CBL: Cauda Equina & Conus Medullaris Syndromes

Progressive gait difficulty, saddle anesthesia, and bowel/bladder involvement.

Topic: Neuro-spine Level: Resident

Learning Objectives

  • Recognize hallmark features of cauda equina syndrome (CES), including saddle anesthesia and LMN signs.
  • Appreciate that outcomes depend on timely diagnosis and treatment.
  • Differentiate CES from conus medullaris syndrome (CMS) by reflexes, pattern of weakness, and bladder findings.

Case History

Patient: 66-year-old man with progressive difficulty walking over 3 weeks.

PMH: Non-Hodgkin lymphoma (1 year ago; cyclophosphamide, vincristine, prednisone, rituximab).

Symptoms: Gradual thigh numbness → leg weakness; sharp thigh pains; progressed from cane to walker; PT ineffective. Bowel/bladder control impaired; reduced perineal sensation. No constipation or frank urinary retention. Minimal back pain; no trauma.

Social: Former smoker (45 pack-years, quit 18 months), retired grocery clerk; no alcohol.

ROS: No fever, weight loss, or systemic symptoms.

Examination

Vitals: T 97.5°F, P 82, BP 141/83.

General: Overweight, ambulates slowly with walker; cognition/cranial nerves/upper extremities normal.

Motor (LE): Hip flex 4/5 bilat; hip ext 5/5; knee ext/flex 4/5; ankle dorsiflex 3/5; plantarflex 3/5 (R) / 4/5 (L).

Reflexes: Biceps/triceps 2+; quads/gastrocs absent. Plantars flexor.

Sensation: Normal in arms, trunk, lower legs; impaired inner thighs, perineum, perianal region (saddle anesthesia).

Coordination: Cannot perform heel–knee–shin; finger–nose normal.

Gait: Very slow, bent knees, requires arm support.

Localization & Neuroanatomy

  • Weakness with hyporeflexia, saddle anesthesia, and bowel/bladder involvement localize to sacral roots of the cauda equina.
  • Pattern mimics peripheral neuropathy, but the bilateral, sharply localized distribution favors sacral root pathology.
CES vs CMS
Feature Cauda Equina Syndrome Conus Medullaris Syndrome
Reflexes Hyporeflexia (LMN) Hyperreflexia (UMN)
Bowel/Bladder Incontinence, leakage Retention, constipation
Motor Asymmetric weakness More symmetric weakness
Sensory Saddle anesthesia Saddle anesthesia (often abrupt onset)

Common Causes — CES

  • Spinal stenosis; disk herniation
  • Infiltrative/metastatic malignancy
  • Infection (epidural abscess)
  • Hematoma; traumatic injury
  • Inflammatory conditions

Common Causes — CMS

  • Spinal cord infarct
  • Intramedullary tumors (e.g., ependymoma, glioblastoma)
  • Multiple sclerosis

Work-up

  • MRI lumbar spine (first-line).
  • If MRI negative/inconclusive: CSF analysis and EMG/NCS as appropriate.

Treatment

Malignancy-related CES

  • Often metastatic; prognosis guarded.
  • Multimodal therapy: radiation, chemotherapy; surgery in select cases.
  • Early neurosurgery & radiation oncology consults are essential.

Degenerative/Stenotic CES

  • Surgical decompression is often beneficial.

Outcomes depend on severity and duration of deficits prior to treatment — delayed diagnosis is associated with worse recovery.

Review Questions

Question 1

CES would be most suspicious if:

  • a. Numbness in legs/feet with diminished reflexes
  • b. Leg numbness + bladder incontinence
  • c. Saddle numbness + diminished reflexes
  • d. Difficulty walking + leg numbness
  • e. All of the above

Question 2

CES is difficult to treat because:

  • a. Cause seldom found
  • b. Underlying conditions (malignancy, infection, stenosis) often resist treatment
  • c. Often misdiagnosed
  • d. Treatment unknown
  • e. Surgical treatments not optimized

Question 3

Key differences between CES & CMS include:

  • a. Numbness of legs
  • b. Weakness of legs
  • c. Diminished vs increased reflexes
  • d. Loss of bladder/bowel sensation
  • e. Incontinence vs retention
  • f. Both C and E

Teaching Points

  • CES is a clinical emergency—localize with exam and image urgently.
  • Look for the triad: saddle anesthesia, LMN reflex pattern, and bladder/bowel involvement.
  • Distinguish CES (roots) from CMS (cord) by reflexes and bladder pattern.

References

  1. Emergency evaluation of back pain with neurologic deficits: MRI first for suspected CES.
  2. Neuro-oncology and spine surgery guidelines for malignancy-related root compression.