CNS nontumor
Toxic and metabolic disorders
Subacute combined degeneration

Author: Kymberly A. Gyure, M.D. (see Authors page)

Revised: 18 August 2017, last major update September 2015

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Subacute combined degeneration CNS
Cite this page: Gyure, K.A. Subacute combined degeneration. PathologyOutlines.com website. http://pathologyoutlines.com/topic/cnssubacutecombined.html. Accessed September 24th, 2017.
Definition / general
  • Acquired myelopathy caused by vitamin B12 (cobalamin) deficiency
Sites
  • Posterior and lateral columns of spinal cord
Pathophysiology
  • Adenosylcobalamin and methylcobalamin are metabolites of cobalamin; they are coenzymes in reactions which (a) convert methylmalonyl CoA to succinyl CoA and (b) transfer methyl groups to homocysteine to form methionine, respectively
  • Accumulation of methylmalonyl CoA causes a decrease in normal myelin synthesis and incorporation of abnormal fatty acids into neuronal lipids
Etiology
  • Cobalamin deficiency: vegetarian diet
  • Impaired absorption of cobalamin intrinsic factor (IF) complex: pernicious anemia / atrophic gastritis, partial gastrectomy, fish tapeworm infection, Imerslund-Gräsbeck syndrome (genetic defect of cobalamin IF complex receptor), Crohn disease
  • Subacute combined degeneration can be triggered by exposure to nitrous oxide in B12 deficient patients
Clinical features
  • Progressive sensory abnormalities, ascending paresthesias, weakness, ataxia, loss of sphincter control and gait impairment
Diagnosis
  • Schilling test: radiolabeled cyanocobalamin is administered orally and its excretion is measured in the urine
  • Increased serum methylmalonic acid and homocysteine concentrations
  • Decreased serum cobalamin concentration
  • Macrocytic / megaloblastic anemia
Radiology description
  • Symmetric, increased T2 signal confined to posterior and lateral columns of the cervical and thoracic spinal cord
Radiology images

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Cervical spinal cord MRI

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Brain MRI

Prognostic factors
  • Less severe disease at time of diagnosis, including absence of sensory dermatomal deficits, Romberg sign and Babinski sign, is associated with a higher rate of resolution following cobalamin replacement therapy
Case reports
Treatment
  • Intramuscular cobalamin injections
Gross description
  • Shrunken spinal cord with discoloration of the posterior and lateral columns
Microscopic (histologic) description
  • Bilaterally symmetric myelin loss and degeneration in the posterior and lateral columns of the spinal cord
  • Dense gliosis in longstanding cases
Microscopic (histologic) images

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Contributed by Dr. Kymberly Gyure

Peripheral smear images

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Bone marrow aspiration

Differential diagnosis
  • Tabes dorsalis: does not affect lateral columns of spinal cord
  • Vacuolar myelopathy of acquired immunodeficiency syndrome: thought to be related to abnormal vitamin B12 metabolism but serum B12 levels are typically normal