Subacute Combined Degeneration of the Spinal Cord

Question 1

Full syndrome of B12 deficiency

Answer 1

• Diffuse effect on the spinal cord, primarily the posterior and lateral columns (starting with the fasciculus gracilis)
• Usually presents as paresthesias in the hand and feet with loss of vibration and proprioception. May present with megaloblastic anemia.
• Late in the disease course:
  
  • Optic atrophy
  • Sensory ataxia
  • Cognitive changes
  • Lateral corticospinal tract dysfunction (manifesting as distal weakness in the legs with UMN signs)
  • Other exam findings:
    
    • Reddening of the tongue
    • Graying of the hair at an early age

Question 2

All the things required for proper absorption of B12

Answer 2

• Diet containing sources of B12 (meats, typically)
• R-protein/Transcobalamin I (produced by salviary glands, protects B12 until it can bind with intrinsic factor)
• Parietal cells (to produce intrinsic factor)
• Intrinsic factor (to bind B12)
• Stomach acid (to provide an environment for intrinsic factor binding)
• Distal ileum (to absorb intrinsic factor-B12 complex)
• Transcobalamin II (to delivery B12 to tissues)

Question 3

Most common cause of B12 deficiency

Answer 3

Malabsorption due to pernicious anemia

Question 4

Etiologies of B12 deficiency

Answer 4

• Pernicious anemia
• Any form of malabsorption
  
  • IBD
  • Celiac’s
  • Bariatric surgery
  • Parasitosis
  • Medications
  • Alcohol
  • Genetic disorders
• Vegan diet
• Malnourishment

Question 5

Syndrome of subacute combined degeneration

Answer 5

Sensory loss and spastic paraparesis associated with pathologic lesions in the dorsal columns and lateral corticospinal tracts

Question 6

__ is always on the ddx for B12 deficiency

Answer 6

Cu deficiency is always on the ddx for B12 deficiency

Best way to differntiate is by looking at blood. Copper causes a microcytic anemia, B12 causes a macrocytic anemia.

Question 7

DDx for progressive spastic paraplegia

Answer 7

• B12 deficiency
• Copper deficiency
• HIV-1 associated vacuolar myelopathy
• Lyme disease
• Neurosyphilis
• Multiple sclerosis
• Toxic neuropathy

Question 8

Clinical definitions of B12 deficiency

Answer 8

• Serum B12 level < 150 pmol/L on two separate occasions
• Serum B12 level < 150 pmol/L AND total serum homocysteine > 13 μmol/L (in the absence of renal failure, folate deficiency, and B6 deficiency)

Question 9

In cases where you suspect B12 deficiency, but the hematologic findings are not a slam-dunk, ___ is imporant to support the diagnosis

Answer 9

In cases where you suspect B12 deficiency, but the hematologic findings are not a slam-dunk, checking for elevated methylmalonate and homocysteine is imporant to support the diagnosis

Question 10

Will folate deficiency ever mimic B12 deficiency?

Answer 10

ONLY for hematologic features

NOT for neuropathic features

Question 11

Imaging findings consistent with B12 deficiency

Answer 11

• MRI hyperintensity on T2 weighted imaging in the dorsal columns and sometimes the lateral pyramidal tracts
• Modest expansion in size of the cervical and thoracic spinal cord (due to edema)

Question 12

Treatment of B12 deficiency

Answer 12

• For intramuscular:
  
  • 1 mg/day for 1 week
  • 1 mg/wk for 1 month
  • Then 1 mg/month until testing shows overcorrection, OR for life in the case of pernicious anemia
• Oral replenishment with very high doses is also an option

Question 13

Secondary causes of copper deficiency

Answer 13

• Acquired:
  
  • Intestinal disease (Celiac’s, Crohn’s, etc)
  • Gastric bypass surgery
  • Excessive zinc supplementation
• Genetic:
  
  • Menke’s disease
  • Wilson’s disease overtreatment (fairly common in Wilson patients)

Question 14

Nerve conduction studies show both __ and __ features in B12 deficiency

Answer 14

Nerve conduction studies show both demyelinating and denervation features in B12 deficiency