Upper and Lower Motor Neuron Lesions

Upper motor neurons (UMNs) and lower motor neurons (LMNs) combine to form a neuronal circuit for movement. UMNs are responsible for carrying motor information from the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex and brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem to the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord, and LMNs carry motor information from UMNs in the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord to the skeletal muscles for movement. Upper motor neuron lesions cause damage to neurons above the motor nuclei of the cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem or the anterior horn cells in the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord. These lesions present clinically with symptoms of weakness, spasticity, clonus, and hyperreflexia. Causes include stroke, traumatic brain injury, brain cancer, infectious and inflammatory disorders, and metabolic and neurodegenerative disorders. Lower motor neuron lesions affect the nerve fibers traveling from the anterior horn of the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord to the peripheral muscle. These lesions present clinically with muscle weakness, atrophy, and hyporeflexia, with sensation remaining intact. Diagnosis is made by clinical neurologic exam, and management is mostly supportive, but some newer therapies have recently become available.

Last update:

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp

Overview

Definition

Upper motor neuron (UMN) lesions originate in the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex or brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem and cause damage to neurons above the motor nuclei of the cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves (CNs) in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem or the anterior horn cells in the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord (SC).
Lower motor neuron (LMN) lesions affect the nerve fibers traveling from the anterior horn of the SC to the peripheral muscle.

Anatomy and physiology

  • CNS controls the skeletal muscles via 2 types of motor neurons:
    • UMNs: further divided into pyramidal and extrapyramidal tracts
    • LMNs 
  • UMN pyramidal tract:
    • Direct pathway between cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex and SC
    • Carries signals for voluntary movements only
    • Motor areas of the cerebral hemispheres innervate muscles on the contralateral side of the body.
    • Divided into:
      • Corticospinal tract (whose fibers synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission with spinal nerves)
      • Corticobulbar tract (whose fibers synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission with CNs in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem
  • UMN extrapyramidal tract:
    • Indirect connection:  fibers pass through the tegmentum rather than the medullary pyramid
    • Involved in:
      • Initiation and coordination of voluntary movements
      • Involuntary movements such as reflexes (pyramidal system controls voluntary movements only)
  • LMNs: 
    • Found in the anterior horn/ventral SC or at the CN nuclei in the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem
    • Exist in both the central and peripheral nervous systems
    • Classification:
      • Branchial muscles innervated by CNs V, VII, IX, and X
      • Visceral: autonomic sympathetic (fight-or-flight response) and parasympathetic (rest and digest) innervation to the smooth muscles, glands, and GI tract
      • Lower motor neurons do not directly innervate the viscera but contribute to the CN functions that regulate these responses.
      • Somatic: directly innervate skeletal muscles for contraction/movement

Etiologies of motor neuron lesions

  • Hereditary
    • UMN: hereditary spastic paraplegia 
    • LMN: 
      • Spinal muscular atrophy Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA) ( SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA))
      • Distal hereditary motor neuropathies 
  • Sporadic 
    • UMN: 
      • Primary lateral sclerosis
      • Ischemic stroke Ischemic Stroke An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke
      • Spinal cord transection
      • Brown-Séquard syndrome Brown-Séquard syndrome Brown-Séquard syndrome (BSS) is a rare neurologic injury that causes hemisection of the spinal cord, resulting in weakness and paralysis of one side of the body and sensory loss on the opposite side. Brown-Séquard Syndrome 
    • LMN: poliomyelitis Poliomyelitis Poliomyelitis is an infectious disease caused by the poliovirus. Transmission occurs through the fecal-oral route and through respiratory aerosols. The majority of patients will be asymptomatic or have a mild, abortive presentation with flu-like symptoms. Those who develop nonparalytic poliomyelitis will develop signs and symptoms of aseptic meningitis. A very minor proportion of patients will progress to paralytic poliomyelitis. Poliovirus/Poliomyelitis 
    • Both UMN and LMN: 
      • Lesions secondary to trauma 
      • Compression from malignancy
  • Immune-mediated 
    • UMN: none
    • LMN: 
      • Multifocal motor neuropathy
      • Chronic inflammatory demyelinating polyneuropathy Polyneuropathy Polyneuropathy is any disease process affecting the function of or causing damage to multiple nerves of the peripheral nervous system. There are numerous etiologies of polyneuropathy, most of which are systemic and the most common of which is diabetic neuropathy. Polyneuropathy (CIDP)
      • Guillain-Barré syndrome Guillain-Barré syndrome Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Guillain-Barré Syndrome
Umn vs lmn lesions

Upper motor neuron (UMN) and lower motor neuron (LMN) pathways

Image by Lecturio.

Clinical Presentation

UMN lesions above the decussation manifest as motor symptoms on the same side of the body, whereas lesions below the pyramidal decussation present on the contralateral side of the body. Pathologic mechanisms of LMN lesions involve axonal degeneration and cell death Cell death Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects. Cell Injury and Death of the LMN.

Signs associated with upper motor neuron lesions

  • Weakness
  • Clonus
  • No fasciculations
  • Increased tone
    • Spasticity 
    • Clasp-knife rigidity 
  • Hyperreflexia
  • Positive Babinski sign: extension (dorsiflexion) of the big toe and fanning of the other toes
  • Pseudobulbar palsy:
    • Slurred speech
    • Dysphagia Dysphagia Dysphagia is the subjective sensation of difficulty swallowing. Symptoms can range from a complete inability to swallow, to the sensation of solids or liquids becoming "stuck." Dysphagia is classified as either oropharyngeal or esophageal, with esophageal dysphagia having 2 sub-types: functional and mechanical. Dysphagia
    • Dysarthria
    • Tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Oral Cavity: Lips and Tongue spasticity
    • Pseudobulbar affect: emotional manifestations, including uncontrollable episodes of crying, laughing, and anger

Signs associated with lower motor neuron lesions

  • Weakness
  • Atrophy
  • Fasciculations:
    • Visible, involuntary contractions of groups of motor units
    • Secondary to reinnervation of denervated fibers that spontaneously depolarize
  • Decreased tone
  • Hyporeflexia
  • Bulbar palsy: 
    • Symptoms related to impaired function of the lower CNs (IX, X, XI, and XII)
    • Involves impairment of muscles used for chewing, swallowing, and tongue movements

Summary of clinical findings in upper and lower motor neuron lesions

Table: Clinical findings that help differentiate upper motor neuron (UMN) from lower motor neuron (LMN) lesions
Clinical finding UMN lesion LMN lesion
Muscle tone Muscle tone The state of activity or tension of a muscle beyond that related to its physical properties, that is, its active resistance to stretch. In skeletal muscle, tonus is dependent upon efferent innervation. Skeletal Muscle Contraction
  • Spastic
  • Rigid
Hypotonic
Muscle mass No change Muscle wasting present
Fasciculation None Present
Tendon reflexes Hyperreflexia Hyporeflexia/areflexia
Electromyographic findings Normal nerve conduction Abnormal nerve conduction

Diagnosis

It is important to differentiate central from peripheral nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System lesions on exam.

History

  • Onset of disease 
  • Progression (rapid versus gradual)  
  • Symptoms as above

Physical exam

  • Muscle examination:
    • Muscle bulk: Inspect for atrophy seen with LMN lesions.
    • Muscle tone Muscle tone The state of activity or tension of a muscle beyond that related to its physical properties, that is, its active resistance to stretch. In skeletal muscle, tonus is dependent upon efferent innervation. Skeletal Muscle Contraction: Inspect for spasticity or rigidity seen with UMN lesions.
    • Inspect for fasciculations .
    • Test for symmetric versus asymmetric weakness.
    • Test for proximal (LMN/spinal nerves) versus distal (due to peripheral nerve lesions) weakness.
  • Complete neurologic exam:
    • Cranial nerves
    • Motor and sensory
    • Reflexes

Diagnostic tests Diagnostic tests Diagnostic tests are important aspects in making a diagnosis. Some of the most important epidemiological values of diagnostic tests include sensitivity and specificity, false positives and false negatives, positive and negative predictive values, likelihood ratios, and pre-test and post-test probabilities. Epidemiological Values of Diagnostic Tests

  • Electromyography (EMG): 
    • Abnormal electrical signals occur in the muscle affected by motor neuron lesions.
    • Detects spontaneous depolarization of denervated muscle fibers
  • Nerve conduction study
  • Lumbar puncture
  • Laboratory tests to rule out other causes:
    • Complete metabolic panel 
    • Serum vitamin B12 level
    • Copper level 
    • HIV antibody  
  • MRI imaging to evaluate for:
    • Brain and SC tumors
    • Stroke
    • Inflammatory disorders
    • Infectious brain or SC lesions
    • Multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis

Genetic tests

  • Used for identifying genes involved in some UMN and LMN syndromes:
    • Spinal muscular atrophy Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA)
    • Spinobulbar muscular atrophy 
    • Some causes of familial ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis
  • Includes next-generation sequencing:
    • A modern DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure-sequencing technology to study genetic variation associated with certain diseases 
    • Entire genome can be sequenced in 1 day.

Management

There is no standard treatment for motor neuron diseases, but there are some medical and surgical methods available to treat the sequelae of UMN and LMN lesions and help individuals maintain their quality of life.

Supportive management

  • Physical therapy:
    • Stretching and strengthening exercises to reduce stiffness
    • Prevent and treat contractures.
    • Help improve posture.
    • Prevent joint immobility.
    • Slow muscle weakness and atrophy.
  • Speech therapy:
    • Helps with chewing and swallowing difficulties
    • Speech synthesizers
  • Assistive devices:
    • Mobility aids AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS: canes, wheelchairs, motorized scooters
    • Braces, orthotics
  • Other therapies:
    • Feeding tubes may be required to maintain good nutrition.
    • Noninvasive positive pressure ventilation or assisted ventilation: for severe muscle weakness in the neck, throat, and chest

Medication

  • Muscle relaxers for spasticity:
    • Baclofen
    • Tizanidine
    • Dantrolene
    • Botulinum toxin injections: treat muscle stiffness by weakening overactive muscles
  • For excess salivation (antisialogogues):
    • Amitriptyline (a tricyclic antidepressant Antidepressant Antidepressants encompass several drug classes and are used to treat individuals with depression, anxiety, and psychiatric conditions, as well as those with chronic pain and symptoms of menopause. Antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), and many other drugs in a class of their own. Serotonin Reuptake Inhibitors and Similar Antidepressant Medications with anticholinergic Anticholinergic Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs properties causing dry mouth)
    • Glycopyrrolate
    • Atropine
    • Botulinum toxin injections into the salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands to stop drooling
  • Disease-specific medications:
    • ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis: New drugs available may provide protection against further damage to motor neurons and prevent disease progression.
    • Spinal muscular atrophy Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA): Some new gene therapies are available.
    • Multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis: immunomodulators and immunosuppressants Immunosuppressants Immunosuppressants are a class of drugs widely used in the management of autoimmune conditions and organ transplant rejection. The general effect is dampening of the immune response. Immunosuppressants

Surgery

  • If individual has voluntary control of extremities: can lengthen spastic muscles to increase the individual’s level of function
  • If individual is not able to use extremities: may need muscle origin release, myotomy, tenotomy, neurectomy, or arthrodesis

Clinical Relevance

Syndromes with upper motor neuron lesion features

  • Stroke: also known as a cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke. Stroke can be ischemic (cerebral blood vessel occlusion by thrombosis or embolism) or less commonly hemorrhagic (intracranial bleeding). The clinical presentation includes neurologic symptoms with varying degrees of motor and sensory loss corresponding to the area of the brain affected and the extent of the tissue damage. Diagnosis is made by physical examination and imaging. Management depends on whether it is a thrombotic or hemorrhagic event.
  • Brown-Séquard syndrome Brown-Séquard syndrome Brown-Séquard syndrome (BSS) is a rare neurologic injury that causes hemisection of the spinal cord, resulting in weakness and paralysis of one side of the body and sensory loss on the opposite side. Brown-Séquard Syndrome: refers to hemisection of the SC secondary to injury, most commonly from penetrating trauma. Other etiologies include blunt trauma, disc herniation, hematoma, and malignancy. The clinical presentation of Brown-Séquard syndrome Brown-Séquard syndrome Brown-Séquard syndrome (BSS) is a rare neurologic injury that causes hemisection of the spinal cord, resulting in weakness and paralysis of one side of the body and sensory loss on the opposite side. Brown-Séquard Syndrome is with weakness and paralysis of 1 side of the body and sensory loss on the opposite side. The UMN lesion syndrome manifests ipsilaterally and below the level of the hemisection.  
  • Primary lateral sclerosis (PLS): UMN neurodegenerative disorder. Primary lateral sclerosis is considered to be sporadic, although there are some subtypes with genetic heritability. The disorder presents similarly to ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis, although with slower progression and without any LMN findings initially. The majority of people with PLS will progress to ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis within 4 years of symptom onset. There is no cure for PLS, and management is supportive, similar to that for ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis
  • Hereditary spastic paraplegia (HSP): neurodegenerative disorder presenting with bilateral lower extremity weakness and spasticity. This disorder is a hereditary cause of UMN lesions. In addition to the UMN signs, HSP may present with cognitive impairment, ataxia, and peripheral neuropathy. Management is similar to that for ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis, but HSP has a better prognosis; progression of the disease is much slower and symptoms are usually limited to the lower extremities. 
  • Vitamin B12 deficiency: may arise because of insufficient intake, gastrectomy, and autoimmune destruction of gastric parietal cells, among others. This deficiency manifests clinically as fatigue and peripheral neuropathy and even has psychiatric features. The diagnosis is confirmed through megaloblastic anemia Megaloblastic anemia Megaloblastic anemia is a subset of macrocytic anemias that arises because of impaired nucleic acid synthesis in erythroid precursors. This impairment leads to ineffective RBC production and intramedullary hemolysis that is characterized by large cells with arrested nuclear maturation. The most common causes are vitamin B12 and folic acid deficiencies. Megaloblastic Anemia on CBC and measurement of serum B12 levels. Management is via removing barriers to absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption plus supplementation.

Syndromes with lower motor neuron lesion features

  • Poliomyelitis: infectious disease caused by poliovirus Poliovirus Poliomyelitis is an infectious disease caused by the poliovirus. This virus is a member of the Picornaviridae family. It is a small, single-stranded, positive-sense RNA virus without a lipid envelope. Transmission occurs through the fecal-oral route and, occasionally, through respiratory aerosols. Poliovirus/Poliomyelitis affecting the anterior horn cells via inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation. Transmission of poliomyelitis Poliomyelitis Poliomyelitis is an infectious disease caused by the poliovirus. Transmission occurs through the fecal-oral route and through respiratory aerosols. The majority of patients will be asymptomatic or have a mild, abortive presentation with flu-like symptoms. Those who develop nonparalytic poliomyelitis will develop signs and symptoms of aseptic meningitis. A very minor proportion of patients will progress to paralytic poliomyelitis. Poliovirus/Poliomyelitis occurs through the fecal–oral route and through respiratory aerosols. A very small proportion of individuals will progress to paralytic poliomyelitis Poliomyelitis Poliomyelitis is an infectious disease caused by the poliovirus. Transmission occurs through the fecal-oral route and through respiratory aerosols. The majority of patients will be asymptomatic or have a mild, abortive presentation with flu-like symptoms. Those who develop nonparalytic poliomyelitis will develop signs and symptoms of aseptic meningitis. A very minor proportion of patients will progress to paralytic poliomyelitis. Poliovirus/Poliomyelitis with neurologic progression. Diagnosis is by clinical presentation, viral culture, PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR), and serology. Current antivirals are ineffective, and management is supportive. The 2 available vaccines have almost eradicated this disease worldwide. 
  • Guillain-Barré syndrome Guillain-Barré syndrome Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Guillain-Barré Syndrome (GBS): immune-mediated neuropathy that may occur after a bacterial or viral infection or less frequently after a triggering event such as immunization or trauma. Guillain-Barré syndrome Guillain-Barré syndrome Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Guillain-Barré Syndrome is characterized by acute, symmetric, ascending neuromuscular paralysis that can progress to respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure. Diagnosis is based on clinical presentation, exam, and CSF findings. Management is mostly supportive and may require either plasma exchange or IV immunoglobulin. 
  • Spinal muscular atrophy Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA) ( SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA)): spectrum of autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritancesyndromes characterized by progressive proximal muscle weakness and atrophy. Spinal muscular atrophy Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA) is due to degeneration of the anterior horn cells in the SC and motor nuclei in the lower brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem. There are 5 clinical types of SMA SMA Spinal muscular atrophy (SMA) is a spectrum of autosomal recessive syndromes characterized by progressive proximal muscle weakness and atrophy, possibly due to degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem. Spinal Muscular Atrophy (SMA), each with its distinctive clinical presentation. Initial diagnosis is made clinically and confirmed with genetic testing. Management is mostly supportive, and the prognosis depends on the clinical type. 
  • Spinobulbar muscular atrophy (Kennedy disease): X-linked disorder of brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem and SC LMNs that classically presents in men ages 20–50 and worsens progressively over time. Manifestations of this disease are facial and limb-girdle muscle atrophy and weakness, tremor, fasciculations, mild cognitive impairment, and some associated endocrinopathies. Diagnosis is made with lab and genetic testing and also electromyography and nerve conduction velocity testing (EMG/NCV). Management is supportive.

Syndromes with both upper and lower motor neuron features

  • Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis ( ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis): also known as Lou Gehrig disease. Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis is a sporadic or inherited neurodegenerative disease of UMNs and LMNs. This disease is characterized by the coexistence of UMN and LMN signs and symptoms that lead to weakness and difficulty speaking and swallowing. The diagnosis is made clinically. Management is supportive and symptomatic, with a poor prognosis and low 5-year survival.
  • Multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis (MS): chronic inflammatory autoimmune disease leading to CNS demyelination. The clinical presentation of MS varies widely depending on the site of lesions, but it typically involves neurologic symptoms affecting vision, motor function, and autonomic function. The diagnosis is based on clinical findings, MRI imaging, and CSF examination. Management involves corticosteroids for acute exacerbations and disease-modifying agents.

References

  1. Emos, M.C., Agarwal, S. (2020). Neuroanatomy, upper motor neuron lesion. StatPearls. Retrieved August 8, 2021,  from https://www.ncbi.nlm.nih.gov/books/NBK537305/
  2. Javed, K., Daly, D.T. (2020). Neuroanatomy, lower motor neuron lesion. StatPearls. Retrieved August 8, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK539814/
  3. Fullam, T., Statland, J. (2021). Upper motor neuron disorders: primary lateral sclerosis, upper motor neuron dominant amyotrophic lateral sclerosis, and hereditary spastic paraplegia. Brain Sciences 11:611. https://doi.org/10.3390/brainsci11050611
  4. Garg, N., et al. (2017). Differentiating lower motor neuron syndromes. Journal of Neurology, Neurosurgery, and Psychiatry 88:474–483. https://pubmed.ncbi.nlm.nih.gov/28003344/
  5. Miller, M.L. (2021). Approach to the patient with muscle weakness. UpToDate. Retrieved August 18, 2021, from  https://www.uptodate.com/contents/approach-to-the-patient-with-muscle-weakness
  6. Zayia, L.C., Tadi, P. (2021). Neuroanatomy, motor neuron. StatPearls. Retrieved August 8, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK554616/
  7. Ratti, E. (2015). Motor Neuron Diseases. DeckerMed Medicine. Retrieved August 8, 2021. http://dx.doi.org/10.2310/PSYCH.6266
  8. Elman, L.B., McCluskey, L. (2021).  Diagnosis of amyotrophic lateral sclerosis and other forms of motor neuron disease. UpToDate. Retrieved August 20, 2021, from  https://www.uptodate.com/contents/diagnosis-of-amyotrophic-lateral-sclerosis-and-other-forms-of-motor-neuron-disease

USMLE™ is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). MCAT is a registered trademark of the Association of American Medical Colleges (AAMC). NCLEX®, NCLEX-RN®, and NCLEX-PN® are registered trademarks of the National Council of State Boards of Nursing, Inc (NCSBN®). None of the trademark holders are endorsed by nor affiliated with Lecturio.

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

User Reviews

0.0

()

¡Hola!

Esta página está disponible en Español.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.

Details