What is conus medullaris syndrome?

What is Conus Medullaris Syndrome

Conus medullaris syndrome (CMS) is a complex neurological disorder resulting from injury or compression of the conus medullaris—the terminal end of the spinal cord that typically ends at the L1-L2 disc space—characterized by a distinctive combination of upper motor neuron signs (spasticity, hyperreflexia) and lower motor neuron signs (flaccid paralysis, areflexia), with prominent early bladder and bowel dysfunction. 1, 2, 3

Anatomical Definition

• The conus medullaris is the tapered terminal portion of the spinal cord, normally ending at the L1-L2 disc space by 2 months after birth 1
• A conus that ends below the middle third of the L2 vertebra is considered abnormally tethered 1
• The conus transitions into the cauda equina (nerve roots), which explains why CMS presents with mixed upper and lower motor neuron findings 2, 3

Clinical Presentation

Bladder and Bowel Dysfunction (Hallmark Features)

• Bladder dysfunction is the most prominent feature and occurs earlier in CMS compared to cauda equina syndrome, presenting as urinary retention, urgency, or incontinence 1
• Bowel dysfunction manifests as early-onset fecal incontinence 1
• Bladder paralysis is common in acute presentations 1

Motor and Sensory Findings

• Mixed upper and lower motor neuron signs distinguish CMS from pure cauda equina syndrome 2, 3
• Lower extremity weakness with variable patterns of spasticity (UMN) or flaccidity (LMN) depending on the exact level of injury 2, 4
• Perineal or saddle anesthesia is characteristic 5, 3
• Hyperreflexia may be present below the level of the lesion 1

Pain Patterns

• Back and/or leg pain (unilateral or bilateral) is common 1, 5
• Pain may be dull and aching, sharp, lancinating, electrical, or dysesthetic in character 1
• Pain can be aggravated by spinal flexion/extension or by walking or running 1

Rare Presentations

• Pure CMS without lower extremity involvement is extremely rare but has been documented, particularly with direct conus compression 4

Etiology

Traumatic Causes

• Burst fractures at the thoracolumbar junction (T12-L2) are common traumatic causes 2, 5
• Traumatic spinal cord injuries have an annual incidence of 10-85 cases per million persons worldwide 1

Non-Traumatic Causes

• Congenital malformations: tethered cord syndrome, myelomeningocele, spinal lipomas, fatty infiltrations of the filum terminale 1
• Disc herniation: including rare intradural disc herniation 4
• Vascular: ischemic and hemorrhagic infarcts 1
• Demyelinating diseases: multiple sclerosis, MOG-associated encephalomyelitis (conus lesions are a recognized feature) 6, 1
• Neoplastic: metastatic tumors 1

Diagnostic Evaluation

Imaging

• MRI is the preferred and essential imaging modality, providing superior visualization of soft tissue, bone marrow, and spinal canal 1, 3
• Urgent MRI is recommended in all patients with suspected CMS given the low sensitivity of clinical examination alone 3
• CT can supplement evaluation of bony structures 7
• Post-myelographic CT can identify intradural pathology 4
• SPECT and bone scans may show persistent injury during follow-up rehabilitation 2

Neurological Examination

• Focus on assessment of perineal sensation, evaluation of anal tone, and testing of lower limb reflexes 1
• Look for mixed UMN signs (hyperreflexia, spasticity) and LMN signs (flaccidity, areflexia) 2, 3
• Document bladder and bowel function carefully 3

Management Principles

Surgical Timing

• Surgical decompression is recommended within 48 hours, preferably within less than 24 hours 3
• Early diagnosis and treatment are crucial to avoid long-term neurological deficits 7
• Posterior decompression with removal of compressive lesions is the standard approach 2, 4

Conservative Management

• Conservative treatment may be considered for non-compressive etiologies or mild cases 7
• There is no established data supporting the use of steroids in acute CMS 3

Prognosis and Complications

Recovery Patterns

• UMN injuries (higher conus lesions) demonstrate prolonged recovery periods with persistent spasticity 2
• Immediate postoperative improvement in bladder function can occur with successful decompression 4
• Long-standing untreated tethering results in progressive musculoskeletal deformities, scoliosis, and muscle atrophy 1

Long-term Sequelae

• Orthopedic deformities of the feet and spine may develop 1
• Autonomic changes can cause thin, shiny, hairless skin on the leg and foot 1
• Hydrocephalus is a rare complication with certain pathologies 1

Key Distinguishing Features from Cauda Equina Syndrome

• Earlier and more prominent bladder/bowel dysfunction in CMS 1
• Presence of UMN signs (hyperreflexia, spasticity) in CMS versus pure LMN signs in cauda equina syndrome 2, 3
• CMS involves actual spinal cord injury, while cauda equina syndrome involves only nerve root compression 3