What is the clinical presentation of conus medullaris syndrome?

Clinical Presentation of Conus Medullaris Syndrome

Conus medullaris syndrome (CMS) typically presents with a combination of lower limb pain, sensorimotor disturbances, and bowel/bladder dysfunction, with bladder dysfunction being the most prominent and consistent feature.

Anatomical Considerations

• The conus medullaris represents the terminal end of the spinal cord, typically located at the L1-L2 disc space by 2 months after birth; a conus medullaris ending below the middle third of the L2 vertebra is considered tethered 1
• CMS results from damage to the conus medullaris portion of the spinal cord, which contains the sacral segments responsible for bowel, bladder, and sexual function 1, 2

Key Clinical Features

Urinary Symptoms

• Bladder dysfunction is the hallmark feature of CMS, typically presenting as urinary retention or dysuria 3
• Patients may experience difficulty initiating urination, incomplete emptying, or complete urinary retention 2, 3
• Bladder paralysis is common in acute presentations 4

Bowel Dysfunction

• Bowel dysfunction typically manifests as constipation or fecal incontinence 2
• Loss of anal tone and decreased perianal sensation are common findings 5

Sensory Abnormalities

• Saddle anesthesia (loss of sensation in the perineal region, buttocks, and inner thighs) is a characteristic finding 1, 2
• Perineal hypoalgesia may be present even when lower extremity sensation is preserved 3
• Sensory deficits typically follow a dermatomal pattern corresponding to sacral segments (S3-S5) 5

Motor Symptoms

• Lower extremity weakness is variable and may be absent in some cases 3
• When present, weakness typically affects distal muscle groups more than proximal ones 2
• Patients may present with a mixed upper and lower motor neuron syndrome, distinguishing it from pure cauda equina syndrome (which is exclusively lower motor neuron) 2

Pain Characteristics

• Back and/or leg pain is common and may be:
  • Dull and aching
  • Sharp or lancinating
  • Electrical or dysesthetic in character 1
• Pain may be aggravated by flexion and extension of the spine or by walking/running 1
• Buttock and posterior thigh pain is often a prominent initial symptom in cases of conus medullaris infarction 5

Reflexes

• Deep tendon reflexes in the lower extremities are typically diminished or absent 2
• Ankle reflexes are particularly affected 2

Distinguishing Features from Cauda Equina Syndrome

• CMS often presents with a mixed upper motor neuron (hyperreflexia, increased tone) and lower motor neuron (areflexia, flaccidity) syndrome, while cauda equina syndrome presents with pure lower motor neuron findings 2
• Bladder dysfunction tends to be more prominent and occurs earlier in CMS compared to cauda equina syndrome 3, 5
• Pain is often less severe in CMS compared to cauda equina syndrome 2

Progression and Long-term Complications

• Untreated CMS can lead to progressive musculoskeletal deformities and/or scoliosis 1
• Muscle atrophy may become apparent over time 1
• The skin of the leg and foot may become thin, shiny, and hairless due to autonomic changes with long-standing tethering 1
• Sexual dysfunction is common and may persist even after treatment 2

Special Considerations

• In traumatic cases, CMS may be associated with thoracolumbar junction injuries, particularly L1 burst fractures 6
• Non-traumatic causes include tethered cord syndrome, spinal lipomas, and other fatty infiltrations of the filum terminale 1
• Ischemic CMS (infarction of the conus medullaris) can present acutely with prominent buttock and posterior thigh pain 5
• Isolated CMS without lower extremity involvement is extremely rare but can occur with direct compression of the conus medullaris 3

Early recognition of these symptoms is crucial for timely intervention, as delayed treatment may result in permanent neurological deficits affecting bowel, bladder, and sexual function 2, 6.