What is the epidemiology of conus medullaris syndrome?

Epidemiology of Conus Medullaris Syndrome

Conus medullaris syndrome (CMS) is a rare neurological disorder with limited epidemiological data, but it occurs most commonly due to traumatic injuries at the thoracolumbar junction, with other causes including disc herniation, tumors, and congenital malformations. 1, 2

Anatomical Considerations

• The conus medullaris represents the terminal portion of the spinal cord, typically ending at the L1-L2 disc space by 2 months after birth; a conus that ends below the middle third of the L2 vertebra is considered tethered 1
• CMS involves injury to the terminal portion of the spinal cord, resulting in a mixed upper and lower motor neuron syndrome, distinguishing it from cauda equina syndrome which presents as a pure lower motor neuron injury 3

Traumatic CMS Epidemiology

• Traumatic spinal cord injuries have an annual incidence ranging from 10 to 85 cases per million persons worldwide 4
• The thoracolumbar junction is particularly vulnerable to trauma, making it a common location for injuries that can result in CMS 3, 2
• Epidemiological trends in spinal cord injuries are evolving, with an increasing proportion of cervical incomplete SCIs in older persons from low-energy or fall-related mechanisms 4
• The mean age of patients suffering acute spinal cord injury increased from 40.5 years to 50.5 years between 1993 and 2012 in the United States 4

Etiology of CMS

• Traumatic causes include burst fractures at the thoracolumbar junction 5, 6
• Non-traumatic causes include:
  • Intradural disc herniation (rare cause) 7
  • Congenital malformations such as tethered cord syndrome 1, 4
  • Spinal lipomas and other fatty infiltrations of the filum terminale 4
  • Meningoceles and atretic meningoceles (rare) 4

Clinical Presentation

• CMS presents with variable symptoms depending on the level and extent of injury 1, 2
• Common symptoms include:
  • Back and/or leg pain (may be dull, aching, sharp, or dysesthetic) 1
  • Sensorimotor disturbances of the lower limbs 1, 3
  • Bladder and bowel dysfunction 1, 2
  • Saddle anesthesia 3, 2
• In rare cases, CMS may present without lower extremity involvement, as documented in case reports 7
• Long-standing untreated cases can develop progressive musculoskeletal deformities, scoliosis, and skin changes (thin, shiny, hairless skin of the leg and foot) due to autonomic dysfunction 1

Diagnostic Considerations

• MRI is the preferred imaging method for diagnosing CMS 1
• The location of the conus medullaris relative to the level of greatest canal compromise is important for accurate diagnosis, though this is not always specifically evaluated in clinical practice 3

Prognostic Factors

• Neurological outcomes in CMS are influenced by:
  • Timing of intervention (early decompression may improve outcomes) 5
  • Level and severity of injury 3
  • Presence of mixed upper and lower motor neuron signs 6
• High-riding injuries to the conus medullaris tend to present with more prominent upper motor neuron signs and may have prolonged recovery periods 6

Treatment Outcomes

• Overall, patients with CMS typically retain ambulatory motor function but may have persistent bowel, bladder, and sexual dysfunctions 3
• Posterior decompression and stabilization offers at least equivalent neurological outcomes compared to nonoperative or anterior approaches 3
• Surgical treatment for CMS caused by intradural disc herniation has been reported to be effective in case studies 7

While CMS is a relatively rare condition with limited epidemiological data, its impact on quality of life can be significant due to the potential for persistent neurological deficits, particularly affecting bowel and bladder function.