CONTENTS

• Spinal cord basics
  • Anatomy
  • Recognizing spinal cord injury
  • Lesion localization
  • Bowel and bladder symptoms
• Spinal cord radiology
  • Patterns of axial involvement
  • Patterns of longitudinal involvement
• Acute & subacute myelopathy
  • Potential causes
  • Investigation
    • Blood tests
    • CSF evaluation
    • Imaging
• Specific myelopathies
  • Spinal cord infarction
  • Spinal dural arteriovenous fistula (dAVF)
  • Spinal epidural hematoma
  • Cauda equina syndrome
  • Nitrous oxide
• Podcast
• Questions & discussion
• Pitfalls

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anatomy

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general anatomy

• Spinal nerves and corresponding sensory dermatomes are shown above. Note that the spinal cord level doesn't line up precisely with the corresponding vertebrae, especially caudal to the thoracic spine.

defining the level of a spinal cord lesion

• Sensory spinal cord level:
  • Light touch is perceived by both the spinothalamic tract and the dorsal columns. Therefore, a sensory level to light touch may be absent unless both of these are involved (e.g., a complete injury that involves all spinal cord tracts).
  • Evaluating for a sensory level using a pin to detect pain sensation is more sensitive to detect a spinal level originating from a lesion in the spinothalamic tract.
• Motor spinal cord level:
  • Patients with partial cord involvement may fail to display a sensory level. Motor weakness may be used to evaluate the level of a spinal lesion that involves the corticospinal tract. Muscles corresponding to various spinal levels are listed below:(27907952)
• C5
  • Elbow flexion (biceps).
  • Shoulder flexion, extension, abduction (deltoids), adduction, internal/external rotation.
• C6
  • Wrist flexion.
  • Elbow pronation.
• C7
  • Elbow extension (triceps).
  • Finger: Flexion at proximal joint, extension
  • Thumb: Flexion, extension, and abduction in plane of thumb
• C8
  • Finger flexion at MCP joint.
  • Thumb: Opposition, adduction and abduction perpendicular to palm
• T1
  • Abduction of the 2nd and 5th fingers.
• L2
  • Hip flexion.
• L3
  • Knee extension.
  • Hip external rotation.
• L4
  • Foot dorsiflexion.
  • Hip extension, abduction, internal rotation
  • Knee flexion
  • Toe: Metacarpal and interphalangeal extension
• L5
  • Great toe dorsiflexion (movement towards the shin).
• S1
  • Foot plantar flexion.

basic functional anatomy of the spinal cord

• Three major tracts run through the spinal cord, as shown below. Different involvement of these three tracts explains the major patterns of spinal cord injury (e.g., hemicord injury causing Brown-Sequard syndrome; more on this below).
• Nerves to the cervical cord are located closest to the middle of the cord, whereas nerves to the sacrum are located farthest towards the edges of the spinal cord. Thus, a central spinal cord lesion may cause neurologic deficits in a descending order.

more detailed spinal cord anatomy

• The figure below shows more anatomic detail. Most of the additional pathways shown here cannot be tested clinically, so they cannot assist in lesion localization.
• The ventral (anterior) horns of the grey matter contain lower motor neurons. Thus, diseases affecting the anterior horn of the spinal cord cause flaccid paralysis.
• Autonomic nerves run within the grey matter, near the center of the cord.

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recognizing spinal cord injury

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The first step towards diagnosis and therapy is recognizing that the patient has some sort of spinal cord pathology. This may be harder than it sounds, because spinal cord disease is uncommon and not generally high on our list of considerations.

red flags for spinal cord disease

• Concerning contexts:
  • Trauma.
  • Known malignancy (especially metastatic).
  • Gram-positive bacteremia (especially endocarditis); unexplained fever.
• Back or neck pain.
• Loss of bowel/bladder/sexual function (especially: acute urinary retention).
• Common localizing features:
  • Bilateral weakness and/or numbness (if present, a sensory level is strongly suggestive).
  • Without signs of brain dysfunction (e.g., no cranial nerve abnormalities, aphasia, confusion).
  • With signs of upper motor neuron dysfunction (e.g., hyperreflexia, clonus, spasticity, Babinski sign).
• Lhermitte's sign (an electric-shock sensation elicited by neck flexion that runs down the spine and sometimes into the limbs) suggests involvement of the posterior columns of the cervical spinal cord.(34062569) This is most closely associated with demyelinating lesions, but may also occur with other pathologies.(33522735)

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lesion localization

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some pearls

• 💡 Hyperactive reflexes in the legs with less active arm reflexes suggest thoracic myelopathy (although a cervical lesion is also possible).(Alpert 2019)
• 💡 The sensory and/or motor level may be considerably below the lesion level.(Alpert 2019)

Brown-Sequard (hemicord) syndrome

• Clinical findings:
  • Below the lesion:
    • Ipsilateral weakness (corticospinal tract).
    • Ipsilateral loss of vibration & proprioception (dorsal column).
    • Contralateral loss of pain & temperature (spinothalamic tract).
  • At the level of the lesion, there may be 1-2 dermatomes with ipsilateral weakness, loss of vibration & proprioception, and loss of pain & temperature. This occurs because the spinothalamic tract nerves are damaged before they have a chance to cross the midline (figure above).
• More common causes:
  • Penetrating trauma (1-5% of traumatic spinal cord injuries).
  • Neoplasm, especially an extra-axial lesion which is compressing the spinal cord (e.g., meningioma); radiation myelopathy.
  • Unilateral demyelinating lesion.

anterior cord syndrome

• Clinical findings:
  • The first finding may be that pain & temperature sensation loss below the lesion (spinothalamic tracts).
  • With more severe lesions, motor function is lost below the lesion (due to involvement of the bilateral corticospinal tracts).
    • Lower motor neuron findings for a small segment of the spinal cord, at the level of the lesion (due to destruction of motor nerves in the anterior spinal cord).
    • Upper motor neuron findings below the level of the lesion.
  • Incontinence is common.
  • Vibration & proprioception should be preserved (dorsal columns are spared).
• More common causes: Most often due to infarction of the anterior spinal artery. Other causes may include trauma or multiple sclerosis.

central cord syndrome

• Clinical findings:
  • (#1) First affected structure: Decussation of the anterolateral tracts causes loss of pain & temperature to the bilateral body at the level of the lesion. For lesions in the cervical cord, this may create a cape-like distribution affecting the arms and upper back.
  • (#2) If the lesion expands, spinothalamic +/- corticospinal tracts may be affected.
    • Occurs in a descending distribution (e.g., affecting nerves to the cervical spine first).
    • Pain/temperature may be affected first (spinothalamic tract), with motor losses later on (corticospinal tract).
    • An advanced central cord lesion may spare the sacral dermatomes, creating the inverse pattern compared to cauda equina syndrome (figure above).
  • (#3) Signs of myelopathy (e.g., urinary incontinence).
• Most common causes:
  • Neck hyperextension cervical spinal cord injury (spinal cord contusion).
  • Syrinx (dilation of the central canal of the spinal cord).
  • Any lesion causing obstruction of the central canal (e.g., tumor, demyelination, hemorrhage, trauma).

posterior cord syndrome (dorsal columns)

• Clinical findings: Bilateral impairment of proprioception and vibration.
• Causes: (34062569)
  • Syphilis (tabes dorsalis).
  • Multiple sclerosis.
  • Posterior spinal artery infarct.
  • Copper deficiency.
  • B12 deficiency.
  • Platinum-based chemotherapy.
  • Trauma with hyperextension.
  • Extrinsic spinal cord compression.

subacute combined degeneration (aka, posterolateral syndrome)

• Clinical findings: Bilateral impairment of proprioception and vibration (dorsal columns) as well as upper motor neuron weakness (corticospinal tract).
• Causes: Deficiency of vitamin B12, vitamin E, or copper; zinc toxicity; HIV-associated vacuolar myelopathy; HTLV myeloneuropathy (human T-cellymphotropicic virus); intrathecal methotrexate; compressive myelopathy; spinal dural arteriovenous fistula.(34062569)

other features of spinal cord injury

• Neurogenic shock. 📖
• Hypothermia may occur due to inappropriate vasodilation leading to heat loss.
• Respiratory failure may result from high C-spine involvement.

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bowel and bladder findings in spinal cord lesions

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some basic neuroanatomy

• Sympathetic afferents arise from T11-L1.
• Parasympathetic afferents and coordinating skeletal muscles arise from S2-S4.
• Damage to bilateral pathways is usually required to cause bladder dysfunction.

bladder symptoms due to lesion above S2-S4

• Acute effect:
  • Flaccid (atonic) bladder.
  • Persistent reflex contraction of the urethral sphincter.
  • Urinary retention occurs, causing acute bladder distension. Catheterization is usually necessary to relieve bladder distension (although overflow incontinence may also occur).
• Chronic effect evolves over weeks/months:
  • Hyperreflexic (spastic) bladder.
  • Urinary frequency and urge incontinence occur.
  • Dyssynergy exists between the bladder detrusor and urinary sphincter, which prevents complete emptying of the bladder.

bladder symptoms due to lesion at S2-S4, or spinal nerves

• Flaccid (atonic) bladder.
• Baseline relaxation of the urethral sphincter causes urine to leak out of the bladder (stress incontinence).

bowel symptoms due to spinal cord dysfunction

• Bowel symptoms mirror bladder symptoms (for example, acute injury or injury to S2-S4 may cause flaccid rectal tone with constipation and incontinence).
• Urination normally happens several times daily, whereas defecation occurs less frequently. Thus, bladder dysfunction will tend to manifest before bowel dysfunction.

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patterns of axial involvement

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central

• Neuromyelitis optica spectrum disorders.
• MOG-associated diseases (MOGAD), including ADEM (acute disseminated encephalomyelitis). 📖
• Infectious myelitis (EBV, Lyme, or HCV-associated myelitis).(34798966)
• Arteriovenous fistula.
• Radiation.

peripheral

• Multiple sclerosis.
• If extending to the dorsal root, this suggests Lyme or HSV myelitis.

centripetal

• Sarcoidosis.
• Tuberculosis.
• Infiltrative processes, such as malignancy.

central gray matter

• Infarction.
• Anterior compression.
• Arteriovenous fistula.
• MOG-associated diseases (MOGAD). 📖

dorsal column

• B12 deficiency (including B12 deficiency due to nitrous oxide abuse).
• Copper deficiency (including deficiency due to chronic zinc use or to bariatric surgery).
• Paraneoplastic conditions.
• Chronic infections (syphilis, VZV, JC virus, HIV-induced vacuolar myelopathy).

anterior horns

• Spinal cord infarction.
• Infectious myelitis, usually pathogens that cause acute flaccid myelitis (e.g., enterovirus 71; enterovirus D68; West Nile virus and other flaviviruses; poliovirus; coxackieviruses A9, A16, B2, B4; echoviruses).

nerve root enhancement (radiculitis)

• Viral infections (e.g., CMV, VZV, HSV-2, HIV, West Nile virus).(34798966)
• Fungal or mycobacterial infections (e.g., histoplasmosis, blastomycosis, cryptococcosis, tuberculosis).
• Lyme disease.
• Guillain-Barre syndrome.
• Neurosarcoidosis.
• Leptomeningeal carcinomatosis.

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patterns of longitudinal involvement

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The length of T2-hyperintense lesions can help sort out various inflammatory lesions of the spinal cord:

1-2 vertebral segments:

• Often suggests multiple sclerosis.📖
• MOG-associated disease may cause a combination of short and long lesions.📖

3 or more vertebral segments (longitudinally extensive):

• Neuromyelitis optica spectrum disorders may be the most common cause.📖
• MOG-associated disease may cause a combination of short and long lesions.📖
• GFAP-IgG (glial fibrillary acidic protein IgG) associated myelitis.
• Paraneoplastic.
• Neurosarcoidosis, Lupus, Sjogren's syndrome.
• Infectious myelitis or postinfectious (including HIV, VZV 📖, West Nile Virus, enterovirus, and syphilis).(34030191)
• Nutritional deficiency (B12 or copper).
• Dural AV fistula.
• Radiation myelitis.
• Medication-related (e.g., methotrexate).

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acute & subacute myelopathies

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Acute myelopathy is defined as reaching peak severity within 24 hours, subacute is defined as reaching a peak within 1-21 days, and chronic is defined as reaching a peak after >21 days. Acute myelopathies usually reflect vascular or traumatic events, whereas subacute and chronic myelopathies have a broader differential diagnosis. The division between acute/subacute/chronic is often imprecise (for example, some processes may progress either gradually or acutely). The differential below focuses on acute and subacute processes, as these will be more likely to be encountered in the intensive care unit.

causes of compressive myelopathy

• Trauma. 📖
• Degenerative spine disease.
• Infection (epidural abscess, tuberculosis involving the vertebral bodies).
• Neoplastic (metastases, meningioma).
• Hemorrhage (e.g., epidural hematoma).
• Fatty infiltration of the epidural space (lipomatosis).(LaHue 2021)

iatrogenic

• Chemotherapy (especially intrathecal chemotherapy).
• Radiation myelopathy (usually chronic, but acute deterioration is possible).
• Immune checkpoint inhibitors 📖
• TNF-alpha inhibitors (MRI may show single/multiple demyelinating lesions).
• Status post spinal/aortic surgery.

inflammatory

• Primary:
  • Multiple sclerosis myelitis.📖
  • Neuromyelitis optica spectrum disorders.📖
  • MOG-associated diseases (MOGAD), including ADEM (acute disseminated encephalomyelitis).📖
  • Idiopathic transverse myelitis.📖
  • Paraneoplastic (GFAP antibody, CRMP-5-IgG antibody).
• Systemic rheumatologic disorder:
  • Lupus.
  • Sjogren's disease.
  • Sarcoidosis.

infectious

• Bacterial:
  • Epidural abscess.📖
  • Lyme disease.
  • Tuberculosis.
  • Neurosyphilis 📖 (may cause myelitis or spinal cord infarction due to meningovasculitis).
• Viral:
  • West Nile virus.
  • Enteroviruses (including coxsackievirus, echovirus, poliovirus).
  • Herpesviruses (HSV, CMV, EBV, VZV, HHV6).
    • HSV 1 or HSV 2 (most commonly Elsberg syndrome – lumbosacral involvement in association with genital herpes).
    • VZV myelitis may be associated with viral reactivation in the context of herpes zoster.
  • HIV.
• Toxoplasmosis (MRI may show an enhancing, expansile mass).

neoplastic

• Primary spinal cord neoplasm (usually chronic, but acute onset can occur with high-grade tumor or hemorrhage).
• Metastatic spinal cord involvement.📖

toxic/metabolic

• B12 deficiency.
  • Nitrous oxide 📖 abuse may cause acute presentations.
• Copper deficiency (may result from zinc ingestion e.g. denture cream, bariatric surgery).
• Vitamin E deficiency.
• Cocaine or heroin.

vascular

• Spinal cord infarction. 📖
• Epidural hematoma. 📖
• Dural arteriovenous fistula. 📖
• (Disorders more likely to be chronic: arteriovenous malformation, cavernous malformation.)

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blood tests

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laboratory studies to consider include:

• General labs:
  • Complete blood count, liver and kidney function tests.
  • Erythrocyte sedimentation rate, C-reactive protein.
• Rheumatologic:
  • Antinuclear and extractable nuclear antigens.
  • Antineutrophil cytoplasmic antibodies.
  • Serum testing for MOG-IgG and for IgG against aquaporin-4 (more sensitive than CSF evaluations for these antibodies).(34619778)
  • Serum panels for autoimmune/paraneoplastic serologies may be considered.
• Infectious:
  • HIV screening.
  • Blood cultures, if epidural abscess is possible.
  • Syphilis testing. 📖
  • Lyme testing. 📖
• Metabolic:
  • Vitamin B12.
  • Vitamin E.
  • Copper.
  • Methylmalonic acid level, if nitrous oxide poisoning is possible.

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CSF evaluation

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CSF tests to consider

• Basic chemistries.
• Oligoclonal bands and IgG level (to evaluate IgG index).
• Infectious evaluation:
  • PCR for HSV-1/2, VZV, and enterovirus.
  • Additional tests based on clinical context.
• Cytology.
• Autoimmune/paraneoplastic antibody panel.

cell count

• Most autoimmune/inflammatory myelitis will cause some elevation of CSF white blood cell count, usually with a lymphocytic predominance. A normal CSF cell count might suggest an alternative disorder (e.g., a vascular abnormality).(33522737) However, mild elevation of white blood cell count (e.g., 10-25 cells/mm3) may be seen in noninflammatory disorders (e.g., spinal cord infarction) due to secondary inflammation.(33522737; 33522736)
• Multiple sclerosis usually causes a mild pleocytosis, so >50 white blood cells in the CSF may suggest an alternative diagnosis.(34619778, 34798965) >5% neutrophils also suggests that multiple sclerosis is unlikely.(34030191)
• MOG-associated disorders, neuromyelitis optica spectrum disorders, and GFAP antibody-associated myelitis may be associated with CSF white blood cell counts up to ~1,000 cells/mm3.(33522737)

oligoclonal banding

• Detection of two or more oligoclonal bands in the CSF that aren't found in the serum is considered indicative of intrathecal immunoglobulin synthesis.(34030191) This has a broad differential diagnosis, including various inflammatory or infectious processes involving the central nervous system.
• Oligoclonal banding is typically seen in MS (with a sensitivity of ~90%), but may be seen less often in tumefactive MS (~50%).(34798965) It is uncommon in neuromyelitis optica spectrum disorder and MOG-IgG-related myelitis (15-20%).
• Various other causes of oligoclonal bands are:

IgG index

• This may be used to evaluate for inflammatory myelitis.
• IgG index is less sensitive than oligoclonal banding for intrathecal IgG synthesis detection (e.g., it is elevated in only 75% of patients with multiple sclerosis).
• False positive results are common due to blood-CSF barrier dysfunction.(34030191)

CSF autoimmune serologies

• Autoimmune/paraneoplastic panels should be considered. In particular, CSF is the most sensitive assay to test for GFAP-IgG.
• MOG antibody may be considered (although serum testing for MOG is generally more sensitive).

additional discussion of other CSF abnormalities may be found here: 📖

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imaging

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• Spinal cord MRI is the imaging modality of choice.  If there is concern for vascular abnormalities, an MRI/MRA may be helpful.
• Brain MRI may be helpful in revealing more systemic processes such as ADEM (acute disseminated encephalomyelitis), multiple sclerosis, neuromyelitis optica spectrum disease, MOGAD, or neurosarcoidosis.

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spinal cord infarction

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clinical findings

• Usually involves the anterior spinal artery infarction, causing bilateral weakness with sparing of dorsal columns. This usually involves the thoracic cord (as opposed to inflammatory myelitis, which more often involves the cervical spinal cord).(34024334)
• Onset is generally hyperacute, but symptoms may subsequently increase over 12-24 hours due to edema surrounding the ischemic core.(34619778)
  • 💡 Hyperacute onset (reaching peak severity within <~4 hours) suggests spinal cord ischemia.(34024334)
• Symptoms include most commonly:
  • Sensory level with loss of pain and temperature sensation (often at the thoracic level).
  • Motor deficit (often flaccid paraplegia).
  • Acute radicular back pain may occur, which can radiate in a belt-like distribution. Pain is common in spontaneous spinal cord infarction (~60%), but not in periprocedural spinal cord infarction (15%).(33522736)

causes

• Embolic:
  • Cardioembolic.
  • Aortic atheroembolism.
  • Fibrocartilaginous embolism (may be caused by a Valsalva maneuver, heavy lifting, trauma, or intense physical activity).
  • Decompression sickness following diving.
• Dissection (aortic, subclavian, or vertebral).
• Vasculitis (e.g., lupus, ANCA vasculitis, giant cell arteritis, VZV vasculopathy, syphilis).
• Hypotension (cardiac arrest, profound shock/hypotension).
• Iatrogenic:(33896530)
  • Aortic surgery (open or endovascular).
  • Angiography (e.g., renal artery embolization).
  • Cardiac catheterization.
  • ECMO.
• Surfer's myelopathy and other situations involving back hyperextension.
• Hypercoagulability (e.g., malignancy, antiphospholipid syndrome, sickle cell disease).
• Idiopathic (about one-third of patients; this may relate in some cases to atherosclerosis).(30709470)

imaging

• MRI may be normal within the first 24 hours in up to 80% of cases.(33896530)
• The first change may be restricted diffusion weighted imaging (DWI). This is useful if seen, but may perform poorly due to artefacts (when compared to the use of DWI for ischemic infarctions in the brain). Unfortunately, diffusion-weighted imaging may also be abnormal in acute inflammatory demyelinating processes.(34024334)
• Over time, a T2-hyperintense lesion will develop.
  • On sagittal imaging, this may appear as an anterior pencil-like stripe.(34024334)
  • On axial imaging, the grey matter is often diffusely involved, producing an “H-shaped” pattern. Alternatively, watershed territory infarction may produce an axial “snake eyes” pattern due to involvement of the anterior horn cells (which are most vulnerable to ischemia).
• Initially there is no expansion or contrast enhancement of the lesion. However, delayed imaging may show expansion due to ongoing edema, as well as contrast enhancement.(30709470)
• CT angiography may allow for vascular imaging of the aorta and the spinal artery of Adamkiewicz.(33896530)

investigation of the etiology

• If the cause of infarction is unclear, then further evaluation may be warranted (similar to the evaluation of a patient with cryptogenic stroke). The following tests may be considered:
• Lumbar puncture for usual tests, along with IgG index, oligoclonal bands, VZV PCR and IgG, and VRDL (for syphilis).
• Vasculitis evaluation (e.g., ESR, CRP, ANCA, ANA).
• EKG and transthoracic echocardiogram with bubble study.
• Hypercoagulability evaluation (e.g., evaluation for antiphospholipid antibody syndrome).

management

• Early blood pressure augmentation may be considered (e.g., targeting a MAP >80-90 mm, or targeting an increase by 10-20 mm – ideally while observing for evidence of clinical improvement).(34798966; 33896530; 33522736)
• Spinal fluid drainage to improve spinal cord perfusion may be considered, but data on this is mixed.(34798966) Evidence may be more robust for spinal drainage to manage infarction following endovascular or open thoracoabdominal aortic surgery.(33896530)
• Supportive care should address consequences of spinal cord dysfunction. Depending on the level of injury, these may include respiratory muscle weakness, urinary retention, and gastric/intestinal hypomotility (e.g., gastroparesis, constipation). (33896530)

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spinal dural arteriovenous fistula

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basics

• An aberrant connection between a dural vein and artery leads to excessive pressure in the vein. This causes impaired perfusion and tissue edema (aka, congestive myelopathy).
• Usually affects the lower half of the thoracic spinal cord, from T4-L3.(34619778; 30709470)

epidemiology

• Most common type of spinal vascular malformation, accounting for ~75% of all spinal vascular lesions.(33896530)
• Most frequent in men in their 50's or older.(34024334)

clinical features

• Initial symptoms may include gait disturbance (96% of patients), back pain, and asymmetric/ascending sensory disturbance (including radicular symptoms and patchy sensory loss).
• Bowel and bladder dysfunction may occur later. (34024334; 35419159) If untreated, additional spinal levels may become affected in an ascending fashion (Foix-Alajouanine syndrome). (30709470)
• Can present acutely in about a fifth of cases. Episodic clinical worsening may occur after exertion, straining, lumbar puncture, or steroid administration.(35419159) However, in most cases myelopathy is a slow and insidious process.(33896530)
  • ⚠️ If dural AV fistula is suspected, this is a relative contraindication to lumbar puncture.(35419159)

imaging

• MRI findings:
  • Usually causes a longitudinally extensive, thoracic lesion involving the central spinal cord that is hyperintense on T2 sequences. Any longitudinally extensive T2-hyperintense lesion in the thoracic spine should lead to strong consideration for dural AV fistula.(34619778) Unfortunately, nonspecific T2 hyperintensity often leads to a misdiagnosis of transverse myelitis.(33896530)
  • Venous dilation may be seen in the form of prominent paraspinal T2 flow voids along the posterior surface of the spinal cord in ~50-80% of cases. If seen, these are nearly pathognomonic (but they may occur with other types of arteriovenous malformation or certain tumors).(33522736)
  • Gadolinium enhancement is common, which may cause misdiagnosis as an inflammatory or neoplastic disorder. Focal nonenhancing areas may occur within an area of diffuse enhancement (“missing piece sign”).(34619778)
• Diagnosis often requires invasive angiography or MR angiography.

treatment

• The AV fistula may be ligated either surgically or via endovascular occlusion. Underlying spinal tissue often remains viable, so patients typically experience neurological improvement after ligation of the fistula.

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spinal epidural hematoma

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causes (28435919)

• Trauma.
• Iatrogenic (e.g., surgery, epidural catheterization, or lumbar puncture).
• Arteriovenous malformation.
• Pregnancy.
• Coagulopathy.
• Spontaneous:
  • Rare, usually among patients above ~40 years old.(31902412)

symptoms

• (1) Sudden-onset pain (typically located in back/neck).
• (2) Spinal cord dysfunction (e.g., motor deficits, urinary retention).

imaging

• MRI is superior to CT scan.
• Vascular imaging may be considered to exclude an underlying vascular malformation.

management

• (1) Coagulopathy should be emergently reversed.
• (2) Surgery:
  • As with any etiology of spinal cord compression, emergent surgery may avoid chronic neurologic deficits. Early intervention may allow for recovery of neurologic deficits.
  • If patients are asymptomatic or have minimal/improving neurological deficits, conservative management with close observation might be an option.(33522736) However, outcomes are typically poor without surgical intervention.(28435919)

going further

• Case report: 82-year-old woman with acute-onset left-sided weakness (Lobo et al. PMID 31902412) 📄

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cauda equina syndrome

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basics

• The cauda equina is composed of nerve roots L2-L5 and S1-S5, which exit the spinal cord below the end of the spinal cord (figure below). Functions of these nerves include the following:(33522743)
  • L2-S3: Leg movement and sensation.
  • S2-S4: Genitalia sensation, bladder function, external anal sphincter.
  • S4-S5: Sensation overlying the coccyx.
• Cauda equina syndrome lacks a precise definition. It is generally used to refer to pathologies which damage several of these nerve roots.

more common causes (33522743)

• Structural spinal disease:
  • Lumbar disc herniation (most common cause, responsible for ~45% of cases).
  • Spinal stenosis, ankylosing spondylitis.
  • Trauma.
• Vascular:
  • Spinal epidural hematoma.
  • Dural arteriovenous fistula.
  • Aortic disease causing ischemia (e.g., dissection, thrombosed aneurysm).
  • Thrombosis/occlusion of the inferior vena cava causing enlargement of the epidural venous plexus.
• Neoplasm:
  • Primary or metastatic tumor causing extrinsic compression.
  • Leptomeningeal carcinomatosis.
  • Radiation-induced.
  • Intrathecal methotrexate or cytarabine.
• Infection:
  • Spinal epidural abscess.📖
  • HSV-2 (Elsberg syndrome), HSV-1, CMV, VZV, HIV.
  • Lyme disease, syphilis.
  • Neurocysticercosis, cryptococcosis, tuberculosis.
• Other rare causes:
  • Sarcoidosis.
  • Extramedullary hematopoiesis.

possible symptoms

• Back pain and leg pain, especially bilateral sciatica radiating down both legs.(31471075) This is the most common presenting symptom.(31471075)
• Urinary dysfunction may be the most reliably reported autonomic symptom, allowing it to help grade the severity of injury:(33522743; 31471075)
  • Complete cauda equina dysfunction causes painless urinary retention and overflow incontinence.
  • Incomplete cauda equina dysfunction may cause altered urinary sensation, poor urinary stream, or the need to strain during urination.
• Sensory loss may be unilateral or bilateral, most often involving the posterior thighs, buttocks, and perineum.(33522743)
• Leg weakness.
• Other signs of autonomic dysfunction:
  • Sexual dysfunction (e.g., dyspareunia, impotence, priapism, urination during intercourse).(33522743)
  • Bowel retention or incontinence.

constellation of symptoms

• Individual patients may have variable symptoms, due to involvement of different nerves.
• Disease course may vary in acuity, depending on the cause (e.g., gradually enlarging neoplasm vs. acute disc herniation).

examination findings

• Reduced/absent reflexes and weakness may be seen in the legs. However, cauda equina syndrome involving only the lower nerve roots (e.g., S2-S5) may spare leg strength. The following should be carefully evaluated:
  • Hip flexion (L2).
  • Knee extension (L3).
  • Foot dorsiflexion (L4) and plantar flexion (S1).
  • Great toe dorsiflexion (L5).
  • Patellar and Achilles tendon reflexes.
• Loss of sensation in the legs or perineum.
• Post-void residual volume in the bladder >200 ml was reported to be 94% sensitive and 72% specific in one prospective study.(31479434)
• 🛑 Rectal tone is not useful, since assessments are subjective and inaccurate.(33522743, 31471075) However, a careful evaluation of skin sensation to pinprick in the perirectal area should be performed (including sensation on both sides of the anus). Unilateral or bilateral perianal numbness has a higher sensitivity and specificity than rectal tone.(31479434)

imaging

• Lumbar spine MRI with contrast is the test of choice. If this is negative, imaging of the cervical and thoracic cord should be considered (to look for a central cord syndrome at a higher level that may be masquerading as cauda equina syndrome).
• CT scan with contrast may detect bony abnormalities of the spinal canal (e.g., spinal stenosis), but is less sensitive for soft tissue disorders. CT myelogram has higher performance, but it is more invasive and may be more difficult to obtain.

lumbar puncture

• Lumbar puncture is initially contraindicated, since this could exacerbate a spinal epidural abscess or epidural hematoma.
• After performing an MRI, if the etiology remains unclear then lumbar puncture may help evaluate for leptomeningeal carcinomatosis or infection.

differential diagnoses may include:

• Spinal cord lesion in the conus medullaris (more on this below; overall significance is similar to cauda equina syndrome).
• Spinal cord lesion in the cervical or thoracic cord (especially a central cord lesion).
• Guillain-Barre syndrome (GBS).📖

management

• Any compressive lesion causing cauda equina syndrome is a neurosurgical emergency. Alleviating pressure earlier may improve neurological outcomes. Similar to spinal cord compression, disability at the time of surgery is the primary predictor of neurologic outcome.
• Noncompressive etiologies may require specific therapy, depending on the cause.

conus medullaris syndrome

• Conus medullaris syndrome refers to pathology at the very end of the spinal cord (usually at the T12-L1 level). This is difficult to distinguish from cauda equina syndrome, but the difference often isn't important – the clinical significance of both syndromes is similar.(Alpert 2019)
• Some differences compared to cauda equina syndrome:
  • Weakness may be spastic and symmetric (rather than flaccid).
  • If sensory loss is dissociated (e.g., with loss of pain/temperature, put preservation of touch/vibration/proprioception), this suggests a lesion in the conus medullaris of the spinal cord.(27907952)

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nitrous oxide

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basics

• Nitrous oxide is a colorless, odorless gas (“laughing gas”) which is used medically for its sedative and anesthetic properties. Unfortunately, it has also become a drug of abuse.
• Nitrous oxide causes oxidation of the cobalt ion within vitamin B12, rendering B12 dysfunctional. This can cause patients to present with various neurologic findings, reflective of deficient B12 function.(34713284)

epidemiology

• Abuse:
  • Nitrous oxide is inexpensive and easily purchased as a propellent for whipped cream dispensers (often in small metallic canisters termed “nangs,” “chargers,” “bulbs,” or “whippits”). Nitrous oxide is also known as “hippy crack” or “sweet air.”(35945749)
  • Nitrous oxide appears to be increasingly abused. A survey in 2019 found it to be among the top ten most frequently used recreational drugs globally.(33590530)
  • Clinical disease typically results from frequent, heavy use for months. The abuse of nitrous oxide is considerably more common than its neurologic sequelae, as most patients who are exposed don't manifest with clinical disease.
• Nitrous oxide is used medically as a sedative (especially for dentistry). The medical utilization of nitrous oxide may rarely cause toxicity, predominantly among patients with low B12 stores prior to exposure.

clinical presentation

• Clinical features may include the following, with varying presentations among different patients:
• (1) Subacute combined degeneration of the spinal cord:
  • Prominent dysfunction of the posterior columns (leading to loss of vibration perception or proprioception).
  • Dysfunction of the corticospinal tract (causing upper motor neuron weakness).
• (2) Peripheral neuropathy:
  • May cause lower motor neuron involvement.
  • 💡 Peripheral neuropathy may produce hypoactive reflexes, despite the presence of other clinical signs of upper motor neuron disease (e.g., Babinski's sign).
  • May cause sensory loss in a stocking/glove distribution, sometimes with painful dysesthesias.
• (3) Neuropsychiatric features:
  • Delirium or psychosis (“megaloblastic madness”).
  • Personality changes, depression, or mania.
• (4) Other neurologic features which may be seen:
  • Lhermitte's sign.
  • Optic neuropathy causing visual disturbance.
  • Autonomic dysfunction may occur rarely (e.g., urinary and fecal incontinence, impotence).
• (5) Additional features of B12 deficiency may be present in patients with chronic nitrous oxide abuse:
  • Atrophic glossitis (smooth, beefy-red tongue).
  • Angular cheilitis (sores at the corners of the mouth).
  • Hypercoagulability may result from elevated levels of homocysteine, which may promote either venous or arterial thrombosis.

investigation

• Anemia with elevated MCV (mean corpuscular volume) may occasionally be present. Hypersegmented neutrophils may also suggest the diagnosis, if they happen to be found on a blood smear.
• Serum vitamin B12 levels can be normal or low (the vitamin is rendered dysfunctional, but absolute levels of the vitamin are not depleted). If B12 levels do happen to be low, consider the possibility of nitrous oxide exposure combined with underlying B12 deficiency (e.g., due to pernicious anemia or various medications).(34713284)
• Elevated methylmalonic acid (MMA) level reflects functional B12 deficiency. Methylmalonic acid is fairly specific for B12 deficiency, but it may also be elevated in renal insufficiency, hypovolemia, or methylmalonic aciduria. This is arguably the best single test to detect nitrous oxide toxicity.
• Homocysteine levels are also elevated, but this is less specific for B12 deficiency (as it may also be seen in folate deficiency, renal failure, B6 deficiency, hereditary homocysteinemia, or hypothyroidism).(34713284)
• MRI may show T2 hyperintensity in the dorsal columns with ~75% sensitivity (typically in the cervical spine).(35150382) White matter changes may occur in the brain MRI.(35695047)

management

• Education and discontinuation of nitrous oxide.
• Aggressive, parenteral hydroxocobalamin (B12) supplementation.
  • Theoretically, saturating the body with functional B12 could displace dysfunctional B12 and thereby more rapidly improve cellular metabolism. This implies that B12 administration should be done more aggressively than with doses typically utilized to replete patients who have B12 deficiency.(35695047)
  • B12 is a water-soluble vitamin, so overdose is largely impossible. The optimal dose for this scenario is unknown.
  • Initial treatment might be 1,000 mcg of intramuscular B12 daily for a week. After a week this could be spaced out and perhaps supplemented with oral high-dose B12 (e.g., 2,000 mcg daily).
  • For the most critical patients, it might not be unreasonable to administer an induction dose of 70 mg/kg B12 intravenously (or ~5,000 mcg). This regimen has been established to be safe, based on its utilization among patients with possible cyanide exposure. 🌊
• Folic acid 5 mg daily may be started following initial B12 doses (to avoid exacerbation of the functional B12 deficiency).(35150382)
• Many patients may use several substances, so support should be provided for other substance use disorders as well (e.g., suboxone for opioid use disorder).

prognosis & follow-up

• Substantial improvement should be seen with therapy.
• Lack of improvement suggests an alternative diagnosis, or ongoing abuse of nitrous oxide.

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questions & discussion

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To keep this page small and fast, questions & discussion about this post can be found on another page here.

• Failure to consider the possibility of an acute myelopathy.
• Failure to evaluate promptly for compression of the spinal cord (as this may require emergent decompression). (LaHue 2021)
• Use of rectal tone in an attempt to exclude cauda equina syndrome.

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• = Link to IBCC section about a drug.
• = Link to IBCC section covering that topic.
• = Link to FOAMed site with related information.
• 📄 = Link to open-access journal article.
• = Link to supplemental media.