Fact-sheet: Subacute combined degeneration of the cord - Combined sclerosis of the spinal cord
Updated on 03/25/2022 at 12:07 PM
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Definition
Combined degeneration of the spinal cord is a rare cause of myelopathy.
It most often corresponds to involvement of the posterior columns (tract carrying deep sensation, proprioception).
Involvement may also, less frequently, affect the lateral corticospinal tract (motor function) and the spinothalamic tract (crude touch, pain, temperature).
This condition is most often due to vitamin B12 deficiency, whose most common etiology in Western countries is pernicious anemia (Biermer disease, an autoimmune condition). The active form of vitamin B12 is necessary for myelin production and DNA synthesis. Vitamin deficiency results in weakening of nerve fibers and axonal lesions. Spinal cord involvement begins at the low cervical and high thoracic levels, in scattered patches, then the lesions spread laterally, longitudinally, and transversely. Early diagnosis is necessary for reversibility of the clinical neurological involvement and of the radiological findings. Otherwise, spastic paraplegia may occur, along with sphincter disorders.
Other etiology with increasing incidence: Nitrous oxide intoxication
Clinical features
Proprioceptive ataxia and signs of pyramidal irritation with progressive, subacute onset, over a few weeks.
Patients may thus present with lower limb weakness, lower limb paresthesias, gait difficulties, and balance disorders.
Lhermitte's sign.
Laboratory findings
Vitamin B12 deficiency:
- Biological vitamin B12 assay: markedly decreased level.
- Elevated homocysteine and methylmalonic acid levels.
- Macrocytic anemia (or normocytic in cases of superimposed iron deficiency), aregenerative.
- Sometimes, detection of anti-IF antibodies (intrinsic factor) in the setting of pernicious anemia (Biermer disease).
MRI
Spinal MRI:
T2 hyperintensity within the spinal cord affecting the posterior columns, involving several myelomeres (demyelinating lesions).
Sometimes, T1 hypointensity of the spinal cord lesions.
Early cord enlargement, before later progressing to atrophy (after several months of evolution).
Inconsistent contrast enhancement of the lesions after gadolinium injection (related to increased permeability of the blood-spinal cord barrier).
Management
Vitamin supplementation (intramuscular vitamin B12 injections).
In pernicious anemia (Biermer disease): upper gastrointestinal endoscopy (atrophic gastritis).
Differential diagnosis
Other causes of myelopathy with posterior column involvement:
- Autoimmune, infectious, vascular, neoplastic, metabolic, degenerative conditions...
- Friedreich's ataxia (spinocerebellar degeneration)
- Vitamin E deficiency