Conus Medullaris Syndrome (CMS)
Conus medullaris syndrome (CMS) is a neurological disorder resulting from injury to the conus medullaris, the terminal portion of the spinal cord, characterized by varying degrees of lower limb weakness, sensory disturbances, and bowel/bladder dysfunction.
Anatomy and Pathophysiology
- The conus medullaris is located at the end of the spinal cord and continues to the cauda equina, typically ending at the L1-L2 disc space by 2 months after birth 1
- Radiographically, a conus medullaris that ends below the middle third of the L2 vertebra is considered tethered 1
- CMS results from damage to the conus medullaris, which can be caused by various factors including trauma, disc herniation, tumors, or inflammatory conditions 2, 3
- Unlike cauda equina syndrome (CES), which is a pure lower motor neuron injury, CMS often presents with a mixed upper motor neuron and lower motor neuron syndrome 4
Clinical Manifestations
- Symptoms of CMS are age-dependent and may include pain, sensorimotor disturbances of the lower limbs, and difficulties with bladder and/or bowel control 1
- Back and/or leg pain is common and may be dull and aching, sharp, lancinating, electrical, or dysesthetic in character 1
- Pain may be aggravated by flexion and extension of the spine or by walking or running 1
- Sensory abnormalities generally start distally in the leg and become more proximal over time; occasionally a "suspended" sensory loss may be present 1
- Bladder and bowel dysfunction may manifest as urinary and fecal urgency and/or incontinence, urinary tract infections, dribbling urinary stream, incomplete emptying, or inability to void 1
- Perineal or saddle anesthesia is a characteristic finding 2, 3
- In some cases, CMS may present without lower extremity involvement, which is extremely rare 2
Diagnostic Evaluation
- MRI is the preferred imaging method for diagnosing CMS as it provides better visualization of soft tissue, bone marrow, and spinal canal 5
- CT can be used as a supplementary imaging method, especially when evaluating bony structures 5
- Diagnosis should be based on a combination of clinical examination and imaging diagnostics 5
- Post-myelographic CT may be useful in cases where direct compression of the conus medullaris is suspected 2
Differential Diagnosis
- Cauda equina syndrome (CES) - a pure lower motor neuron injury affecting the nerve roots below the conus medullaris 3, 4
- Tethered cord syndrome - results from physical stretching of the spinal cord leading to impaired blood flow and metabolic failure 1
- Inflammatory conditions such as MOG-associated disease can present with conus medullaris syndrome 6
- High-riding conus medullaris syndrome - presents with more exclusive upper motor neuron signs 7
Management
- Early diagnosis and treatment are crucial to avoid long-term neurological deficits 5
- Surgical decompression is often necessary for traumatic or compressive lesions of the conus medullaris 2, 3
- Posterior decompression and stabilization offers at least equivalent neurological outcomes as nonoperative or anterior approaches for traumatic injuries 4
- For inflammatory causes like MOG-associated disease, corticosteroids may be effective 6
- Early transfer to specialized spinal cord injury centers is crucial but often delayed, potentially depriving patients of timely interventions 8
Prognosis
- The prognosis for CMS varies depending on the cause, timing of intervention, and extent of injury 3, 4
- Patients with CMS often retain ambulatory motor function but may have persistent bowel, bladder, and sexual dysfunctions 4
- Surgical treatment for CMS without lower extremity involvement caused by intradural disc herniation has shown effectiveness 2
- High-riding injuries to the conus medullaris may have a more prolonged recovery period due to upper motor neuron involvement 7
Complications and Long-term Outcomes
- Long-standing untreated tethering can result in progressive musculoskeletal deformities and/or scoliosis 1
- Muscle atrophy may become apparent, with thinning of calf muscles and/or "saber shins" 1
- Orthopedic deformities of the feet and spine, such as progressive scoliosis and exaggerated lumbosacral lordosis, may develop 1
- With long-standing tethering, the skin of the leg and foot may become thin, shiny, and hairless due to autonomic changes 1