Muscle Weakness (Paresis) : Causes, Symptoms, Diagnosis & Treatment

Last Updated: 19/09/2022

Muscle weakness is an objective symptom, expressed as a decrease in skeletal muscle strength, or a subjective sensation, described as increased fatigue. The reasons for this phenomenon are extremely diverse and usually include structural damage at any level of signal transmission along the nerve pathways, damage to myoneural synapses, and muscle fibers. Diagnosis is carried out by means of neuroimaging, neurophysiological procedures, laboratory methods. Treatment involves conservative and surgical correction.

Muscle weakness and muscle fatigue are some of the most common symptoms that people seek neurological care for. There are objective and subjective criteria to determine the presence of a pathological condition. When speaking of weakness, they usually mean a decrease in muscle strength, but patients often complain of general fatigue or difficulty in moving in certain areas of the body.

Weakness can be present in individual muscles, affect many groups, or the entire body. It occurs suddenly or increases gradually, is noted periodically or persists constantly. In the paretic limbs, muscle tone changes, reflexes are revived or weakened. Depending on the origin and localization of the pathological focus, the clinical picture is supplemented by other symptoms.


Weakness in the muscles is due to a wide range of pathologies. It can be general (common) or local. The first implies a state of increased fatigue while maintaining muscle strength. In the second case, a violation of the pathways for conducting a nerve impulse from the central nervous system to certain muscles is ascertained. At the same time, for topical diagnosis, it is important to understand the level of damage:

  • Central motor neuron: motor cortex, corticospinal and corticobulbar tracts.
  • Peripheral motor neuron: anterior horns of the spinal cord, roots, nerves.
  • neuromuscular synapse.
  • Muscles.

If the central or peripheral motor neurons are involved, paresis with a decrease in muscle strength is noted. According to the degree of severity, they are mild, moderate, deep, or take on the character of paralysis (complete lack of movement). Traditionally, paresis is systematized taking into account the localization of the lesion and clinical features. In neurology, the following classification is generally accepted:

  • Central (spastic). By eliminating the inhibitory effect of the cortex on the spinal cord, muscle tone and reflexes increase, pathological signs and synkinesis appear.
  • Peripheral (sluggish). The defeat of the peripheral motor neuron leads to a rupture of the reflex arc, which is accompanied by hypotension and hyporeflexia, muscle atrophy, fascicular twitching are noticeable on examination.
  • Mixed. The combination of spastic paresis below the level of the lesion due to interruption of the corticospinal tract and peripheral, due to the pathological process in the region of the anterior cords of the spinal cord.

Separately, psychogenic paresis is distinguished, which occur without organic causes with the complete preservation of the pathways of the brain and spinal cord. Their development is associated with a violation of the functions of higher nervous activity. The involvement of individual limbs in the process is essential for diagnosis, therefore, several types of paresis are distinguished in the clinic of nervous diseases:

  • Monoparesis. Weakness is observed in one limb.
  • Biparesis. It is divided into hemiparesis, in which the arm and leg on one side suffer, and paraparesis with the involvement of symmetrical limbs - upper or lower.
  • Triparesis. Muscle strength is reduced in three limbs (combination of hemi- and paraparesis).
  • Tetraparesis. Movement disorders cover both arms and legs.

Based on the prevalence, weakness of some muscles (for example, fingers or facial expressions), entire groups (flexors, extensors) or departments (distal, proximal) are isolated. It should be understood that the term "paresis" is used not only to describe the work of skeletal muscles, but also applies to some internal organs (intestines, bladder).


Why Muscle Weakness Occurs

Causes of weakness in the limbs

Considering the origin of skeletal muscle weakness, it is worth dividing the concept of paresis associated with damage to the nerve pathways and symptoms caused by defects in synaptic transmission, muscle damage. Often we are talking about the blockade or increased destruction of acetylcholine, primary or secondary muscle pathology, reflex syndromes. Among the most well-known causes of weakness are the following:

  • Myasthenia.
  • Myasthenic syndromes: Lambert-Eaton associated with slow closure of ion channels, familial infantile myasthenia gravis.
  • Hereditary paroxysmal myoplegia: hyper-, hypo- and normokalemicheskaya, Andersen-Tavila syndrome.
  • Infections: botulism, tick-borne encephalitis.
  • Endocrine pathology: hyper- and hypothyroidism, Conn's syndrome, Addison's disease.
  • Myopathies: inflammatory (acute myositis, polymyositis, dermatomyositis), metabolic (including storage diseases), mitochondrial.
  • Muscular dystrophies: progressive (Duchenne, Becker, Emery-Dreyfus), non-progressive (myotubular myopathy).
  • Diseases of the musculoskeletal system: arthrosis, tendonitis, trauma.
  • Vascular pathology: obliterating endarteritis, varicose veins of the lower extremities, Takayasu's disease.
  • Poisoning: organophosphorus compounds, carbon monoxide, cyanides, aromatic hydrocarbons (toluene, benzene), plants (hemlock), nicotine, cocaine.
  • Taking medications: D-penicillamine, antibiotics, anticancer drugs, statins, cortisone, colchicine, chloroquine.

Weakness in the muscles of the whole body is provoked by various systemic diseases, intoxications. It is noted in acute and chronic infections, autoimmune pathology, malignant tumors. Low motor activity in the elderly, with immobilization, prolonged bed rest are common causes of widespread limb weakness.

Causes of weakness of the facial muscles

Mimic muscles are innervated by the facial nerve (VII pair). Any pathology that disrupts the conduction of an impulse along the motor fibers - from the corticonuclear pathway to the peripheral section - can cause muscle weakness. It is also worth considering the direct damage to the muscles themselves. The list of possible pathologies includes the following conditions:

  • Neuritis of the facial nerve (Bell's palsy).
  • Facial-shoulder myodystrophy of Landouzy-Dejerine.
  • Degenerative diseases: progressive bulbar palsy, syringobulbia.
  • Tumors: base of the skull (Garsin's syndrome), cerebellopontine angle, temporal bone and middle ear.
  • Hemorrhages and infarctions of the region of the pons.
  • Congenital anomalies: Chiari malformation, Klippel-Feil syndrome.
  • Infections: herpetic ganglionitis of the geniculate ganglion (Ramsey-Hunt syndrome), polioencephalitis, Lyme disease, syphilis.
  • Meningitis: bacterial, tuberculous, fungal.
  • Systemic pathology: sarcoidosis, periarteritis nodosa, Behçet's disease.
  • Consequences of traumas, operations on the face, installation of a cochlear implant.
  • Action of chemotherapy drugs.

The facial nerve is often damaged during inflammatory processes in the ear and parotid salivary gland. Compression or rupture of its fibers is observed in TBI with a fracture of the base of the skull. The risk of paresis of the facial nerve increases in the elderly, with a long history of smoking, the presence of concomitant pathology (diabetes mellitus, arterial hypertension).

Causes of paresis

The upper or first neuron of the motor pathway begins in the motor cortex of the precentral gyrus, goes as part of the pyramidal tract through the internal capsule and trunk, ending in the anterior horns of the spinal cord. There, the impulse is transmitted to the second motor neuron, the axons of which make up the roots and peripheral nerves. Damage to these structures at any length is accompanied by paresis, which is typical for various pathologies of the nervous system:

  • Strokes: hemorrhagic, ischemic, subarachnoid hemorrhage.
  • Tumors and traumatic brain injury.
  • Demyelinating diseases: leukodystrophy, multiple sclerosis, Devic optomyelitis.
  • Motor neuron diseases: amyotrophic lateral sclerosis, spinocerebellar and bulbospinal atrophy.
  • Cerebral palsy.
  • Neurodegenerative processes: Wilson-Konovalov, Strümpel, Refsum disease.
  • Myelopathy: compression, ischemia of the spinal cord, transverse myelitis.
  • Damage to peripheral nerves: polyneuropathies (metabolic, toxic, hereditary), tunnel syndromes, plexopathies.
  • Acute polyradiculoneuritis: diphtheria, Guillain-Barré syndrome, Landry's ascending paralysis.
  • Infections: poliomyelitis, meningococcal meningoencephalitis, rabies.
  • Vertebrogenic pathology: intervertebral hernia, osteochondrosis, scoliosis.
  • Intoxication: nerve poisons, salts of heavy metals (thallium, lead, arsenic).

Violation of spinal conduction is often caused by spinal cord injuries, which entail compression, ischemic damage, and swelling of the nervous tissue. There are also direct wounds - gunshot, bone fragments in fractures. Usually, the cervical region is affected by such injuries, the thoracic and lumbar are affected much less frequently. With a concussion of the brain tissue, the changes are transient, in other cases they are more persistent.

Metastatic tumors (with cancer of the lung, breast or prostate) become a common cause of compression of the spinal cord, less often lymphoma, multiple myeloma, epidural hematomas are diagnosed. If weakness appears in the arms or legs, tuberculous spondylitis, rheumatoid arthritis with subluxation of the atlantoaxial joint, and spinal vascular malformations are excluded.


When conducting a clinical examination, true weakness in the muscles with a decrease in strength is distinguished from increased fatigue as a subjective sign. In the anamnesis, they find out information about the intensity and rate of development of the symptom, the presence of additional signs. During a neurological examination, the doctor determines muscle strength (in points), the volume of active and passive movements, reflexes. To determine the cause of muscle weakness, additional studies are prescribed:

  • Blood analysis. If an infection is suspected, the hemogram gives an idea of ​​the leukocyte formula, ESR. Biochemical analysis reveals electrolyte and hormonal disorders, the presence of antibodies to the pathogen. Toxicological examination shows the content of toxic substances in the blood.
  • Lumbar puncture. Cerebrospinal fluid is taken for examination to exclude subarachnoid hemorrhages, infectious and inflammatory diseases of the brain and membranes. The pressure of the cerebrospinal fluid is evaluated during volumetric processes (tumors, abscesses, hematomas).
  • Radiography. X-ray of the spine is the first study prescribed for spinal injuries. Standard x-rays do not show fractures of the odontoid process or lower cervical segment, which requires the appointment of special radiographs and the use of other imaging techniques.
  • Tomography. In CNS lesions, MRI is considered the main method of neuroimaging. The method is highly informative in the pathology of the posterior cranial fossa, inflammation of the meninges, myelopathy. CT of the brain is more suitable for patients with fractures of the base of the skull, in the acute period of a stroke.
  • Myelography. It is an x-ray study of the central canal of the spinal cord. The procedure is performed for herniated intervertebral discs, spinal injuries, tumors. The technique shows any obstacles to normal liquorodynamics.
  • Electroneuromyography. The defeat of the nerve trunks and fibers requires a functional study with an analysis of the conduction of the impulse to the muscles, which makes it possible to assess the speed of the signal, the location of the damage, and the ability of the muscles to contract.

If muscle weakness is accompanied by systemic disorders, the examination plan includes ultrasound of the kidneys and adrenal glands, thyroid and parathyroid glands. With vascular disorders, ultrasound, angiography are done. The search for a malignant tumor may require radioisotope scintigraphy. Given the variety of causes, a neurologist has to carry out a thorough differential diagnosis with the involvement of related specialists.

In the complex treatment of paresis, therapeutic ficulture is used


Treatment of paresis

Help before diagnosis

A sudden pronounced local or general weakness of the muscles is the reason for seeking medical help. In acute conditions associated with a direct threat to life, urgent measures are needed. Suspicion of craniocerebral and spinal injuries requires immobilization of the cervical region with a head holder or collar, patients with probable spinal injury are transported on a rigid stretcher.

In case of serious injuries with paresis of the respiratory muscles, hemorrhagic stroke, resuscitation measures are necessary - mechanical ventilation with intubation, chest compressions. At the prehospital stage, blood pressure is stabilized, cerebral edema is controlled, vomiting and convulsions are stopped. The undifferentiated treatment of stroke involves the use of neuroprotectors.

Conservative therapy

A decrease in muscle strength requires a comprehensive solution aimed at eliminating the cause of motor dysfunction and restoring lost abilities. The basis of a conservative strategy is drug therapy, selected in accordance with clinical expediency. Given the causes and mechanisms for the development of weakness, the following drugs can be prescribed:

  • Neuroprotectors. They are used for strokes (ischemic, hemorrhagic), the consequences of TBI, myelopathy. The main directions of neuroprotection are represented by antioxidant protection, inhibition of local inflammation (antagonists of cytokines), improvement of trophism (nootropics, choline, carnitine preparations), blood circulation (nimodipine, vinpocetine).
  • Immunosuppressors. Myasthenia gravis is treated with immunosuppressants (azathioprine, cyclosporine), immunoglobulins. Interferons, monoclonal antibodies, glucocorticoids are used to suppress autoimmune reactions in patients with multiple sclerosis. The latter are also used as replacement therapy for Addison's disease, with cerebral edema, and radicular syndrome.
  • Antimicrobial. Therapy of neuroinfections of bacterial origin requires the appointment of antibiotics. With tick-borne encephalitis, specific immunoglobulins are indicated, botulism is treated with the introduction of antitoxic serum. In addition to etiotropic therapy for acute infections, detoxification agents are prescribed.

Correction of metabolic disorders is required for endocrine pathology, some myopathies, polyneuropathies. Actively use B vitamins, NSAIDs, cholinesterase inhibitors. The treatment regimen for vascular pathology includes vasoactive agents (pentoxifylline), venotonics, and antiplatelet agents. Poisoning is treated with active detoxification, including using extracorporeal methods.

At the stage of rehabilitation, non-drug correction plays a special role. Massage, exercise therapy contribute to the restoration of muscle strength and range of motion. Therapeutic-activating regimens depend on the patient's condition and the time that has passed since the cerebral injury. In the complex treatment of paresis, kinesiotherapy, physiotherapy, and orthopedic correction are used.


Surgery is often required to repair the structural defects that caused the paresis. In ischemic stroke, reperfusion techniques are recommended: selective thrombolysis, shunting, endarterectomy. Hemorrhages are removed by puncture-aspiration, stereotaxic, microsurgical methods. With compression of the spinal roots, some neuropathies, tunnel syndromes, decompression operations are necessary.

With the ineffectiveness of conservative therapy for myasthenia gravis, it is recommended to remove the thymus gland (thymectomy), which reduces autoimmune aggression. In case of post-traumatic and postoperative paresis of the facial nerve, reconstructive interventions (suturing, autoplasty) and plastic surgeries (lifting, muscle repositioning) are performed to improve the aesthetic result.

Experimental treatment

Therapy for many diseases manifested by muscle weakness continues to improve. Clinical trials have shown the effectiveness of gene therapy for stroke, spinal muscular atrophy. There is evidence of the effectiveness of the treatment of myasthenia gravis with rituximab, with multiple sclerosis, it is proposed to use low doses of naltrexone. In the process of restoring motor function, transplantation of mesenchymal stem cells looks promising.

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