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

Spinothalamic Tract (pain, temperature)

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

Lateral Corticospinal Tract (motor)

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

Types

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

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 of the body to supply sufficient energy or other metabolites to the contracting muscles to meet the increased energy demand. This is the most common cause of physical fatigue—affecting a national average of 72% of adults in the workforce 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.

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 an 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:

METABOLIC

• Adrenal glands not producing enough hormones (Addison disease)
• Parathyroid glands produce too much parathyroid hormone (hyperparathyroidism)
• Low sodium or potassium
• Overactive thyroid (thyrotoxicosis)

BRAIN/NERVOUS SYSTEM (NEUROLOGIC)

• 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
• A pinched nerve (for example, caused by a slipped disk in the spine)
• Stroke

MUSCLE DISEASES

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

POISONING

• Botulism
• Poisoning (insecticides, nerve gas)
• Shellfish poisoning

OTHERS

• 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

LESION	CRITICAL	EMERGENT
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 Abscess Demyelination
Brainstem	Stroke	Demyelination
Spinal Cord	Ischemia Compression (disk, abscess, hematoma)	Demyelination (transverse myelitis)
Peripheral	Acute demyelination (GBS)	Compressive plexopathy
Muscle	Rhabdomyolysis	Inflammatory myositis

 Symptoms 

• Slow or delayed movement in performing specific tasks.
• Muscle cramps
• Episodes of tremors or shaking while doing any task.
• Muscle twitching.
• Fever may be a common sign of asthenia affecting the 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 in single limb (mono paresis/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 retention GBS: 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 the level of injury, strength/sensory testing identifies the 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: CN VII
• Causes: Bell’s palsy, mastoiditis, parotitis
• Other CN involvement suggests brainstem lesions, multiple cranial neuropathies, or NMJ.

Diagnosis