia)
Bilateral weakness of upper extremities
  • Lesion: Central cord syndrome
  • Causes: Syringomyelia, hyperextension injury
  • Findings: Pain and temperature sensory disturbances in upper extremities (intact proprioception)
Bilateral weakness of all four extremities (quadriparesis/plegia)
  • Lesion: Cervical spinal cord
  • Findings: UMN signs below level of injury, strength/sensory testing identifies level
Bilateral weakness, proximal groups
  • Lesion: Muscle
  • Causes: Rhabdomyolysis, polymyositis, dermatomyositis, myopathies
  • Findings: Muscle tenderness to palpation, no UMN signs, no sensory disturbances
Facial weakness, upper and lower face
  • Lesion: CNVII
  • Causes: Bell’s palsy, mastoiditis, parotitis
  • Other CN involvement suggests brainstem lesion, multiple cranial neuropathies, or NMJ.
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Other testing is done based on where doctors think the problem is:

  • A brain disorder: Magnetic resonance imaging (MRI) or, if MRI is not possible, computed tomography (CT)

  • A spinal cord disorder: MRI or, when MRI is not possible, CT myelography and sometimes a spinal tap (lumbar puncture)

  • A peripheral nerve disorder (including polyneuropathies) or a neuromuscular junction disorder: Electromyography and usually nerve conduction studies

  • A muscle disorder (myopathy): Electromyography, usually nerve conduction studies, and possibly MRI, measurement of muscle enzymes, muscle biopsy, and/or genetic testing.

  • For CT myelography, CT is done after a needle is inserted into the lower back to inject a radiopaque dye into the fluid that surrounds the spinal cord.
  • For electromyography, a small needle is inserted into a muscle to record its electrical activity when the muscle is at rest and when it is contracting.
  • Nerve conduction studies use electrodes or small needles to stimulate a nerve. Then doctors measure how fast the nerve transmits signals.
  • A complete blood cell count (CBC)
  • Measurement of levels of electrolytes (such as potassium, calcium, and magnesium), sugar (glucose), and thyroid-stimulating hormone
  • Erythrocyte sedimentation rate (ESR), which can detect inflammation

  • Blood tests are sometimes done to evaluate kidney and liver function and to check for the hepatitis virus.
  • Magnetic Resonance Imaging (MRI) – A diagnostic procedure that uses a combination of large magnets, radio frequencies and a computer to produce detailed images of organs and structures within the body. This test is done to rule out any associated abnormalities of the spinal cord and nerves
  • Computerized Tomography Scan (also called a CT or CAT scan) – A diagnostic imaging procedure that uses a
  • combination of X-rays and computer technology to produce cross-sectional images (often called “slices”), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat and organs. CT scans are more detailed than general X-rays
  • EEG (electroencephalogram) – a test that measures the electrical activity in the brain, called brain waves. An EEG measures brain waves through small button electrodes that are placed on your child’s scalp
  • Spinal tap – also called lumbar puncture, a spinal tap is done to measure the amount of pressure in the spinal canal and/or to remove a small amount of cerebral spinal fluid (CSF) for testing. Cerebral spinal fluid is the fluid that bathes your child’s brain and spinal cord
  • Karyotype – This test, a chromosomal analysis from a blood test, is used to determine whether the problem is the result of a genetic disorder
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