Subacute Combined Degeneration of the Spinal Cord

Aka: Subacute Combined Degeneration of the Spinal Cord, Subacute Combined Degeneration, Spinal Cord SCD

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II. Pathophysiology

  1. Demyelination of the spinal cord Dorsal Columns (Posterior Columns)
    1. May also affect the Spinothalamic Tracts (lateral columns)
    2. Vitamin B12 is important to myelin synthesis and repair
    3. Longterm Vitamin B12 Deficiency results in myelin degradation
  2. Causes a progressive ascending Polyneuropathy (especially sensory)

III. Causes

  1. Vitamin B12 Deficiency (most common)
  2. Longterm Methotrexate use (via effects on Folate metabolism)
  3. Longterm Nitrous Oxide Abuse
    1. Nitrous Oxide inhalation irreversibly inactivates Vitamin B12 by cobalt atom oxidation
    2. Longterm Nitrous Oxide Abuse results in Vitamin B12 Deficiency
    3. Long segmental changes involving the Posterior Columns

IV. Symptoms: Classic Presentation

  1. Ataxia
    1. Imbalance and falls
    2. Fine motor Incoordination (dropping objects)
  2. Spastic paraparesis
    1. Muscle stiffness, spasms or weakness
    2. Lower extremity weakness or Incoordination (ultimately involving arms) may also occur
  3. Sensory changes
    1. Distal extremity Paresthesias (starting with legs, ultimately involving arms)
    2. Patient may describe as "Numbness"

V. Signs

  1. Distinguishing Features of Posterior Column disease
    1. Proprioception and vibratory Sensation loss
    2. Pain and TemperatureSensation loss
  2. Other findings not specific for SCD but may be associated in more severe or progressive cases
    1. Lower extremity Deep Tendon Reflexes diminished or lost (or hyperreflexia in some cases)
    2. Positive Babinski Reflex

VI. Differential Diagnosis

  1. See Symmetric Peripheral Neuropathy
  2. Transverse Myelitis
  3. Multiple Sclerosis
  4. Neurosyphilis
  5. Cerebellar Conditions
  6. Epidural spinal abscess (or other compressive spinal cord lesions)
  7. Other nutritional deficiencies (Copper deficiency, Vitamin E deficiency)

VII. Labs

  1. Macrocytic Anemia
  2. Decreased Serum Vitamin B12

VIII. Imaging

  1. MRI Brain
    1. Typically unaffected in Subacute Combined Degeneration (SCD)
    2. Obtain MRI Brain to exclude other pathology (e.g. cerebellar conditions)
  2. MRI Spinal Cord (esp. cervical and Thoracic Spine)
    1. Negative MRI does not exclude SCD
    2. Obtain with and without gadolinium contrast to exclude other conditions on differential
      1. Non-contrast scans are sufficient for the SCD diagnosis
    3. T2 weighted images (FLAIR images may also show changes)
      1. Hyperintense (bright white appearance of the Dorsal Columns)
      2. Inverted V Sign on axial images
        1. Specific for SCD, but only 31-72% sensitive

IX. Management

  1. Vitamin B12 Replacement
    1. Administer Vitamin B12 initially (oral or IM) even in inconclusive cases (e.g. negative MRI)
    2. Initial: Vitamin B12 1000 mcg IM daily for up to 2-3 weeks
    3. Later: Vitamin B12 1000 mcg orally daily

X. References

  1. (2016) EM:Rap 16(12): 1
  2. Broder (2026) Crit Dec Emerg Med 40(2): 23-5
  3. Lin (2011) Acta Neurol Taiwan 20(2): 129-37 +PMID: 21739392 [PubMed]
  4. Pema (1998) Am J Neuroradiol 19:894-6 [PubMed]

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